dnsmasq(8)
NAME
dnsmasq - A lightweight DHCP and caching DNS server.
SYNOPSIS
dnsmasq [OPTION]...
DESCRIPTION
dnsmasq is a lightweight DNS, TFTP, PXE, router advertisement and DHCP server. It is intended to provide coupled DNS and DHCP service to a LAN. Dnsmasq accepts DNS queries and either answers them from a small, local, cache or forwards them to a real, recursive, DNS server. It loads the contents of /etc/hosts so that local hostnames which do not appear in the global DNS can be resolved and also answers DNS queries for DHCP configured hosts. It can also act as the authoritative DNS server for one or more domains, allowing local names to appear in the global DNS. It can be configured to do DNSSEC validation. The dnsmasq DHCP server supports static address assignments and multiple networks. It automatically sends a sensible default set of DHCP options, and can be configured to send any desired set of DHCP options, including vendor-encapsulated options. It includes a secure, read-only, TFTP server to allow net/PXE boot of DHCP hosts and also supports BOOTP. The PXE support is full featured, and includes a proxy mode which supplies PXE information to clients whilst DHCP address allocation is done by another server. The dnsmasq DHCPv6 server provides the same set of features as the DHCPv4 server, and in addition, it includes router advertisements and a neat feature which allows nameing for clients which use DHCPv4 and stateless autoconfiguration only for IPv6 configuration. There is support for doing address allocation (both DHCPv6 and RA) from subnets which are dynamically delegated via DHCPv6 prefix delegation. Dnsmasq is coded with small embedded systems in mind. It aims for the smallest possible memory footprint compatible with the supported functions, and allows uneeded functions to be omitted from the compiled binary.
OPTIONS
Note that in general missing parameters are allowed and switch off
functions, for instance "--pid-file" disables writing a PID file. On
BSD, unless the GNU getopt library is linked, the long form of the
options does not work on the command line; it is still recognised in
the configuration file.
--test Read and syntax check configuration file(s). Exit with code 0 if
all is OK, or a non-zero code otherwise. Do not start up
dnsmasq.
-w, --help
Display all command-line options. --help dhcp will display
known DHCPv4 configuration options, and --help dhcp6 will
display DHCPv6 options.
-h, --no-hosts
Don't read the hostnames in /etc/hosts.
-H, --addn-hosts=<file>
Additional hosts file. Read the specified file as well as
/etc/hosts. If -h is given, read only the specified file. This
option may be repeated for more than one additional hosts file.
If a directory is given, then read all the files contained in
that directory.
--hostsdir=<path>
Read all the hosts files contained in the directory. New or
changed files are read automatically. See --dhcp-hostsdir for
details.
-E, --expand-hosts
Add the domain to simple names (without a period) in /etc/hosts
in the same way as for DHCP-derived names. Note that this does
not apply to domain names in cnames, PTR records, TXT records
etc.
-T, --local-ttl=<time>
When replying with information from /etc/hosts or configuration
or the DHCP leases file dnsmasq by default sets the time-to-live
field to zero, meaning that the requester should not itself
cache the information. This is the correct thing to do in almost
all situations. This option allows a time-to-live (in seconds)
to be given for these replies. This will reduce the load on the
server at the expense of clients using stale data under some
circumstances.
--dhcp-ttl=<time>
As for --local-ttl, but affects only replies with information
from DHCP leases. If both are given, --dhcp-ttl applies for DHCP
information, and --local-ttl for others. Setting this to zero
eliminates the effect of --local-ttl for DHCP.
--neg-ttl=<time>
Negative replies from upstream servers normally contain time-to-
live information in SOA records which dnsmasq uses for caching.
If the replies from upstream servers omit this information,
dnsmasq does not cache the reply. This option gives a default
value for time-to-live (in seconds) which dnsmasq uses to cache
negative replies even in the absence of an SOA record.
--max-ttl=<time>
Set a maximum TTL value that will be handed out to clients. The
specified maximum TTL will be given to clients instead of the
true TTL value if it is lower. The true TTL value is however
kept in the cache to avoid flooding the upstream DNS servers.
--max-cache-ttl=<time>
Set a maximum TTL value for entries in the cache.
--min-cache-ttl=<time>
Extend short TTL values to the time given when caching them.
Note that artificially extending TTL values is in general a bad
idea, do not do it unless you have a good reason, and understand
what you are doing. Dnsmasq limits the value of this option to
one hour, unless recompiled.
--auth-ttl=<time>
Set the TTL value returned in answers from the authoritative
server.
-k, --keep-in-foreground
Do not go into the background at startup but otherwise run as
normal. This is intended for use when dnsmasq is run under
daemontools or launchd.
-d, --no-daemon
Debug mode: don't fork to the background, don't write a pid
file, don't change user id, generate a complete cache dump on
receipt on SIGUSR1, log to stderr as well as syslog, don't fork
new processes to handle TCP queries. Note that this option is
for use in debugging only, to stop dnsmasq daemonising in
production, use -k.
-q, --log-queries
Log the results of DNS queries handled by dnsmasq. Enable a full
cache dump on receipt of SIGUSR1. If the argument "extra" is
supplied, ie --log-queries=extra then the log has extra
information at the start of each line. This consists of a
serial number which ties together the log lines associated with
an individual query, and the IP address of the requestor.
-8, --log-facility=<facility>
Set the facility to which dnsmasq will send syslog entries, this
defaults to DAEMON, and to LOCAL0 when debug mode is in
operation. If the facility given contains at least one '/'
character, it is taken to be a filename, and dnsmasq logs to the
given file, instead of syslog. If the facility is '-' then
dnsmasq logs to stderr. (Errors whilst reading configuration
will still go to syslog, but all output from a successful
startup, and all output whilst running, will go exclusively to
the file.) When logging to a file, dnsmasq will close and reopen
the file when it receives SIGUSR2. This allows the log file to
be rotated without stopping dnsmasq.
--log-async[=<lines>]
Enable asynchronous logging and optionally set the limit on the
number of lines which will be queued by dnsmasq when writing to
the syslog is slow. Dnsmasq can log asynchronously: this allows
it to continue functioning without being blocked by syslog, and
allows syslog to use dnsmasq for DNS queries without risking
deadlock. If the queue of log-lines becomes full, dnsmasq will
log the overflow, and the number of messages lost. The default
queue length is 5, a sane value would be 5-25, and a maximum
limit of 100 is imposed.
-x, --pid-file=<path>
Specify an alternate path for dnsmasq to record its process-id
in. Normally /var/run/dnsmasq.pid.
-u, --user=<username>
Specify the userid to which dnsmasq will change after startup.
Dnsmasq must normally be started as root, but it will drop root
privileges after startup by changing id to another user.
Normally this user is "nobody" but that can be over-ridden with
this switch.
-g, --group=<groupname>
Specify the group which dnsmasq will run as. The defaults to
"dip", if available, to facilitate access to
/etc/ppp/resolv.conf which is not normally world readable.
-v, --version
Print the version number.
-p, --port=<port>
Listen on <port> instead of the standard DNS port (53). Setting
this to zero completely disables DNS function, leaving only DHCP
and/or TFTP.
-P, --edns-packet-max=<size>
Specify the largest EDNS.0 UDP packet which is supported by the
DNS forwarder. Defaults to 4096, which is the
RFC5625-recommended size.
-Q, --query-port=<query_port>
Send outbound DNS queries from, and listen for their replies on,
the specific UDP port <query_port> instead of using random
ports. NOTE that using this option will make dnsmasq less secure
against DNS spoofing attacks but it may be faster and use less
resources. Setting this option to zero makes dnsmasq use a
single port allocated to it by the OS: this was the default
behaviour in versions prior to 2.43.
--min-port=<port>
Do not use ports less than that given as source for outbound DNS
queries. Dnsmasq picks random ports as source for outbound
queries: when this option is given, the ports used will always
to larger than that specified. Useful for systems behind
firewalls.
--max-port=<port>
Use ports lower than that given as source for outbound DNS
queries. Dnsmasq picks random ports as source for outbound
queries: when this option is given, the ports used will always
be lower than that specified. Useful for systems behind
firewalls.
-i, --interface=<interface name>
Listen only on the specified interface(s). Dnsmasq automatically
adds the loopback (local) interface to the list of interfaces to
use when the --interface option is used. If no --interface or
--listen-address options are given dnsmasq listens on all
available interfaces except any given in --except-interface
options. IP alias interfaces (eg "eth1:0") cannot be used with
--interface or --except-interface options, use --listen-address
instead. A simple wildcard, consisting of a trailing '*', can be
used in --interface and --except-interface options.
-I, --except-interface=<interface name>
Do not listen on the specified interface. Note that the order of
--listen-address --interface and --except-interface options does
not matter and that --except-interface options always override
the others.
--auth-server=<domain>,<interface>|<ip-address>
Enable DNS authoritative mode for queries arriving at an
interface or address. Note that the interface or address need
not be mentioned in --interface or --listen-address
configuration, indeed --auth-server will overide these and
provide a different DNS service on the specified interface. The
<domain> is the "glue record". It should resolve in the global
DNS to a A and/or AAAA record which points to the address
dnsmasq is listening on. When an interface is specified, it may
be qualified with "/4" or "/6" to specify only the IPv4 or IPv6
addresses associated with the interface.
--local-service
Accept DNS queries only from hosts whose address is on a local
subnet, ie a subnet for which an interface exists on the server.
This option only has effect is there are no --interface
--except-interface, --listen-address or --auth-server options.
It is intended to be set as a default on installation, to allow
unconfigured installations to be useful but also safe from being
used for DNS amplification attacks.
-2, --no-dhcp-interface=<interface name>
Do not provide DHCP or TFTP on the specified interface, but do
provide DNS service.
-a, --listen-address=<ipaddr>
Listen on the given IP address(es). Both --interface and
--listen-address options may be given, in which case the set of
both interfaces and addresses is used. Note that if no
--interface option is given, but --listen-address is, dnsmasq
will not automatically listen on the loopback interface. To
achieve this, its IP address, 127.0.0.1, must be explicitly
given as a --listen-address option.
-z, --bind-interfaces
On systems which support it, dnsmasq binds the wildcard address,
even when it is listening on only some interfaces. It then
discards requests that it shouldn't reply to. This has the
advantage of working even when interfaces come and go and change
address. This option forces dnsmasq to really bind only the
interfaces it is listening on. About the only time when this is
useful is when running another nameserver (or another instance
of dnsmasq) on the same machine. Setting this option also
enables multiple instances of dnsmasq which provide DHCP service
to run in the same machine.
--bind-dynamic
Enable a network mode which is a hybrid between --bind-
interfaces and the default. Dnsmasq binds the address of
individual interfaces, allowing multiple dnsmasq instances, but
if new interfaces or addresses appear, it automatically listens
on those (subject to any access-control configuration). This
makes dynamically created interfaces work in the same way as the
default. Implementing this option requires non-standard
networking APIs and it is only available under Linux. On other
platforms it falls-back to --bind-interfaces mode.
-y, --localise-queries
Return answers to DNS queries from /etc/hosts which depend on
the interface over which the query was received. If a name in
/etc/hosts has more than one address associated with it, and at
least one of those addresses is on the same subnet as the
interface to which the query was sent, then return only the
address(es) on that subnet. This allows for a server to have
multiple addresses in /etc/hosts corresponding to each of its
interfaces, and hosts will get the correct address based on
which network they are attached to. Currently this facility is
limited to IPv4.
-b, --bogus-priv
Bogus private reverse lookups. All reverse lookups for private
IP ranges (ie 192.168.x.x, etc) which are not found in
/etc/hosts or the DHCP leases file are answered with "no such
domain" rather than being forwarded upstream.
-V, --alias=[<old-ip>]|[<start-ip>-<end-ip>],<new-ip>[,<mask>]
Modify IPv4 addresses returned from upstream nameservers; old-ip
is replaced by new-ip. If the optional mask is given then any
address which matches the masked old-ip will be re-written. So,
for instance --alias=1.2.3.0,6.7.8.0,255.255.255.0 will map
1.2.3.56 to 6.7.8.56 and 1.2.3.67 to 6.7.8.67. This is what
Cisco PIX routers call "DNS doctoring". If the old IP is given
as range, then only addresses in the range, rather than a whole
subnet, are re-written. So
--alias=192.168.0.10-192.168.0.40,10.0.0.0,255.255.255.0 maps
192.168.0.10->192.168.0.40 to 10.0.0.10->10.0.0.40
-B, --bogus-nxdomain=<ipaddr>
Transform replies which contain the IP address given into "No
such domain" replies. This is intended to counteract a devious
move made by Verisign in September 2003 when they started
returning the address of an advertising web page in response to
queries for unregistered names, instead of the correct NXDOMAIN
response. This option tells dnsmasq to fake the correct response
when it sees this behaviour. As at Sept 2003 the IP address
being returned by Verisign is 64.94.110.11
--ignore-address=<ipaddr>
Ignore replies to A-record queries which include the specified
address. No error is generated, dnsmasq simply continues to
listen for another reply. This is useful to defeat blocking
strategies which rely on quickly supplying a forged answer to a
DNS request for certain domain, before the correct answer can
arrive.
-f, --filterwin2k
Later versions of windows make periodic DNS requests which don't
get sensible answers from the public DNS and can cause problems
by triggering dial-on-demand links. This flag turns on an option
to filter such requests. The requests blocked are for records of
types SOA and SRV, and type ANY where the requested name has
underscores, to catch LDAP requests.
-r, --resolv-file=<file>
Read the IP addresses of the upstream nameservers from <file>,
instead of /etc/resolv.conf. For the format of this file see
resolv.conf(5). The only lines relevant to dnsmasq are
nameserver ones. Dnsmasq can be told to poll more than one
resolv.conf file, the first file name specified overrides the
default, subsequent ones add to the list. This is only allowed
when polling; the file with the currently latest modification
time is the one used.
-R, --no-resolv
Don't read /etc/resolv.conf. Get upstream servers only from the
command line or the dnsmasq configuration file.
-1, --enable-dbus[=<service-name>]
Allow dnsmasq configuration to be updated via DBus method calls.
The configuration which can be changed is upstream DNS servers
(and corresponding domains) and cache clear. Requires that
dnsmasq has been built with DBus support. If the service name is
given, dnsmasq provides service at that name, rather than the
default which is uk.org.thekelleys.dnsmasq
-o, --strict-order
By default, dnsmasq will send queries to any of the upstream
servers it knows about and tries to favour servers that are
known to be up. Setting this flag forces dnsmasq to try each
query with each server strictly in the order they appear in
/etc/resolv.conf
--all-servers
By default, when dnsmasq has more than one upstream server
available, it will send queries to just one server. Setting this
flag forces dnsmasq to send all queries to all available
servers. The reply from the server which answers first will be
returned to the original requester.
--dns-loop-detect
Enable code to detect DNS forwarding loops; ie the situation
where a query sent to one of the upstream server eventually
returns as a new query to the dnsmasq instance. The process
works by generating TXT queries of the form <hex>.test and
sending them to each upstream server. The hex is a UID which
encodes the instance of dnsmasq sending the query and the
upstream server to which it was sent. If the query returns to
the server which sent it, then the upstream server through which
it was sent is disabled and this event is logged. Each time the
set of upstream servers changes, the test is re-run on all of
them, including ones which were previously disabled.
--stop-dns-rebind
Reject (and log) addresses from upstream nameservers which are
in the private IP ranges. This blocks an attack where a browser
behind a firewall is used to probe machines on the local
network.
--rebind-localhost-ok
Exempt 127.0.0.0/8 from rebinding checks. This address range is
returned by realtime black hole servers, so blocking it may
disable these services.
--rebind-domain-ok=[<domain>]|[[/<domain>/[<domain>/]
Do not detect and block dns-rebind on queries to these domains.
The argument may be either a single domain, or multiple domains
surrounded by '/', like the --server syntax, eg. --rebind-
domain-ok=/domain1/domain2/domain3/
-n, --no-poll
Don't poll /etc/resolv.conf for changes.
--clear-on-reload
Whenever /etc/resolv.conf is re-read or the upstream servers are
set via DBus, clear the DNS cache. This is useful when new
nameservers may have different data than that held in cache.
-D, --domain-needed
Tells dnsmasq to never forward A or AAAA queries for plain
names, without dots or domain parts, to upstream nameservers. If
the name is not known from /etc/hosts or DHCP then a "not found"
answer is returned.
-S, --local,
--server=[/[<domain>]/[domain/]][<ipaddr>[#<port>][@<source-
ip>|<interface>[#<port>]]
Specify IP address of upstream servers directly. Setting this
flag does not suppress reading of /etc/resolv.conf, use -R to do
that. If one or more optional domains are given, that server is
used only for those domains and they are queried only using the
specified server. This is intended for private nameservers: if
you have a nameserver on your network which deals with names of
the form xxx.internal.thekelleys.org.uk at 192.168.1.1 then
giving the flag -S /internal.thekelleys.org.uk/192.168.1.1 will
send all queries for internal machines to that nameserver,
everything else will go to the servers in /etc/resolv.conf.
DNSSEC validation is turned off for such private nameservers,
UNLESS a --trust-anchor is specified for the domain in question.
An empty domain specification, // has the special meaning of
"unqualified names only" ie names without any dots in them. A
non-standard port may be specified as part of the IP address
using a # character. More than one -S flag is allowed, with
repeated domain or ipaddr parts as required.
More specific domains take precendence over less specific
domains, so: --server=/google.com/1.2.3.4
--server=/www.google.com/2.3.4.5 will send queries for
*.google.com to 1.2.3.4, except *www.google.com, which will go
to 2.3.4.5
The special server address '#' means, "use the standard
servers", so --server=/google.com/1.2.3.4
--server=/www.google.com/# will send queries for *.google.com to
1.2.3.4, except *www.google.com which will be forwarded as
usual.
Also permitted is a -S flag which gives a domain but no IP
address; this tells dnsmasq that a domain is local and it may
answer queries from /etc/hosts or DHCP but should never forward
queries on that domain to any upstream servers. local is a
synonym for server to make configuration files clearer in this
case.
IPv6 addresses may include a %interface scope-id, eg
fe80::202:a412:4512:7bbf%eth0.
The optional string after the @ character tells dnsmasq how to
set the source of the queries to this nameserver. It should be
an ip-address, which should belong to the machine on which
dnsmasq is running otherwise this server line will be logged and
then ignored, or an interface name. If an interface name is
given, then queries to the server will be forced via that
interface; if an ip-address is given then the source address of
the queries will be set to that address. The query-port flag is
ignored for any servers which have a source address specified
but the port may be specified directly as part of the source
address. Forcing queries to an interface is not implemented on
all platforms supported by dnsmasq.
--rev-server=<ip-address>/<prefix-len>,<ipaddr>[#<port>][@<source-
ip>|<interface>[#<port>]]
This is functionally the same as --server, but provides some
syntactic sugar to make specifying address-to-name queries
easier. For example --rev-server=1.2.3.0/24,192.168.0.1 is
exactly equivalent to --server=/3.2.1.in-addr.arpa/192.168.0.1
-A, --address=/<domain>/[domain/][<ipaddr>]
Specify an IP address to return for any host in the given
domains. Queries in the domains are never forwarded and always
replied to with the specified IP address which may be IPv4 or
IPv6. To give both IPv4 and IPv6 addresses for a domain, use
repeated -A flags. Note that /etc/hosts and DHCP leases
override this for individual names. A common use of this is to
redirect the entire doubleclick.net domain to some friendly
local web server to avoid banner ads. The domain specification
works in the same was as for --server, with the additional
facility that /#/ matches any domain. Thus --address=/#/1.2.3.4
will always return 1.2.3.4 for any query not answered from
/etc/hosts or DHCP and not sent to an upstream nameserver by a
more specific --server directive. As for --server, one or more
domains with no address returns a no-such-domain answer, so
--address=/example.com/ is equivalent to --server=/example.com/
and returns NXDOMAIN for example.com and all its subdomains.
--ipset=/<domain>/[domain/]<ipset>[,<ipset>]
Places the resolved IP addresses of queries for the specified
domains in the specified netfilter ip sets. Domains and
subdomains are matched in the same way as --address. These ip
sets must already exist. See ipset(8) for more details.
-m, --mx-host=<mx name>[[,<hostname>],<preference>]
Return an MX record named <mx name> pointing to the given
hostname (if given), or the host specified in the --mx-target
switch or, if that switch is not given, the host on which
dnsmasq is running. The default is useful for directing mail
from systems on a LAN to a central server. The preference value
is optional, and defaults to 1 if not given. More than one MX
record may be given for a host.
-t, --mx-target=<hostname>
Specify the default target for the MX record returned by
dnsmasq. See --mx-host. If --mx-target is given, but not --mx-
host, then dnsmasq returns a MX record containing the MX target
for MX queries on the hostname of the machine on which dnsmasq
is running.
-e, --selfmx
Return an MX record pointing to itself for each local machine.
Local machines are those in /etc/hosts or with DHCP leases.
-L, --localmx
Return an MX record pointing to the host given by mx-target (or
the machine on which dnsmasq is running) for each local machine.
Local machines are those in /etc/hosts or with DHCP leases.
-W, --srv-
host=<_service>.<_prot>.[<domain>],[<target>[,<port>[,<priority>[,<weight>]]]]
Return a SRV DNS record. See RFC2782 for details. If not
supplied, the domain defaults to that given by --domain. The
default for the target domain is empty, and the default for port
is one and the defaults for weight and priority are zero. Be
careful if transposing data from BIND zone files: the port,
weight and priority numbers are in a different order. More than
one SRV record for a given service/domain is allowed, all that
match are returned.
--host-
record=<name>[,<name>....],[<IPv4-address>],[<IPv6-address>][,<TTL>]
Add A, AAAA and PTR records to the DNS. This adds one or more
names to the DNS with associated IPv4 (A) and IPv6 (AAAA)
records. A name may appear in more than one host-record and
therefore be assigned more than one address. Only the first
address creates a PTR record linking the address to the name.
This is the same rule as is used reading hosts-files. host-
record options are considered to be read before host-files, so a
name appearing there inhibits PTR-record creation if it appears
in hosts-file also. Unlike hosts-files, names are not expanded,
even when expand-hosts is in effect. Short and long names may
appear in the same host-record, eg. --host-
record=laptop,laptop.thekelleys.org,192.168.0.1,1234::100
If the time-to-live is given, it overrides the default, which is
zero or the value of --local-ttl. The value is a positive
integer and gives the time-to-live in seconds.
-Y, --txt-record=<name>[[,<text>],<text>]
Return a TXT DNS record. The value of TXT record is a set of
strings, so any number may be included, delimited by commas;
use quotes to put commas into a string. Note that the maximum
length of a single string is 255 characters, longer strings are
split into 255 character chunks.
--ptr-record=<name>[,<target>]
Return a PTR DNS record.
--naptr-
record=<name>,<order>,<preference>,<flags>,<service>,<regexp>[,<replacement>]
Return an NAPTR DNS record, as specified in RFC3403.
--cname=<cname>,<target>[,<TTL>]
Return a CNAME record which indicates that <cname> is really
<target>. There are significant limitations on the target; it
must be a DNS name which is known to dnsmasq from /etc/hosts (or
additional hosts files), from DHCP, from --interface-name or
from another --cname. If the target does not satisfy this
criteria, the whole cname is ignored. The cname must be unique,
but it is permissable to have more than one cname pointing to
the same target.
If the time-to-live is given, it overrides the default, which is
zero or the value of -local-ttl. The value is a positive integer
and gives the time-to-live in seconds.
--dns-rr=<name>,<RR-number>,[<hex data>]
Return an arbitrary DNS Resource Record. The number is the type
of the record (which is always in the C_IN class). The value of
the record is given by the hex data, which may be of the form
01:23:45 or 01 23 45 or 012345 or any mixture of these.
--interface-name=<name>,<interface>[/4|/6]
Return a DNS record associating the name with the primary
address on the given interface. This flag specifies an A or AAAA
record for the given name in the same way as an /etc/hosts line,
except that the address is not constant, but taken from the
given interface. The interface may be followed by "/4" or "/6"
to specify that only IPv4 or IPv6 addresses of the interface
should be used. If the interface is down, not configured or non-
existent, an empty record is returned. The matching PTR record
is also created, mapping the interface address to the name. More
than one name may be associated with an interface address by
repeating the flag; in that case the first instance is used for
the reverse address-to-name mapping.
--synth-domain=<domain>,<address range>[,<prefix>]
Create artificial A/AAAA and PTR records for an address range.
The records use the address, with periods (or colons for IPv6)
replaced with dashes.
An example should make this clearer. --synth-
domain=thekelleys.org.uk,192.168.0.0/24,internal- will result in
a query for internal-192-168-0-56.thekelleys.org.uk returning
192.168.0.56 and a reverse query vice versa. The same applies to
IPv6, but IPv6 addresses may start with '::' but DNS labels may
not start with '-' so in this case if no prefix is configured a
zero is added in front of the label. ::1 becomes 0--1.
The address range can be of the form <ip address>,<ip address>
or <ip address>/<netmask>
--add-mac[=base64|text]
Add the MAC address of the requestor to DNS queries which are
forwarded upstream. This may be used to DNS filtering by the
upstream server. The MAC address can only be added if the
requestor is on the same subnet as the dnsmasq server. Note that
the mechanism used to achieve this (an EDNS0 option) is not yet
standardised, so this should be considered experimental. Also
note that exposing MAC addresses in this way may have security
and privacy implications. The warning about caching given for
--add-subnet applies to --add-mac too. An alternative encoding
of the MAC, as base64, is enabled by adding the "base64"
parameter and a human-readable encoding of hex-and-colons is
enabled by added the "text" parameter.
--add-cpe-id=<string>
Add a arbitrary identifying string to o DNS queries which are
forwarded upstream.
--add-subnet[[=[<IPv4 address>/]<IPv4 prefix length>][,[<IPv6
address>/]<IPv6 prefix length>]]
Add a subnet address to the DNS queries which are forwarded
upstream. If an address is specified in the flag, it will be
used, otherwise, the address of the requestor will be used. The
amount of the address forwarded depends on the prefix length
parameter: 32 (128 for IPv6) forwards the whole address, zero
forwards none of it but still marks the request so that no
upstream nameserver will add client address information either.
The default is zero for both IPv4 and IPv6. Note that upstream
nameservers may be configured to return different results based
on this information, but the dnsmasq cache does not take
account. If a dnsmasq instance is configured such that different
results may be encountered, caching should be disabled.
For example, --add-subnet=24,96 will add the /24 and /96 subnets
of the requestor for IPv4 and IPv6 requestors, respectively.
--add-subnet=1.2.3.4/24 will add 1.2.3.0/24 for IPv4 requestors
and ::/0 for IPv6 requestors. --add-
subnet=1.2.3.4/24,1.2.3.4/24 will add 1.2.3.0/24 for both IPv4
and IPv6 requestors.
-c, --cache-size=<cachesize>
Set the size of dnsmasq's cache. The default is 150 names.
Setting the cache size to zero disables caching.
-N, --no-negcache
Disable negative caching. Negative caching allows dnsmasq to
remember "no such domain" answers from upstream nameservers and
answer identical queries without forwarding them again.
-0, --dns-forward-max=<queries>
Set the maximum number of concurrent DNS queries. The default
value is 150, which should be fine for most setups. The only
known situation where this needs to be increased is when using
web-server log file resolvers, which can generate large numbers
of concurrent queries.
--dnssec
Validate DNS replies and cache DNSSEC data. When forwarding DNS
queries, dnsmasq requests the DNSSEC records needed to validate
the replies. The replies are validated and the result returned
as the Authenticated Data bit in the DNS packet. In addition the
DNSSEC records are stored in the cache, making validation by
clients more efficient. Note that validation by clients is the
most secure DNSSEC mode, but for clients unable to do
validation, use of the AD bit set by dnsmasq is useful, provided
that the network between the dnsmasq server and the client is
trusted. Dnsmasq must be compiled with HAVE_DNSSEC enabled, and
DNSSEC trust anchors provided, see --trust-anchor. Because the
DNSSEC validation process uses the cache, it is not permitted to
reduce the cache size below the default when DNSSEC is enabled.
The nameservers upstream of dnsmasq must be DNSSEC-capable, ie
capable of returning DNSSEC records with data. If they are not,
then dnsmasq will not be able to determine the trusted status of
answers. In the default mode, this menas that all replies will
be marked as untrusted. If --dnssec-check-unsigned is set and
the upstream servers don't support DNSSEC, then DNS service will
be entirely broken.
--trust-anchor=[<class>],<domain>,<key-tag>,<algorithm>,<digest-
type>,<digest>
Provide DS records to act a trust anchors for DNSSEC validation.
Typically these will be the DS record(s) for Zone Signing key(s)
of the root zone, but trust anchors for limited domains are also
possible. The current root-zone trust anchors may be downloaded
from https://data.iana.org/root-anchors/root-anchors.xml
--dnssec-check-unsigned
As a default, dnsmasq does not check that unsigned DNS replies
are legitimate: they are assumed to be valid and passed on
(without the "authentic data" bit set, of course). This does not
protect against an attacker forging unsigned replies for signed
DNS zones, but it is fast. If this flag is set, dnsmasq will
check the zones of unsigned replies, to ensure that unsigned
replies are allowed in those zones. The cost of this is more
upstream queries and slower performance. See also the warning
about upstream servers in the section on --dnssec
--dnssec-no-timecheck
DNSSEC signatures are only valid for specified time windows, and
should be rejected outside those windows. This generates an
interesting chicken-and-egg problem for machines which don't
have a hardware real time clock. For these machines to determine
the correct time typically requires use of NTP and therefore
DNS, but validating DNS requires that the correct time is
already known. Setting this flag removes the time-window checks
(but not other DNSSEC validation.) only until the dnsmasq
process receives SIGHUP. The intention is that dnsmasq should be
started with this flag when the platform determines that
reliable time is not currently available. As soon as reliable
time is established, a SIGHUP should be sent to dnsmasq, which
enables time checking, and purges the cache of DNS records which
have not been throughly checked.
--dnssec-timestamp=<path>
Enables an alternative way of checking the validity of the
system time for DNSSEC (see --dnssec-no-timecheck). In this
case, the system time is considered to be valid once it becomes
later than the timestamp on the specified file. The file is
created and its timestamp set automatically by dnsmasq. The file
must be stored on a persistent filesystem, so that it and its
mtime are carried over system restarts. The timestamp file is
created after dnsmasq has dropped root, so it must be in a
location writable by the unprivileged user that dnsmasq runs as.
--proxy-dnssec
Copy the DNSSEC Authenticated Data bit from upstream servers to
downstream clients and cache it. This is an alternative to
having dnsmasq validate DNSSEC, but it depends on the security
of the network between dnsmasq and the upstream servers, and the
trustworthiness of the upstream servers.
--dnssec-debug
Set debugging mode for the DNSSEC validation, set the Checking
Disabled bit on upstream queries, and don't convert replies
which do not validate to responses with a return code of
SERVFAIL. Note that setting this may affect DNS behaviour in bad
ways, it is not an extra-logging flag and should not be set in
production.
--auth-zone=<domain>[,<subnet>[/<prefix length>][,<subnet>[/<prefix
length>].....]]
Define a DNS zone for which dnsmasq acts as authoritative
server. Locally defined DNS records which are in the domain will
be served. If subnet(s) are given, A and AAAA records must be in
one of the specified subnets.
As alternative to directly specifying the subnets, it's possible
to give the name of an interface, in which case the subnets
implied by that interface's configured addresses and
netmask/prefix-length are used; this is useful when using
constructed DHCP ranges as the actual address is dynamic and not
known when configuring dnsmasq. The interface addresses may be
confined to only IPv6 addresses using <interface>/6 or to only
IPv4 using <interface>/4. This is useful when an interface has
dynamically determined global IPv6 addresses which should appear
in the zone, but RFC1918 IPv4 addresses which should not.
Interface-name and address-literal subnet specifications may be
used freely in the same --auth-zone declaration.
The subnet(s) are also used to define in-addr.arpa and ip6.arpa
domains which are served for reverse-DNS queries. If not
specified, the prefix length defaults to 24 for IPv4 and 64 for
IPv6. For IPv4 subnets, the prefix length should be have the
value 8, 16 or 24 unless you are familiar with RFC 2317 and have
arranged the in-addr.arpa delegation accordingly. Note that if
no subnets are specified, then no reverse queries are answered.
--auth-soa=<serial>[,<hostmaster>[,<refresh>[,<retry>[,<expiry>]]]]
Specify fields in the SOA record associated with authoritative
zones. Note that this is optional, all the values are set to
sane defaults.
--auth-sec-servers=<domain>[,<domain>[,<domain>...]]
Specify any secondary servers for a zone for which dnsmasq is
authoritative. These servers must be configured to get zone data
from dnsmasq by zone transfer, and answer queries for the same
authoritative zones as dnsmasq.
--auth-peer=<ip-address>[,<ip-address>[,<ip-address>...]]
Specify the addresses of secondary servers which are allowed to
initiate zone transfer (AXFR) requests for zones for which
dnsmasq is authoritative. If this option is not given, then AXFR
requests will be accepted from any secondary.
--conntrack
Read the Linux connection track mark associated with incoming
DNS queries and set the same mark value on upstream traffic used
to answer those queries. This allows traffic generated by
dnsmasq to be associated with the queries which cause it, useful
for bandwidth accounting and firewalling. Dnsmasq must have
conntrack support compiled in and the kernel must have conntrack
support included and configured. This option cannot be combined
with --query-port.
-F, --dhcp-range=[tag:<tag>[,tag:<tag>],][set:<tag>,]<start-
addr>[,<end-addr>|<mode>][,<netmask>[,<broadcast>]][,<lease time>]
-F, --dhcp-range=[tag:<tag>[,tag:<tag>],][set:<tag>,]<start-
IPv6addr>[,<end-IPv6addr>|constructor:<interface>][,<mode>][,<prefix-
len>][,<lease time>]
Enable the DHCP server. Addresses will be given out from the
range <start-addr> to <end-addr> and from statically defined
addresses given in dhcp-host options. If the lease time is
given, then leases will be given for that length of time. The
lease time is in seconds, or minutes (eg 45m) or hours (eg 1h)
or "infinite". If not given, the default lease time is one hour.
The minimum lease time is two minutes. For IPv6 ranges, the
lease time maybe "deprecated"; this sets the preferred lifetime
sent in a DHCP lease or router advertisement to zero, which
causes clients to use other addresses, if available, for new
connections as a prelude to renumbering.
This option may be repeated, with different addresses, to enable
DHCP service to more than one network. For directly connected
networks (ie, networks on which the machine running dnsmasq has
an interface) the netmask is optional: dnsmasq will determine it
from the interface configuration. For networks which receive
DHCP service via a relay agent, dnsmasq cannot determine the
netmask itself, so it should be specified, otherwise dnsmasq
will have to guess, based on the class (A, B or C) of the
network address. The broadcast address is always optional. It is
always allowed to have more than one dhcp-range in a single
subnet.
For IPv6, the parameters are slightly different: instead of
netmask and broadcast address, there is an optional prefix
length which must be equal to or larger then the prefix length
on the local interface. If not given, this defaults to 64.
Unlike the IPv4 case, the prefix length is not automatically
derived from the interface configuration. The mimimum size of
the prefix length is 64.
IPv6 (only) supports another type of range. In this, the start
address and optional end address contain only the network part
(ie ::1) and they are followed by constructor:<interface>. This
forms a template which describes how to create ranges, based on
the addresses assigned to the interface. For instance
--dhcp-range=::1,::400,constructor:eth0
will look for addresses on eth0 and then create a range from
<network>::1 to <network>::400. If the interface is assigned
more than one network, then the corresponding ranges will be
automatically created, and then deprecated and finally removed
again as the address is deprecated and then deleted. The
interface name may have a final "*" wildcard. Note that just any
address on eth0 will not do: it must not be an autoconfigured or
privacy address, or be deprecated.
If a dhcp-range is only being used for stateless DHCP and/or
SLAAC, then the address can be simply ::
--dhcp-range=::,constructor:eth0
The optional set:<tag> sets an alphanumeric label which marks
this network so that dhcp options may be specified on a per-
network basis. When it is prefixed with 'tag:' instead, then
its meaning changes from setting a tag to matching it. Only one
tag may be set, but more than one tag may be matched.
The optional <mode> keyword may be static which tells dnsmasq to
enable DHCP for the network specified, but not to dynamically
allocate IP addresses: only hosts which have static addresses
given via dhcp-host or from /etc/ethers will be served. A
static-only subnet with address all zeros may be used as a
"catch-all" address to enable replies to all Information-request
packets on a subnet which is provided with stateless DHCPv6, ie
--dhcp-range=::,static
For IPv4, the <mode> may be proxy in which case dnsmasq will
provide proxy-DHCP on the specified subnet. (See pxe-prompt and
pxe-service for details.)
For IPv6, the mode may be some combination of ra-only, slaac,
ra-names, ra-stateless, ra-advrouter, off-link.
ra-only tells dnsmasq to offer Router Advertisement only on this
subnet, and not DHCP.
slaac tells dnsmasq to offer Router Advertisement on this subnet
and to set the A bit in the router advertisement, so that the
client will use SLAAC addresses. When used with a DHCP range or
static DHCP address this results in the client having both a
DHCP-assigned and a SLAAC address.
ra-stateless sends router advertisements with the O and A bits
set, and provides a stateless DHCP service. The client will use
a SLAAC address, and use DHCP for other configuration
information.
ra-names enables a mode which gives DNS names to dual-stack
hosts which do SLAAC for IPv6. Dnsmasq uses the host's IPv4
lease to derive the name, network segment and MAC address and
assumes that the host will also have an IPv6 address calculated
using the SLAAC algorithm, on the same network segment. The
address is pinged, and if a reply is received, an AAAA record is
added to the DNS for this IPv6 address. Note that this is only
happens for directly-connected networks, (not one doing DHCP via
a relay) and it will not work if a host is using privacy
extensions. ra-names can be combined with ra-stateless and
slaac.
ra-advrouter enables a mode where router address(es) rather than
prefix(es) are included in the advertisements. This is
described in RFC-3775 section 7.2 and is used in mobile IPv6. In
this mode the interval option is also included, as described in
RFC-3775 section 7.3.
off-link tells dnsmasq to advertise the prefix without the on-
link (aka L) bit set.
-G, --dhcp-
host=[<hwaddr>][,id:<client_id>|*][,set:<tag>][,<ipaddr>][,<hostname>][,<lease_time>][,ignore]
Specify per host parameters for the DHCP server. This allows a
machine with a particular hardware address to be always
allocated the same hostname, IP address and lease time. A
hostname specified like this overrides any supplied by the DHCP
client on the machine. It is also allowable to omit the hardware
address and include the hostname, in which case the IP address
and lease times will apply to any machine claiming that name.
For example --dhcp-host=00:20:e0:3b:13:af,wap,infinite tells
dnsmasq to give the machine with hardware address
00:20:e0:3b:13:af the name wap, and an infinite DHCP lease.
--dhcp-host=lap,192.168.0.199 tells dnsmasq to always allocate
the machine lap the IP address 192.168.0.199.
Addresses allocated like this are not constrained to be in the
range given by the --dhcp-range option, but they must be in the
same subnet as some valid dhcp-range. For subnets which don't
need a pool of dynamically allocated addresses, use the "static"
keyword in the dhcp-range declaration.
It is allowed to use client identifiers (called client DUID in
IPv6-land rather than hardware addresses to identify hosts by
prefixing with 'id:'. Thus: --dhcp-host=id:01:02:03:04,.....
refers to the host with client identifier 01:02:03:04. It is
also allowed to specify the client ID as text, like this:
--dhcp-host=id:clientidastext,.....
A single dhcp-host may contain an IPv4 address or an IPv6
address, or both. IPv6 addresses must be bracketed by square
brackets thus: --dhcp-host=laptop,[1234::56] IPv6 addresses may
contain only the host-identifier part: --dhcp-host=laptop,[::56]
in which case they act as wildcards in constructed dhcp ranges,
with the appropriate network part inserted. Note that in IPv6
DHCP, the hardware address may not be available, though it
normally is for direct-connected clients, or clients using DHCP
relays which support RFC 6939.
For DHCPv4, the special option id:* means "ignore any client-id
and use MAC addresses only." This is useful when a client
presents a client-id sometimes but not others.
If a name appears in /etc/hosts, the associated address can be
allocated to a DHCP lease, but only if a --dhcp-host option
specifying the name also exists. Only one hostname can be given
in a dhcp-host option, but aliases are possible by using CNAMEs.
(See --cname ).
The special keyword "ignore" tells dnsmasq to never offer a DHCP
lease to a machine. The machine can be specified by hardware
address, client ID or hostname, for instance --dhcp-
host=00:20:e0:3b:13:af,ignore This is useful when there is
another DHCP server on the network which should be used by some
machines.
The set:<tag> construct sets the tag whenever this dhcp-host
directive is in use. This can be used to selectively send DHCP
options just for this host. More than one tag can be set in a
dhcp-host directive (but not in other places where "set:<tag>"
is allowed). When a host matches any dhcp-host directive (or one
implied by /etc/ethers) then the special tag "known" is set.
This allows dnsmasq to be configured to ignore requests from
unknown machines using --dhcp-ignore=tag:!known Ethernet
addresses (but not client-ids) may have wildcard bytes, so for
example --dhcp-host=00:20:e0:3b:13:*,ignore will cause dnsmasq
to ignore a range of hardware addresses. Note that the "*" will
need to be escaped or quoted on a command line, but not in the
configuration file.
Hardware addresses normally match any network (ARP) type, but it
is possible to restrict them to a single ARP type by preceding
them with the ARP-type (in HEX) and "-". so --dhcp-
host=06-00:20:e0:3b:13:af,1.2.3.4 will only match a Token-Ring
hardware address, since the ARP-address type for token ring is
6.
As a special case, in DHCPv4, it is possible to include more
than one hardware address. eg: --dhcp-
host=11:22:33:44:55:66,12:34:56:78:90:12,192.168.0.2 This allows
an IP address to be associated with multiple hardware addresses,
and gives dnsmasq permission to abandon a DHCP lease to one of
the hardware addresses when another one asks for a lease. Beware
that this is a dangerous thing to do, it will only work reliably
if only one of the hardware addresses is active at any time and
there is no way for dnsmasq to enforce this. It is, for
instance, useful to allocate a stable IP address to a laptop
which has both wired and wireless interfaces.
--dhcp-hostsfile=<path>
Read DHCP host information from the specified file. If a
directory is given, then read all the files contained in that
directory. The file contains information about one host per
line. The format of a line is the same as text to the right of
'=' in --dhcp-host. The advantage of storing DHCP host
information in this file is that it can be changed without re-
starting dnsmasq: the file will be re-read when dnsmasq receives
SIGHUP.
--dhcp-optsfile=<path>
Read DHCP option information from the specified file. If a
directory is given, then read all the files contained in that
directory. The advantage of using this option is the same as for
--dhcp-hostsfile: the dhcp-optsfile will be re-read when dnsmasq
receives SIGHUP. Note that it is possible to encode the
information in a
--dhcp-hostsdir=<path>
This is equivalent to dhcp-hostsfile, except for the following.
The path MUST be a directory, and not an individual file.
Changed or new files within the directory are read
automatically, without the need to send SIGHUP. If a file is
deleted for changed after it has been read by dnsmasq, then the
host record it contained will remain until dnsmasq recieves a
SIGHUP, or is restarted; ie host records are only added
dynamically.
--dhcp-optsdir=<path>
This is equivalent to dhcp-optsfile, with the differences noted
for --dhcp-hostsdir.
--dhcp-boot
flag as DHCP options, using the options names bootfile-name,
server-ip-address and tftp-server. This allows these to be
included in a dhcp-optsfile.
-Z, --read-ethers
Read /etc/ethers for information about hosts for the DHCP
server. The format of /etc/ethers is a hardware address,
followed by either a hostname or dotted-quad IP address. When
read by dnsmasq these lines have exactly the same effect as
--dhcp-host options containing the same information. /etc/ethers
is re-read when dnsmasq receives SIGHUP. IPv6 addresses are NOT
read from /etc/ethers.
-O, --dhcp-option=[tag:<tag>,[tag:<tag>,]][encap:<opt>,][vi-
encap:<enterprise>,][vendor:[<vendor-class>],][<opt>|option:<opt-
name>|option6:<opt>|option6:<opt-name>],[<value>[,<value>]]
Specify different or extra options to DHCP clients. By default,
dnsmasq sends some standard options to DHCP clients, the netmask
and broadcast address are set to the same as the host running
dnsmasq, and the DNS server and default route are set to the
address of the machine running dnsmasq. (Equivalent rules apply
for IPv6.) If the domain name option has been set, that is sent.
This configuration allows these defaults to be overridden, or
other options specified. The option, to be sent may be given as
a decimal number or as "option:<option-name>" The option numbers
are specified in RFC2132 and subsequent RFCs. The set of option-
names known by dnsmasq can be discovered by running "dnsmasq
--help dhcp". For example, to set the default route option to
192.168.4.4, do --dhcp-option=3,192.168.4.4 or --dhcp-option =
option:router, 192.168.4.4 and to set the time-server address to
192.168.0.4, do --dhcp-option = 42,192.168.0.4 or --dhcp-option
= option:ntp-server, 192.168.0.4 The special address 0.0.0.0 is
taken to mean "the address of the machine running dnsmasq".
Data types allowed are comma separated dotted-quad IPv4
addresses, []-wrapped IPv6 addresses, a decimal number, colon-
separated hex digits and a text string. If the optional tags are
given then this option is only sent when all the tags are
matched.
Special processing is done on a text argument for option 119, to
conform with RFC 3397. Text or dotted-quad IP addresses as
arguments to option 120 are handled as per RFC 3361. Dotted-quad
IP addresses which are followed by a slash and then a netmask
size are encoded as described in RFC 3442.
IPv6 options are specified using the option6: keyword, followed
by the option number or option name. The IPv6 option name space
is disjoint from the IPv4 option name space. IPv6 addresses in
options must be bracketed with square brackets, eg. --dhcp-
option=option6:ntp-server,[1234::56] For IPv6, [::] means "the
global address of the machine running dnsmasq", whilst [fd00::]
is replaced with the ULA, if it exists, and [fe80::] with the
link-local address.
Be careful: no checking is done that the correct type of data
for the option number is sent, it is quite possible to persuade
dnsmasq to generate illegal DHCP packets with injudicious use of
this flag. When the value is a decimal number, dnsmasq must
determine how large the data item is. It does this by examining
the option number and/or the value, but can be overridden by
appending a single letter flag as follows: b = one byte, s = two
bytes, i = four bytes. This is mainly useful with encapsulated
vendor class options (see below) where dnsmasq cannot determine
data size from the option number. Option data which consists
solely of periods and digits will be interpreted by dnsmasq as
an IP address, and inserted into an option as such. To force a
literal string, use quotes. For instance when using option 66 to
send a literal IP address as TFTP server name, it is necessary
to do --dhcp-option=66,"1.2.3.4"
Encapsulated Vendor-class options may also be specified (IPv4
only) using --dhcp-option: for instance --dhcp-
option=vendor:PXEClient,1,0.0.0.0 sends the encapsulated vendor
class-specific option "mftp-address=0.0.0.0" to any client whose
vendor-class matches "PXEClient". The vendor-class matching is
substring based (see --dhcp-vendorclass for details). If a
vendor-class option (number 60) is sent by dnsmasq, then that is
used for selecting encapsulated options in preference to any
sent by the client. It is possible to omit the vendorclass
completely; --dhcp-option=vendor:,1,0.0.0.0 in which case the
encapsulated option is always sent.
Options may be encapsulated (IPv4 only) within other options:
for instance --dhcp-option=encap:175, 190, iscsi-client0 will
send option 175, within which is the option 190. If multiple
options are given which are encapsulated with the same option
number then they will be correctly combined into one
encapsulated option. encap: and vendor: are may not both be set
in the same dhcp-option.
The final variant on encapsulated options is "Vendor-Identifying
Vendor Options" as specified by RFC3925. These are denoted like
this: --dhcp-option=vi-encap:2, 10, text The number in the vi-
encap: section is the IANA enterprise number used to identify
this option. This form of encapsulation is supported in IPv6.
The address 0.0.0.0 is not treated specially in encapsulated
options.
--dhcp-option-force=[tag:<tag>,[tag:<tag>,]][encap:<opt>,][vi-
encap:<enterprise>,][vendor:[<vendor-class>],]<opt>,[<value>[,<value>]]
This works in exactly the same way as --dhcp-option except that
the option will always be sent, even if the client does not ask
for it in the parameter request list. This is sometimes needed,
for example when sending options to PXELinux.
--dhcp-no-override
(IPv4 only) Disable re-use of the DHCP servername and filename
fields as extra option space. If it can, dnsmasq moves the boot
server and filename information (from dhcp-boot) out of their
dedicated fields into DHCP options. This make extra space
available in the DHCP packet for options but can, rarely,
confuse old or broken clients. This flag forces "simple and
safe" behaviour to avoid problems in such a case.
--dhcp-relay=<local address>,<server address>[,<interface]
Configure dnsmasq to do DHCP relay. The local address is an
address allocated to an interface on the host running dnsmasq.
All DHCP requests arriving on that interface will we relayed to
a remote DHCP server at the server address. It is possible to
relay from a single local address to multiple remote servers by
using multiple dhcp-relay configs with the same local address
and different server addresses. A server address must be an IP
literal address, not a domain name. In the case of DHCPv6, the
server address may be the ALL_SERVERS multicast address,
ff05::1:3. In this case the interface must be given, not be
wildcard, and is used to direct the multicast to the correct
interface to reach the DHCP server.
Access control for DHCP clients has the same rules as for the
DHCP server, see --interface, --except-interface, etc. The
optional interface name in the dhcp-relay config has a different
function: it controls on which interface DHCP replies from the
server will be accepted. This is intended for configurations
which have three interfaces: one being relayed from, a second
connecting the DHCP server, and a third untrusted network,
typically the wider internet. It avoids the possibility of spoof
replies arriving via this third interface.
It is allowed to have dnsmasq act as a DHCP server on one set of
interfaces and relay from a disjoint set of interfaces. Note
that whilst it is quite possible to write configurations which
appear to act as a server and a relay on the same interface,
this is not supported: the relay function will take precedence.
Both DHCPv4 and DHCPv6 relay is supported. It's not possible to
relay DHCPv4 to a DHCPv6 server or vice-versa.
-U, --dhcp-vendorclass=set:<tag>,[enterprise:<IANA-enterprise
number>,]<vendor-class>
Map from a vendor-class string to a tag. Most DHCP clients
provide a "vendor class" which represents, in some sense, the
type of host. This option maps vendor classes to tags, so that
DHCP options may be selectively delivered to different classes
of hosts. For example dhcp-vendorclass=set:printers,Hewlett-
Packard JetDirect will allow options to be set only for HP
printers like so: --dhcp-option=tag:printers,3,192.168.4.4 The
vendor-class string is substring matched against the vendor-
class supplied by the client, to allow fuzzy matching. The set:
prefix is optional but allowed for consistency.
Note that in IPv6 only, vendorclasses are namespaced with an
IANA-allocated enterprise number. This is given with enterprise:
keyword and specifies that only vendorclasses matching the
specified number should be searched.
-j, --dhcp-userclass=set:<tag>,<user-class>
Map from a user-class string to a tag (with substring matching,
like vendor classes). Most DHCP clients provide a "user class"
which is configurable. This option maps user classes to tags, so
that DHCP options may be selectively delivered to different
classes of hosts. It is possible, for instance to use this to
set a different printer server for hosts in the class "accounts"
than for hosts in the class "engineering".
-4, --dhcp-mac=set:<tag>,<MAC address>
Map from a MAC address to a tag. The MAC address may include
wildcards. For example --dhcp-mac=set:3com,01:34:23:*:*:* will
set the tag "3com" for any host whose MAC address matches the
pattern.
--dhcp-circuitid=set:<tag>,<circuit-id>, --dhcp-
remoteid=set:<tag>,<remote-id>
Map from RFC3046 relay agent options to tags. This data may be
provided by DHCP relay agents. The circuit-id or remote-id is
normally given as colon-separated hex, but is also allowed to be
a simple string. If an exact match is achieved between the
circuit or agent ID and one provided by a relay agent, the tag
is set.
dhcp-remoteid (but not dhcp-circuitid) is supported in IPv6.
--dhcp-subscrid=set:<tag>,<subscriber-id>
(IPv4 and IPv6) Map from RFC3993 subscriber-id relay agent
options to tags.
--dhcp-proxy[=<ip addr>]......
(IPv4 only) A normal DHCP relay agent is only used to forward
the initial parts of a DHCP interaction to the DHCP server. Once
a client is configured, it communicates directly with the
server. This is undesirable if the relay agent is adding extra
information to the DHCP packets, such as that used by dhcp-
circuitid and dhcp-remoteid. A full relay implementation can
use the RFC 5107 serverid-override option to force the DHCP
server to use the relay as a full proxy, with all packets
passing through it. This flag provides an alternative method of
doing the same thing, for relays which don't support RFC 5107.
Given alone, it manipulates the server-id for all interactions
via relays. If a list of IP addresses is given, only
interactions via relays at those addresses are affected.
--dhcp-match=set:<tag>,<option number>|option:<option name>|vi-
encap:<enterprise>[,<value>]
Without a value, set the tag if the client sends a DHCP option
of the given number or name. When a value is given, set the tag
only if the option is sent and matches the value. The value may
be of the form "01:ff:*:02" in which case the value must match
(apart from wildcards) but the option sent may have unmatched
data past the end of the value. The value may also be of the
same form as in dhcp-option in which case the option sent is
treated as an array, and one element must match, so
--dhcp-match=set:efi-ia32,option:client-arch,6
will set the tag "efi-ia32" if the the number 6 appears in the
list of architectures sent by the client in option 93. (See RFC
4578 for details.) If the value is a string, substring matching
is used.
The special form with vi-encap:<enterprise number> matches
against vendor-identifying vendor classes for the specified
enterprise. Please see RFC 3925 for more details of these rare
and interesting beasts.
--tag-if=set:<tag>[,set:<tag>[,tag:<tag>[,tag:<tag>]]]
Perform boolean operations on tags. Any tag appearing as
set:<tag> is set if all the tags which appear as tag:<tag> are
set, (or unset when tag:!<tag> is used) If no tag:<tag> appears
set:<tag> tags are set unconditionally. Any number of set: and
tag: forms may appear, in any order. Tag-if lines ares executed
in order, so if the tag in tag:<tag> is a tag set by another
tag-if, the line which sets the tag must precede the one which
tests it.
-J, --dhcp-ignore=tag:<tag>[,tag:<tag>]
When all the given tags appear in the tag set ignore the host
and do not allocate it a DHCP lease.
--dhcp-ignore-names[=tag:<tag>[,tag:<tag>]]
When all the given tags appear in the tag set, ignore any
hostname provided by the host. Note that, unlike dhcp-ignore, it
is permissible to supply no tags, in which case DHCP-client
supplied hostnames are always ignored, and DHCP hosts are added
to the DNS using only dhcp-host configuration in dnsmasq and the
contents of /etc/hosts and /etc/ethers.
--dhcp-generate-names=tag:<tag>[,tag:<tag>]
(IPv4 only) Generate a name for DHCP clients which do not
otherwise have one, using the MAC address expressed in hex,
separated by dashes. Note that if a host provides a name, it
will be used by preference to this, unless --dhcp-ignore-names
is set.
--dhcp-broadcast[=tag:<tag>[,tag:<tag>]]
(IPv4 only) When all the given tags appear in the tag set,
always use broadcast to communicate with the host when it is
unconfigured. It is permissible to supply no tags, in which case
this is unconditional. Most DHCP clients which need broadcast
replies set a flag in their requests so that this happens
automatically, some old BOOTP clients do not.
-M, --dhcp-boot=[tag:<tag>,]<filename>,[<servername>[,<server
address>|<tftp_servername>]]
(IPv4 only) Set BOOTP options to be returned by the DHCP server.
Server name and address are optional: if not provided, the name
is left empty, and the address set to the address of the machine
running dnsmasq. If dnsmasq is providing a TFTP service (see
--enable-tftp ) then only the filename is required here to
enable network booting. If the optional tag(s) are given, they
must match for this configuration to be sent. Instead of an IP
address, the TFTP server address can be given as a domain name
which is looked up in /etc/hosts. This name can be associated in
/etc/hosts with multiple IP addresses, which are used round-
robin. This facility can be used to load balance the tftp load
among a set of servers.
--dhcp-sequential-ip
Dnsmasq is designed to choose IP addresses for DHCP clients
using a hash of the client's MAC address. This normally allows a
client's address to remain stable long-term, even if the client
sometimes allows its DHCP lease to expire. In this default mode
IP addresses are distributed pseudo-randomly over the entire
available address range. There are sometimes circumstances
(typically server deployment) where it is more convenient to
have IP addresses allocated sequentially, starting from the
lowest available address, and setting this flag enables this
mode. Note that in the sequential mode, clients which allow a
lease to expire are much more likely to move IP address; for
this reason it should not be generally used.
--pxe-service=[tag:<tag>,]<CSA>,<menu
text>[,<basename>|<bootservicetype>][,<server address>|<server_name>]
Most uses of PXE boot-ROMS simply allow the PXE system to obtain
an IP address and then download the file specified by dhcp-boot
and execute it. However the PXE system is capable of more
complex functions when supported by a suitable DHCP server.
This specifies a boot option which may appear in a PXE boot
menu. <CSA> is client system type, only services of the correct
type will appear in a menu. The known types are x86PC, PC98,
IA64_EFI, Alpha, Arc_x86, Intel_Lean_Client, IA32_EFI,
X86-64_EFI, Xscale_EFI, BC_EFI, ARM32_EFI and ARM64_EFI; an
integer may be used for other types. The parameter after the
menu text may be a file name, in which case dnsmasq acts as a
boot server and directs the PXE client to download the file by
TFTP, either from itself ( enable-tftp must be set for this to
work) or another TFTP server if the final server address/name is
given. Note that the "layer" suffix (normally ".0") is supplied
by PXE, and need not be added to the basename. Alternatively,
the basename may be a filename, complete with suffix, in which
case no layer suffix is added. If an integer boot service type,
rather than a basename is given, then the PXE client will search
for a suitable boot service for that type on the network. This
search may be done by broadcast, or direct to a server if its IP
address/name is provided. If no boot service type or filename
is provided (or a boot service type of 0 is specified) then the
menu entry will abort the net boot procedure and continue
booting from local media. The server address can be given as a
domain name which is looked up in /etc/hosts. This name can be
associated in /etc/hosts with multiple IP addresses, which are
used round-robin.
--pxe-prompt=[tag:<tag>,]<prompt>[,<timeout>]
Setting this provides a prompt to be displayed after PXE boot.
If the timeout is given then after the timeout has elapsed with
no keyboard input, the first available menu option will be
automatically executed. If the timeout is zero then the first
available menu item will be executed immediately. If pxe-prompt
is omitted the system will wait for user input if there are
multiple items in the menu, but boot immediately if there is
only one. See pxe-service for details of menu items.
Dnsmasq supports PXE "proxy-DHCP", in this case another DHCP
server on the network is responsible for allocating IP
addresses, and dnsmasq simply provides the information given in
pxe-prompt and pxe-service to allow netbooting. This mode is
enabled using the proxy keyword in dhcp-range.
-X, --dhcp-lease-max=<number>
Limits dnsmasq to the specified maximum number of DHCP leases.
The default is 1000. This limit is to prevent DoS attacks from
hosts which create thousands of leases and use lots of memory in
the dnsmasq process.
-K, --dhcp-authoritative
Should be set when dnsmasq is definitely the only DHCP server on
a network. For DHCPv4, it changes the behaviour from strict RFC
compliance so that DHCP requests on unknown leases from unknown
hosts are not ignored. This allows new hosts to get a lease
without a tedious timeout under all circumstances. It also
allows dnsmasq to rebuild its lease database without each client
needing to reacquire a lease, if the database is lost. For
DHCPv6 it sets the priority in replies to 255 (the maximum)
instead of 0 (the minimum).
--dhcp-alternate-port[=<server port>[,<client port>]]
(IPv4 only) Change the ports used for DHCP from the default. If
this option is given alone, without arguments, it changes the
ports used for DHCP from 67 and 68 to 1067 and 1068. If a single
argument is given, that port number is used for the server and
the port number plus one used for the client. Finally, two port
numbers allows arbitrary specification of both server and client
ports for DHCP.
-3, --bootp-dynamic[=<network-id>[,<network-id>]]
(IPv4 only) Enable dynamic allocation of IP addresses to BOOTP
clients. Use this with care, since each address allocated to a
BOOTP client is leased forever, and therefore becomes
permanently unavailable for re-use by other hosts. if this is
given without tags, then it unconditionally enables dynamic
allocation. With tags, only when the tags are all set. It may be
repeated with different tag sets.
-5, --no-ping
(IPv4 only) By default, the DHCP server will attempt to ensure
that an address is not in use before allocating it to a host. It
does this by sending an ICMP echo request (aka "ping") to the
address in question. If it gets a reply, then the address must
already be in use, and another is tried. This flag disables this
check. Use with caution.
--log-dhcp
Extra logging for DHCP: log all the options sent to DHCP clients
and the tags used to determine them.
--quiet-dhcp, --quiet-dhcp6, --quiet-ra
Suppress logging of the routine operation of these protocols.
Errors and problems will still be logged. --quiet-dhcp and
quiet-dhcp6 are over-ridden by --log-dhcp.
-l, --dhcp-leasefile=<path>
Use the specified file to store DHCP lease information.
--dhcp-duid=<enterprise-id>,<uid>
(IPv6 only) Specify the server persistent UID which the DHCPv6
server will use. This option is not normally required as dnsmasq
creates a DUID automatically when it is first needed. When
given, this option provides dnsmasq the data required to create
a DUID-EN type DUID. Note that once set, the DUID is stored in
the lease database, so to change between DUID-EN and
automatically created DUIDs or vice-versa, the lease database
must be re-intialised. The enterprise-id is assigned by IANA,
and the uid is a string of hex octets unique to a particular
device.
-6 --dhcp-script=<path>
Whenever a new DHCP lease is created, or an old one destroyed,
or a TFTP file transfer completes, the executable specified by
this option is run. <path> must be an absolute pathname, no
PATH search occurs. The arguments to the process are "add",
"old" or "del", the MAC address of the host (or DUID for IPv6) ,
the IP address, and the hostname, if known. "add" means a lease
has been created, "del" means it has been destroyed, "old" is a
notification of an existing lease when dnsmasq starts or a
change to MAC address or hostname of an existing lease (also,
lease length or expiry and client-id, if leasefile-ro is set).
If the MAC address is from a network type other than ethernet,
it will have the network type prepended, eg
"06-01:23:45:67:89:ab" for token ring. The process is run as
root (assuming that dnsmasq was originally run as root) even if
dnsmasq is configured to change UID to an unprivileged user.
The environment is inherited from the invoker of dnsmasq, with
some or all of the following variables added
For both IPv4 and IPv6:
DNSMASQ_DOMAIN if the fully-qualified domain name of the host is
known, this is set to the domain part. (Note that the hostname
passed to the script as an argument is never fully-qualified.)
If the client provides a hostname, DNSMASQ_SUPPLIED_HOSTNAME
If the client provides user-classes,
DNSMASQ_USER_CLASS0..DNSMASQ_USER_CLASSn
If dnsmasq was compiled with HAVE_BROKEN_RTC, then the length of
the lease (in seconds) is stored in DNSMASQ_LEASE_LENGTH,
otherwise the time of lease expiry is stored in
DNSMASQ_LEASE_EXPIRES. The number of seconds until lease expiry
is always stored in DNSMASQ_TIME_REMAINING.
If a lease used to have a hostname, which is removed, an "old"
event is generated with the new state of the lease, ie no name,
and the former name is provided in the environment variable
DNSMASQ_OLD_HOSTNAME.
DNSMASQ_INTERFACE stores the name of the interface on which the
request arrived; this is not set for "old" actions when dnsmasq
restarts.
DNSMASQ_RELAY_ADDRESS is set if the client used a DHCP relay to
contact dnsmasq and the IP address of the relay is known.
DNSMASQ_TAGS contains all the tags set during the DHCP
transaction, separated by spaces.
DNSMASQ_LOG_DHCP is set if --log-dhcp is in effect.
For IPv4 only:
DNSMASQ_CLIENT_ID if the host provided a client-id.
DNSMASQ_CIRCUIT_ID, DNSMASQ_SUBSCRIBER_ID, DNSMASQ_REMOTE_ID if
a DHCP relay-agent added any of these options.
If the client provides vendor-class, DNSMASQ_VENDOR_CLASS.
For IPv6 only:
If the client provides vendor-class, DNSMASQ_VENDOR_CLASS_ID,
containing the IANA enterprise id for the class, and
DNSMASQ_VENDOR_CLASS0..DNSMASQ_VENDOR_CLASSn for the data.
DNSMASQ_SERVER_DUID containing the DUID of the server: this is
the same for every call to the script.
DNSMASQ_IAID containing the IAID for the lease. If the lease is
a temporary allocation, this is prefixed to 'T'.
DNSMASQ_MAC containing the MAC address of the client, if known.
Note that the supplied hostname, vendorclass and userclass data
is only supplied for "add" actions or "old" actions when a host
resumes an existing lease, since these data are not held in
dnsmasq's lease database.
All file descriptors are closed except stdin, stdout and stderr
which are open to /dev/null (except in debug mode).
The script is not invoked concurrently: at most one instance of
the script is ever running (dnsmasq waits for an instance of
script to exit before running the next). Changes to the lease
database are which require the script to be invoked are queued
awaiting exit of a running instance. If this queueing allows
multiple state changes occur to a single lease before the script
can be run then earlier states are discarded and the current
state of that lease is reflected when the script finally runs.
At dnsmasq startup, the script will be invoked for all existing
leases as they are read from the lease file. Expired leases will
be called with "del" and others with "old". When dnsmasq
receives a HUP signal, the script will be invoked for existing
leases with an "old" event.
There are four further actions which may appear as the first
argument to the script, "init", "arp-add", "arp-del" and "tftp".
More may be added in the future, so scripts should be written to
ignore unknown actions. "init" is described below in
--leasefile-ro The "tftp" action is invoked when a TFTP file
transfer completes: the arguments are the file size in bytes,
the address to which the file was sent, and the complete
pathname of the file.
The "arp-add" and "arp-del" actions are only called if enabled
with --script-arp They are are supplied with a MAC address and
IP address as arguments. "arp-add" indicates the arrival of a
new entry in the ARP or neighbour table, and "arp-del" indicates
the deletion of same.
--dhcp-luascript=<path>
Specify a script written in Lua, to be run when leases are
created, destroyed or changed. To use this option, dnsmasq must
be compiled with the correct support. The Lua interpreter is
intialised once, when dnsmasq starts, so that global variables
persist between lease events. The Lua code must define a lease
function, and may provide init and shutdown functions, which are
called, without arguments when dnsmasq starts up and terminates.
It may also provide a tftp function.
The lease function receives the information detailed in --dhcp-
script. It gets two arguments, firstly the action, which is a
string containing, "add", "old" or "del", and secondly a table
of tag value pairs. The tags mostly correspond to the
environment variables detailed above, for instance the tag
"domain" holds the same data as the environment variable
DNSMASQ_DOMAIN. There are a few extra tags which hold the data
supplied as arguments to --dhcp-script. These are mac_address,
ip_address and hostname for IPv4, and client_duid, ip_address
and hostname for IPv6.
The tftp function is called in the same way as the lease
function, and the table holds the tags destination_address,
file_name and file_size.
The arp and arp-old functions are called only when enabled with
--script-arp and have a table which holds the tags mac_addres
and client_address.
--dhcp-scriptuser
Specify the user as which to run the lease-change script or Lua
script. This defaults to root, but can be changed to another
user using this flag.
--script-arp
Enable the "arp" and "arp-old" functions in the dhcp-script and
dhcp-luascript.
-9, --leasefile-ro
Completely suppress use of the lease database file. The file
will not be created, read, or written. Change the way the lease-
change script (if one is provided) is called, so that the lease
database may be maintained in external storage by the script. In
addition to the invocations given in --dhcp-script the lease-
change script is called once, at dnsmasq startup, with the
single argument "init". When called like this the script should
write the saved state of the lease database, in dnsmasq
leasefile format, to stdout and exit with zero exit code.
Setting this option also forces the leasechange script to be
called on changes to the client-id and lease length and expiry
time.
--bridge-interface=<interface>,<alias>[,<alias>]
Treat DHCP (v4 and v6) request and IPv6 Router Solicit packets
arriving at any of the <alias> interfaces as if they had arrived
at <interface>. This option allows dnsmasq to provide DHCP and
RA service over unaddressed and unbridged Ethernet interfaces,
e.g. on an OpenStack compute host where each such interface is a
TAP interface to a VM, or as in "old style bridging" on BSD
platforms. A trailing '*' wildcard can be used in each <alias>.
-s, --domain=<domain>[,<address range>[,local]]
Specifies DNS domains for the DHCP server. Domains may be be
given unconditionally (without the IP range) or for limited IP
ranges. This has two effects; firstly it causes the DHCP server
to return the domain to any hosts which request it, and secondly
it sets the domain which it is legal for DHCP-configured hosts
to claim. The intention is to constrain hostnames so that an
untrusted host on the LAN cannot advertise its name via dhcp as
e.g. "microsoft.com" and capture traffic not meant for it. If no
domain suffix is specified, then any DHCP hostname with a domain
part (ie with a period) will be disallowed and logged. If suffix
is specified, then hostnames with a domain part are allowed,
provided the domain part matches the suffix. In addition, when a
suffix is set then hostnames without a domain part have the
suffix added as an optional domain part. Eg on my network I can
set --domain=thekelleys.org.uk and have a machine whose DHCP
hostname is "laptop". The IP address for that machine is
available from dnsmasq both as "laptop" and
"laptop.thekelleys.org.uk". If the domain is given as "#" then
the domain is read from the first "search" directive in
/etc/resolv.conf (or equivalent).
The address range can be of the form <ip address>,<ip address>
or <ip address>/<netmask> or just a single <ip address>. See
--dhcp-fqdn which can change the behaviour of dnsmasq with
domains.
If the address range is given as ip-address/network-size, then a
additional flag "local" may be supplied which has the effect of
adding --local declarations for forward and reverse DNS queries.
Eg. --domain=thekelleys.org.uk,192.168.0.0/24,local is
identical to --domain=thekelleys.org.uk,192.168.0.0/24
--local=/thekelleys.org.uk/ --local=/0.168.192.in-addr.arpa/ The
network size must be 8, 16 or 24 for this to be legal.
--dhcp-fqdn
In the default mode, dnsmasq inserts the unqualified names of
DHCP clients into the DNS. For this reason, the names must be
unique, even if two clients which have the same name are in
different domains. If a second DHCP client appears which has the
same name as an existing client, the name is transferred to the
new client. If --dhcp-fqdn is set, this behaviour changes: the
unqualified name is no longer put in the DNS, only the qualified
name. Two DHCP clients with the same name may both keep the
name, provided that the domain part is different (ie the fully
qualified names differ.) To ensure that all names have a domain
part, there must be at least --domain without an address
specified when --dhcp-fqdn is set.
--dhcp-client-update
Normally, when giving a DHCP lease, dnsmasq sets flags in the
FQDN option to tell the client not to attempt a DDNS update with
its name and IP address. This is because the name-IP pair is
automatically added into dnsmasq's DNS view. This flag
suppresses that behaviour, this is useful, for instance, to
allow Windows clients to update Active Directory servers. See
RFC 4702 for details.
--enable-ra
Enable dnsmasq's IPv6 Router Advertisement feature. DHCPv6
doesn't handle complete network configuration in the same way as
DHCPv4. Router discovery and (possibly) prefix discovery for
autonomous address creation are handled by a different protocol.
When DHCP is in use, only a subset of this is needed, and
dnsmasq can handle it, using existing DHCP configuration to
provide most data. When RA is enabled, dnsmasq will advertise a
prefix for each dhcp-range, with default router as the relevant
link-local address on the machine running dnsmasq. By default,
the "managed address" bits are set, and the "use SLAAC" bit is
reset. This can be changed for individual subnets with the mode
keywords described in --dhcp-range. RFC6106 DNS parameters are
included in the advertisements. By default, the relevant link-
local address of the machine running dnsmasq is sent as
recursive DNS server. If provided, the DHCPv6 options dns-server
and domain-search are used for the DNS server (RDNSS) and the
domain serach list (DNSSL).
--ra-param=<interface>,[high|low],[[<ra-interval>],<router lifetime>]
Set non-default values for router advertisements sent via an
interface. The priority field for the router may be altered from
the default of medium with eg --ra-param=eth0,high. The
interval between router advertisements may be set (in seconds)
with --ra-param=eth0,60. The lifetime of the route may be
changed or set to zero, which allows a router to advertise
prefixes but not a route via itself. --ra-parm=eth0,0,0 (A
value of zero for the interval means the default value.) All
three parameters may be set at once. --ra-param=low,60,1200 The
interface field may include a wildcard.
--enable-tftp[=<interface>[,<interface>]]
Enable the TFTP server function. This is deliberately limited to
that needed to net-boot a client. Only reading is allowed; the
tsize and blksize extensions are supported (tsize is only
supported in octet mode). Without an argument, the TFTP service
is provided to the same set of interfaces as DHCP service. If
the list of interfaces is provided, that defines which
interfaces recieve TFTP service.
--tftp-root=<directory>[,<interface>]
Look for files to transfer using TFTP relative to the given
directory. When this is set, TFTP paths which include ".." are
rejected, to stop clients getting outside the specified root.
Absolute paths (starting with /) are allowed, but they must be
within the tftp-root. If the optional interface argument is
given, the directory is only used for TFTP requests via that
interface.
--tftp-no-fail
Do not abort startup if specified tftp root directories are
inaccessible.
--tftp-unique-root
Add the IP address of the TFTP client as a path component on the
end of the TFTP-root (in standard dotted-quad format). Only
valid if a tftp-root is set and the directory exists. For
instance, if tftp-root is "/tftp" and client 1.2.3.4 requests
file "myfile" then the effective path will be
"/tftp/1.2.3.4/myfile" if /tftp/1.2.3.4 exists or /tftp/myfile
otherwise.
--tftp-secure
Enable TFTP secure mode: without this, any file which is
readable by the dnsmasq process under normal unix access-control
rules is available via TFTP. When the --tftp-secure flag is
given, only files owned by the user running the dnsmasq process
are accessible. If dnsmasq is being run as root, different rules
apply: --tftp-secure has no effect, but only files which have
the world-readable bit set are accessible. It is not recommended
to run dnsmasq as root with TFTP enabled, and certainly not
without specifying --tftp-root. Doing so can expose any world-
readable file on the server to any host on the net.
--tftp-lowercase
Convert filenames in TFTP requests to all lowercase. This is
useful for requests from Windows machines, which have case-
insensitive filesystems and tend to play fast-and-loose with
case in filenames. Note that dnsmasq's tftp server always
converts "\" to "/" in filenames.
--tftp-max=<connections>
Set the maximum number of concurrent TFTP connections allowed.
This defaults to 50. When serving a large number of TFTP
connections, per-process file descriptor limits may be
encountered. Dnsmasq needs one file descriptor for each
concurrent TFTP connection and one file descriptor per unique
file (plus a few others). So serving the same file
simultaneously to n clients will use require about n + 10 file
descriptors, serving different files simultaneously to n clients
will require about (2*n) + 10 descriptors. If --tftp-port-range
is given, that can affect the number of concurrent connections.
--tftp-mtu=<mtu size>
Use size as the ceiling of the MTU supported by the intervening
network when negotiating TFTP blocksize, overriding the MTU
setting of the local interface if it is larger.
--tftp-no-blocksize
Stop the TFTP server from negotiating the "blocksize" option
with a client. Some buggy clients request this option but then
behave badly when it is granted.
--tftp-port-range=<start>,<end>
A TFTP server listens on a well-known port (69) for connection
initiation, but it also uses a dynamically-allocated port for
each connection. Normally these are allocated by the OS, but
this option specifies a range of ports for use by TFTP
transfers. This can be useful when TFTP has to traverse a
firewall. The start of the range cannot be lower than 1025
unless dnsmasq is running as root. The number of concurrent TFTP
connections is limited by the size of the port range.
-C, --conf-file=<file>
Specify a different configuration file. The conf-file option is
also allowed in configuration files, to include multiple
configuration files. A filename of "-" causes dnsmasq to read
configuration from stdin.
-7, --conf-dir=<directory>[,<file-extension>......],
Read all the files in the given directory as configuration
files. If extension(s) are given, any files which end in those
extensions are skipped. Any files whose names end in ~ or start
with . or start and end with # are always skipped. If the
extension starts with * then only files which have that
extension are loaded. So --conf-dir=/path/to/dir,*.conf loads
all files with the suffix .conf in /path/to/dir. This flag may
be given on the command line or in a configuration file. If
giving it on the command line, be sure to escape * characters.
--servers-file=<file>
A special case of --conf-file which differs in two respects.
Firstly, only --server and --rev-server are allowed in the
configuration file included. Secondly, the file is re-read and
the configuration therein is updated when dnsmasq recieves
SIGHUP.
CONFIG FILE
At startup, dnsmasq reads /etc/dnsmasq.conf, if it exists. (On FreeBSD, the file is /usr/local/etc/dnsmasq.conf ) (but see the -C and -7 options.) The format of this file consists of one option per line, exactly as the long options detailed in the OPTIONS section but without the leading "--". Lines starting with # are comments and ignored. For options which may only be specified once, the configuration file overrides the command line. Quoting is allowed in a config file: between " quotes the special meanings of ,:. and # are removed and the following escapes are allowed: \\ \" \t \e \r and \n. The later corresponding to tab, escape, backspace, return and newline.
NOTES
When it receives a SIGHUP, dnsmasq clears its cache and then re-loads /etc/hosts and /etc/ethers and any file given by --dhcp-hostsfile, --dhcp-hostsdir, --dhcp-optsfile, --dhcp-optsdir, --addn-hosts or --hostsdir. The dhcp lease change script is called for all existing DHCP leases. If --no-poll is set SIGHUP also re-reads /etc/resolv.conf. SIGHUP does NOT re-read the configuration file. When it receives a SIGUSR1, dnsmasq writes statistics to the system log. It writes the cache size, the number of names which have had to removed from the cache before they expired in order to make room for new names and the total number of names that have been inserted into the cache. The number of cache hits and misses and the number of authoritative queries answered are also given. For each upstream server it gives the number of queries sent, and the number which resulted in an error. In --no-daemon mode or when full logging is enabled (-q), a complete dump of the contents of the cache is made. The cache statistics are also available in the DNS as answers to queries of class CHAOS and type TXT in domain bind. The domain names are cachesize.bind, insertions.bind, evictions.bind, misses.bind, hits.bind, auth.bind and servers.bind. An example command to query this, using the dig utility would be dig +short chaos txt cachesize.bind When it receives SIGUSR2 and it is logging direct to a file (see --log- facility ) dnsmasq will close and reopen the log file. Note that during this operation, dnsmasq will not be running as root. When it first creates the logfile dnsmasq changes the ownership of the file to the non-root user it will run as. Logrotate should be configured to create a new log file with the ownership which matches the existing one before sending SIGUSR2. If TCP DNS queries are in progress, the old logfile will remain open in child processes which are handling TCP queries and may continue to be written. There is a limit of 150 seconds, after which all existing TCP processes will have expired: for this reason, it is not wise to configure logfile compression for logfiles which have just been rotated. Using logrotate, the required options are create and delaycompress. Dnsmasq is a DNS query forwarder: it it not capable of recursively answering arbitrary queries starting from the root servers but forwards such queries to a fully recursive upstream DNS server which is typically provided by an ISP. By default, dnsmasq reads /etc/resolv.conf to discover the IP addresses of the upstream nameservers it should use, since the information is typically stored there. Unless --no-poll is used, dnsmasq checks the modification time of /etc/resolv.conf (or equivalent if --resolv-file is used) and re- reads it if it changes. This allows the DNS servers to be set dynamically by PPP or DHCP since both protocols provide the information. Absence of /etc/resolv.conf is not an error since it may not have been created before a PPP connection exists. Dnsmasq simply keeps checking in case /etc/resolv.conf is created at any time. Dnsmasq can be told to parse more than one resolv.conf file. This is useful on a laptop, where both PPP and DHCP may be used: dnsmasq can be set to poll both /etc/ppp/resolv.conf and /etc/dhcpc/resolv.conf and will use the contents of whichever changed last, giving automatic switching between DNS servers. Upstream servers may also be specified on the command line or in the configuration file. These server specifications optionally take a domain name which tells dnsmasq to use that server only to find names in that particular domain. In order to configure dnsmasq to act as cache for the host on which it is running, put "nameserver 127.0.0.1" in /etc/resolv.conf to force local processes to send queries to dnsmasq. Then either specify the upstream servers directly to dnsmasq using --server options or put their addresses real in another file, say /etc/resolv.dnsmasq and run dnsmasq with the -r /etc/resolv.dnsmasq option. This second technique allows for dynamic update of the server addresses by PPP or DHCP. Addresses in /etc/hosts will "shadow" different addresses for the same names in the upstream DNS, so "mycompany.com 1.2.3.4" in /etc/hosts will ensure that queries for "mycompany.com" always return 1.2.3.4 even if queries in the upstream DNS would otherwise return a different address. There is one exception to this: if the upstream DNS contains a CNAME which points to a shadowed name, then looking up the CNAME through dnsmasq will result in the unshadowed address associated with the target of the CNAME. To work around this, add the CNAME to /etc/hosts so that the CNAME is shadowed too. The tag system works as follows: For each DHCP request, dnsmasq collects a set of valid tags from active configuration lines which include set:<tag>, including one from the dhcp-range used to allocate the address, one from any matching dhcp-host (and "known" if a dhcp- host matches) The tag "bootp" is set for BOOTP requests, and a tag whose name is the name of the interface on which the request arrived is also set. Any configuration lines which include one or more tag:<tag> constructs will only be valid if all that tags are matched in the set derived above. Typically this is dhcp-option. dhcp-option which has tags will be used in preference to an untagged dhcp-option, provided that _all_ the tags match somewhere in the set collected as described above. The prefix '!' on a tag means 'not' so --dhcp-option=tag:!purple,3,1.2.3.4 sends the option when the tag purple is not in the set of valid tags. (If using this in a command line rather than a configuration file, be sure to escape !, which is a shell metacharacter) When selecting dhcp-options, a tag from dhcp-range is second class relative to other tags, to make it easy to override options for individual hosts, so dhcp-range=set:interface1,...... dhcp- host=set:myhost,..... dhcp-option=tag:interface1,option:nis- domain,"domain1" dhcp-option=tag:myhost,option:nis-domain,"domain2" will set the NIS-domain to domain1 for hosts in the range, but override that to domain2 for a particular host. Note that for dhcp-range both tag:<tag> and set:<tag> are allowed, to both select the range in use based on (eg) dhcp-host, and to affect the options sent, based on the range selected. This system evolved from an earlier, more limited one and for backward compatibility "net:" may be used instead of "tag:" and "set:" may be omitted. (Except in dhcp-host, where "net:" may be used instead of "set:".) For the same reason, '#' may be used instead of '!' to indicate NOT. The DHCP server in dnsmasq will function as a BOOTP server also, provided that the MAC address and IP address for clients are given, either using dhcp-host configurations or in /etc/ethers , and a dhcp- range configuration option is present to activate the DHCP server on a particular network. (Setting --bootp-dynamic removes the need for static address mappings.) The filename parameter in a BOOTP request is used as a tag, as is the tag "bootp", allowing some control over the options returned to different classes of hosts.
AUTHORITATIVE CONFIGURATION
Configuring dnsmasq to act as an authoritative DNS server is
complicated by the fact that it involves configuration of external DNS
servers to provide delegation. We will walk through three scenarios of
increasing complexity. Prerequisites for all of these scenarios are a
globally accessible IP address, an A or AAAA record pointing to that
address, and an external DNS server capable of doing delegation of the
zone in question. For the first part of this explanation, we will call
the A (or AAAA) record for the globally accessible address
server.example.com, and the zone for which dnsmasq is authoritative
our.zone.com.
The simplest configuration consists of two lines of dnsmasq
configuration; something like
auth-server=server.example.com,eth0
auth-zone=our.zone.com,1.2.3.0/24
and two records in the external DNS
server.example.com A 192.0.43.10
our.zone.com NS server.example.com
eth0 is the external network interface on which dnsmasq is listening,
and has (globally accessible) address 192.0.43.10.
Note that the external IP address may well be dynamic (ie assigned from
an ISP by DHCP or PPP) If so, the A record must be linked to this
dynamic assignment by one of the usual dynamic-DNS systems.
A more complex, but practically useful configuration has the address
record for the globally accessible IP address residing in the
authoritative zone which dnsmasq is serving, typically at the root. Now
we have
auth-server=our.zone.com,eth0
auth-zone=our.zone.com,1.2.3.0/24
our.zone.com A 1.2.3.4
our.zone.com NS our.zone.com
The A record for our.zone.com has now become a glue record, it solves
the chicken-and-egg problem of finding the IP address of the nameserver
for our.zone.com when the A record is within that zone. Note that this
is the only role of this record: as dnsmasq is now authoritative from
our.zone.com it too must provide this record. If the external address
is static, this can be done with an /etc/hosts entry or --host-record.
auth-server=our.zone.com,eth0
host-record=our.zone.com,1.2.3.4
auth-zone=our.zone.com,1.2.3.0/24
If the external address is dynamic, the address associated with
our.zone.com must be derived from the address of the relevant
interface. This is done using interface-name Something like:
auth-server=our.zone.com,eth0
interface-name=our.zone.com,eth0
auth-zone=our.zone.com,1.2.3.0/24,eth0
(The "eth0" argument in auth-zone adds the subnet containing eth0's
dynamic address to the zone, so that the interface-name returns the
address in outside queries.)
Our final configuration builds on that above, but also adds a secondary
DNS server. This is another DNS server which learns the DNS data for
the zone by doing zones transfer, and acts as a backup should the
primary server become inaccessible. The configuration of the secondary
is beyond the scope of this man-page, but the extra configuration of
dnsmasq is simple:
auth-sec-servers=secondary.myisp.com
and
our.zone.com NS secondary.myisp.com
Adding auth-sec-servers enables zone transfer in dnsmasq, to allow the
secondary to collect the DNS data. If you wish to restrict this data to
particular hosts then
auth-peer=<IP address of secondary>
will do so.
Dnsmasq acts as an authoritative server for in-addr.arpa and ip6.arpa
domains associated with the subnets given in auth-zone declarations, so
reverse (address to name) lookups can be simply configured with a
suitable NS record, for instance in this example, where we allow
1.2.3.0/24 addresses.
3.2.1.in-addr.arpa NS our.zone.com
Note that at present, reverse (in-addr.arpa and ip6.arpa) zones are not
available in zone transfers, so there is no point arranging secondary
servers for reverse lookups.
When dnsmasq is configured to act as an authoritative server, the
following data is used to populate the authoritative zone.
--mx-host, --srv-host, --dns-rr, --txt-record, --naptr-record , as long
as the record names are in the authoritative domain.
--cname as long as the record name is in the authoritative domain. If
the target of the CNAME is unqualified, then it is qualified with the
authoritative zone name.
IPv4 and IPv6 addresses from /etc/hosts (and --addn-hosts ) and --host-
record and --interface-name provided the address falls into one of the
subnets specified in the --auth-zone.
Addresses of DHCP leases, provided the address falls into one of the
subnets specified in the --auth-zone. (If contructed DHCP ranges are
is use, which depend on the address dynamically assigned to an
interface, then the form of --auth-zone which defines subnets by the
dynamic address of an interface should be used to ensure this condition
is met.)
In the default mode, where a DHCP lease has an unqualified name, and
possibly a qualified name constructed using --domain then the name in
the authoritative zone is constructed from the unqualified name and the
zone's domain. This may or may not equal that specified by --domain.
If --dhcp-fqdn is set, then the fully qualified names associated with
DHCP leases are used, and must match the zone's domain.
EXIT CODES
0 - Dnsmasq successfully forked into the background, or terminated normally if backgrounding is not enabled. 1 - A problem with configuration was detected. 2 - A problem with network access occurred (address in use, attempt to use privileged ports without permission). 3 - A problem occurred with a filesystem operation (missing file/directory, permissions). 4 - Memory allocation failure. 5 - Other miscellaneous problem. 11 or greater - a non zero return code was received from the lease- script process "init" call. The exit code from dnsmasq is the script's exit code with 10 added.
LIMITS
The default values for resource limits in dnsmasq are generally conservative, and appropriate for embedded router type devices with slow processors and limited memory. On more capable hardware, it is possible to increase the limits, and handle many more clients. The following applies to dnsmasq-2.37: earlier versions did not scale as well. Dnsmasq is capable of handling DNS and DHCP for at least a thousand clients. The DHCP lease times should not be very short (less than one hour). The value of --dns-forward-max can be increased: start with it equal to the number of clients and increase if DNS seems slow. Note that DNS performance depends too on the performance of the upstream nameservers. The size of the DNS cache may be increased: the hard limit is 10000 names and the default (150) is very low. Sending SIGUSR1 to dnsmasq makes it log information which is useful for tuning the cache size. See the NOTES section for details. The built-in TFTP server is capable of many simultaneous file transfers: the absolute limit is related to the number of file-handles allowed to a process and the ability of the select() system call to cope with large numbers of file handles. If the limit is set too high using --tftp-max it will be scaled down and the actual limit logged at start-up. Note that more transfers are possible when the same file is being sent than when each transfer sends a different file. It is possible to use dnsmasq to block Web advertising by using a list of known banner-ad servers, all resolving to 127.0.0.1 or 0.0.0.0, in /etc/hosts or an additional hosts file. The list can be very long, dnsmasq has been tested successfully with one million names. That size file needs a 1GHz processor and about 60Mb of RAM.
INTERNATIONALISATION
Dnsmasq can be compiled to support internationalisation. To do this, the make targets "all-i18n" and "install-i18n" should be used instead of the standard targets "all" and "install". When internationalisation is compiled in, dnsmasq will produce log messages in the local language and support internationalised domain names (IDN). Domain names in /etc/hosts, /etc/ethers and /etc/dnsmasq.conf which contain non-ASCII characters will be translated to the DNS-internal punycode representation. Note that dnsmasq determines both the language for messages and the assumed charset for configuration files from the LANG environment variable. This should be set to the system default value by the script which is responsible for starting dnsmasq. When editing the configuration files, be careful to do so using only the system-default locale and not user-specific one, since dnsmasq has no direct way of determining the charset in use, and must assume that it is the system default.
FILES
/etc/dnsmasq.conf /usr/local/etc/dnsmasq.conf /etc/resolv.conf /var/run/dnsmasq/resolv.conf /etc/ppp/resolv.conf /etc/dhcpc/resolv.conf /etc/hosts /etc/ethers /var/lib/misc/dnsmasq.leases /var/db/dnsmasq.leases /var/run/dnsmasq.pid
SEE ALSO
hosts(5), resolver(5)
AUTHOR
This manual page was written by Simon Kelley <simon@thekelleys.org.uk>.
DNSMASQ(8)
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