ip-route - routing table management


   ip [ ip-OPTIONS ] route  { COMMAND | help }

   ip route { list | flush } SELECTOR

   ip route save SELECTOR

   ip route restore

   ip route get ADDRESS [ from ADDRESS iif STRING  ] [ oif STRING ] [ tos
           TOS ]

   ip route { add | del | change | append | replace } ROUTE

   SELECTOR := [ root PREFIX ] [ match PREFIX ] [ exact PREFIX ] [ table
           TABLE_ID ] [ proto RTPROTO ] [ type TYPE ] [ scope SCOPE ]


   NODE_SPEC := [ TYPE ] PREFIX [ tos TOS ] [ table TABLE_ID ] [ proto
           RTPROTO ] [ scope SCOPE ] [ metric METRIC ]

   INFO_SPEC := NH OPTIONS FLAGS [ nexthop NH ] ...

   NH := [ via [ FAMILY ] ADDRESS ] [ dev STRING ] [ weight NUMBER ]

   FAMILY := [ inet | inet6 | ipx | dnet | mpls | bridge | link ]

   OPTIONS := FLAGS [ mtu NUMBER ] [ advmss NUMBER ] [ as [ to ] ADDRESS ]
           rtt TIME ] [ rttvar TIME ] [ reordering NUMBER ] [ window
           NUMBER ] [ cwnd NUMBER ] [ ssthresh REALM ] [ realms REALM ] [
           rto_min TIME ] [ initcwnd NUMBER ] [ initrwnd NUMBER ] [
           features FEATURES ] [ quickack BOOL ] [ congctl NAME ] pref
           PREF ]

   TYPE := [ unicast | local | broadcast | multicast | throw | unreachable
           | prohibit | blackhole | nat ]

   TABLE_ID := [ local| main | default | all | NUMBER ]

   SCOPE := [ host | link | global | NUMBER ]

   NHFLAGS := [ onlink | pervasive ]

   RTPROTO := [ kernel | boot | static | NUMBER ]

   FEATURES := [ ecn | ]

   PREF := [ low | medium | high ]


   ip route is used to manipulate entries in the kernel routing tables.

   Route types:

           unicast - the route entry describes real paths to the
           destinations covered by the route prefix.

           unreachable - these destinations are unreachable. Packets are
           discarded and the ICMP message host unreachable is generated.
           The local senders get an EHOSTUNREACH error.

           blackhole - these destinations are unreachable. Packets are
           discarded silently.  The local senders get an EINVAL error.

           prohibit - these destinations are unreachable. Packets are
           discarded and the ICMP message communication administratively
           prohibited is generated. The local senders get an EACCES error.

           local - the destinations are assigned to this host. The packets
           are looped back and delivered locally.

           broadcast - the destinations are broadcast addresses. The
           packets are sent as link broadcasts.

           throw - a special control route used together with policy
           rules. If such a route is selected, lookup in this table is
           terminated pretending that no route was found. Without policy
           routing it is equivalent to the absence of the route in the
           routing table. The packets are dropped and the ICMP message net
           unreachable is generated. The local senders get an ENETUNREACH

           nat - a special NAT route. Destinations covered by the prefix
           are considered to be dummy (or external) addresses which
           require translation to real (or internal) ones before
           forwarding. The addresses to translate to are selected with the
           attribute via.  Warning: Route NAT is no longer supported in
           Linux 2.6.

           anycast - not implemented the destinations are anycast
           addresses assigned to this host. They are mainly equivalent to
           local with one difference: such addresses are invalid when used
           as the source address of any packet.

           multicast - a special type used for multicast routing. It is
           not present in normal routing tables.

   Route tables: Linux-2.x can pack routes into several routing tables
   identified by a number in the range from 1 to 2^31 or by name from the
   file /etc/iproute2/rt_tables By default all normal routes are inserted
   into the main table (ID 254) and the kernel only uses this table when
   calculating routes.  Values (0, 253, 254, and 255) are reserved for
   built-in use.

   Actually, one other table always exists, which is invisible but even
   more important. It is the local table (ID 255). This table consists of
   routes for local and broadcast addresses. The kernel maintains this
   table automatically and the administrator usually need not modify it or
   even look at it.

   The multiple routing tables enter the game when policy routing is used.

   ip route add
          add new route

   ip route change
          change route

   ip route replace
          change or add new one

          to TYPE PREFIX (default)
                 the destination prefix of the route. If TYPE is omitted,
                 ip assumes type unicast.  Other values of TYPE are listed
                 above.  PREFIX is an IP or IPv6 address optionally
                 followed by a slash and the prefix length. If the length
                 of the prefix is missing, ip assumes a full-length host
                 route. There is also a special PREFIX default - which is
                 equivalent to IP 0/0 or to IPv6 ::/0.

          tos TOS

          dsfield TOS
                 the Type Of Service (TOS) key. This key has no associated
                 mask and the longest match is understood as: First,
                 compare the TOS of the route and of the packet. If they
                 are not equal, then the packet may still match a route
                 with a zero TOS.  TOS is either an 8 bit hexadecimal
                 number or an identifier from /etc/iproute2/rt_dsfield.

          metric NUMBER

          preference NUMBER
                 the preference value of the route.  NUMBER is an
                 arbitrary 32bit number.

          table TABLEID
                 the table to add this route to.  TABLEID may be a number
                 or a string from the file /etc/iproute2/rt_tables.  If
                 this parameter is omitted, ip assumes the main table,
                 with the exception of local, broadcast and nat routes,
                 which are put into the local table by default.

          dev NAME
                 the output device name.

          via [ FAMILY ] ADDRESS
                 the address of the nexthop router, in the address family
                 FAMILY.  Actually, the sense of this field depends on the
                 route type.  For normal unicast routes it is either the
                 true next hop router or, if it is a direct route
                 installed in BSD compatibility mode, it can be a local
                 address of the interface. For NAT routes it is the first
                 address of the block of translated IP destinations.

          src ADDRESS
                 the source address to prefer when sending to the
                 destinations covered by the route prefix.

          realm REALMID
                 the realm to which this route is assigned.  REALMID may
                 be a number or a string from the file

          mtu MTU

          mtu lock MTU
                 the MTU along the path to the destination. If the
                 modifier lock is not used, the MTU may be updated by the
                 kernel due to Path MTU Discovery. If the modifier lock is
                 used, no path MTU discovery will be tried, all packets
                 will be sent without the DF bit in IPv4 case or
                 fragmented to MTU for IPv6.

          window NUMBER
                 the maximal window for TCP to advertise to these
                 destinations, measured in bytes. It limits maximal data
                 bursts that our TCP peers are allowed to send to us.

          rtt TIME
                 the initial RTT ('Round Trip Time') estimate. If no
                 suffix is specified the units are raw values passed
                 directly to the routing code to maintain compatibility
                 with previous releases.  Otherwise if a suffix of s, sec
                 or secs is used to specify seconds and ms, msec or msecs
                 to specify milliseconds.

          rttvar TIME (2.3.15+ only)
                 the initial RTT variance estimate. Values are specified
                 as with rtt above.

          rto_min TIME (2.6.23+ only)
                 the minimum TCP Retransmission TimeOut to use when
                 communicating with this destination. Values are specified
                 as with rtt above.

          ssthresh NUMBER (2.3.15+ only)
                 an estimate for the initial slow start threshold.

          cwnd NUMBER (2.3.15+ only)
                 the clamp for congestion window. It is ignored if the
                 lock flag is not used.

          initcwnd NUMBER (2.5.70+ only)
                 the initial congestion window size for connections to
                 this destination.  Actual window size is this value
                 multiplied by the MSS (``Maximal Segment Size'') for same
                 connection. The default is zero, meaning to use the
                 values specified in RFC2414.

          initrwnd NUMBER (2.6.33+ only)
                 the initial receive window size for connections to this
                 destination.  Actual window size is this value multiplied
                 by the MSS of the connection.  The default value is zero,
                 meaning to use Slow Start value.

          features FEATURES (3.18+only)
                 Enable or disable per-route features. Only available
                 feature at this time is ecn to enable explicit congestion
                 notification when initiating connections to the given
                 destination network.  When responding to a connection
                 request from the given network, ecn will also be used
                 even if the net.ipv4.tcp_ecn sysctl is set to 0.

          quickack BOOL (3.11+ only)
                 Enable or disable quick ack for connections to this

          congctl NAME (3.20+ only)

          congctl lock NAME (3.20+ only)
                 Sets a specific TCP congestion control algorithm only for
                 a given destination.  If not specified, Linux keeps the
                 current global default TCP congestion control algorithm,
                 or the one set from the application. If the modifier lock
                 is not used, an application may nevertheless overwrite
                 the suggested congestion control algorithm for that
                 destination. If the modifier lock is used, then an
                 application is not allowed to overwrite the specified
                 congestion control algorithm for that destination, thus
                 it will be enforced/guaranteed to use the proposed

          advmss NUMBER (2.3.15+ only)
                 the MSS ('Maximal Segment Size') to advertise to these
                 destinations when establishing TCP connections. If it is
                 not given, Linux uses a default value calculated from the
                 first hop device MTU.  (If the path to these destination
                 is asymmetric, this guess may be wrong.)

          reordering NUMBER (2.3.15+ only)
                 Maximal reordering on the path to this destination.  If
                 it is not given, Linux uses the value selected with
                 sysctl variable net/ipv4/tcp_reordering.

          nexthop NEXTHOP
                 the nexthop of a multipath route.  NEXTHOP is a complex
                 value with its own syntax similar to the top level
                 argument lists:

                         via [ FAMILY ] ADDRESS - is the nexthop router.

                         dev NAME - is the output device.

                         weight NUMBER - is a weight for this element of a
                         multipath route reflecting its relative bandwidth
                         or quality.

          scope SCOPE_VAL
                 the scope of the destinations covered by the route
                 prefix.  SCOPE_VAL may be a number or a string from the
                 file /etc/iproute2/rt_scopes.  If this parameter is
                 omitted, ip assumes scope global for all gatewayed
                 unicast routes, scope link for direct unicast and
                 broadcast routes and scope host for local routes.

          protocol RTPROTO
                 the routing protocol identifier of this route.  RTPROTO
                 may be a number or a string from the file
                 /etc/iproute2/rt_protos.  If the routing protocol ID is
                 not given, ip assumes protocol boot (i.e. it assumes the
                 route was added by someone who doesn't understand what
                 they are doing). Several protocol values have a fixed
                 interpretation.  Namely:

                         redirect - the route was installed due to an ICMP

                         kernel - the route was installed by the kernel
                         during autoconfiguration.

                         boot - the route was installed during the bootup
                         sequence.  If a routing daemon starts, it will
                         purge all of them.

                         static - the route was installed by the
                         administrator to override dynamic routing.
                         Routing daemon will respect them and, probably,
                         even advertise them to its peers.

                         ra - the route was installed by Router Discovery

                 The rest of the values are not reserved and the
                 administrator is free to assign (or not to assign)
                 protocol tags.

          onlink pretend that the nexthop is directly attached to this
                 link, even if it does not match any interface prefix.

          pref PREF
                 the IPv6 route preference.  PREF is a string specifying
                 the route preference as defined in RFC4191 for Router
                 Discovery messages. Namely:

                         low - the route has a lowest priority

                         medium - the route has a default priority

                         high - the route has a highest priority

   ip route delete
          delete route
          ip route del has the same arguments as ip route add, but their
          semantics are a bit different.

          Key values (to, tos, preference and table) select the route to
          delete. If optional attributes are present, ip verifies that
          they coincide with the attributes of the route to delete.  If no
          route with the given key and attributes was found, ip route del

   ip route show
          list routes
          the command displays the contents of the routing tables or the
          route(s) selected by some criteria.

          to SELECTOR (default)
                 only select routes from the given range of destinations.
                 SELECTOR consists of an optional modifier (root, match or
                 exact) and a prefix.  root PREFIX selects routes with
                 prefixes not shorter than PREFIX.  F.e.  root 0/0 selects
                 the entire routing table.  match PREFIX selects routes
                 with prefixes not longer than PREFIX.  F.e.  match
                 10.0/16 selects 10.0/16, 10/8 and 0/0, but it does not
                 select 10.1/16 and 10.0.0/24.  And exact PREFIX (or just
                 PREFIX) selects routes with this exact prefix. If neither
                 of these options are present, ip assumes root 0/0 i.e. it
                 lists the entire table.

          tos TOS

          dsfield TOS
                 only select routes with the given TOS.

          table TABLEID
                 show the routes from this table(s). The default setting
                 is to show table main.  TABLEID may either be the ID of a
                 real table or one of the special values:

                         all - list all of the tables.

                         cache - dump the routing cache.


          cached list cloned routes i.e. routes which were dynamically
                 forked from other routes because some route attribute
                 (f.e. MTU) was updated.  Actually, it is equivalent to
                 table cache.

          from SELECTOR
                 the same syntax as for to, but it binds the source
                 address range rather than destinations.  Note that the
                 from option only works with cloned routes.

          protocol RTPROTO
                 only list routes of this protocol.

          scope SCOPE_VAL
                 only list routes with this scope.

          type TYPE
                 only list routes of this type.

          dev NAME
                 only list routes going via this device.

          via [ FAMILY ] PREFIX
                 only list routes going via the nexthop routers selected
                 by PREFIX.

          src PREFIX
                 only list routes with preferred source addresses selected
                 by PREFIX.

          realm REALMID

          realms FROMREALM/TOREALM
                 only list routes with these realms.

   ip route flush
          flush routing tables
          this command flushes routes selected by some criteria.

          The arguments have the same syntax and semantics as the
          arguments of ip route show, but routing tables are not listed
          but purged. The only difference is the default action: show
          dumps all the IP main routing table but flush prints the helper

          With the -statistics option, the command becomes verbose. It
          prints out the number of deleted routes and the number of rounds
          made to flush the routing table. If the option is given twice,
          ip route flush also dumps all the deleted routes in the format
          described in the previous subsection.

   ip route get
          get a single route
          this command gets a single route to a destination and prints its
          contents exactly as the kernel sees it.

          to ADDRESS (default)
                 the destination address.

          from ADDRESS
                 the source address.

          tos TOS

          dsfield TOS
                 the Type Of Service.

          iif NAME
                 the device from which this packet is expected to arrive.

          oif NAME
                 force the output device on which this packet will be

                 if no source address (option from) was given, relookup
                 the route with the source set to the preferred address
                 received from the first lookup.  If policy routing is
                 used, it may be a different route.

          Note that this operation is not equivalent to ip route show.
          show shows existing routes.  get resolves them and creates new
          clones if necessary. Essentially, get is equivalent to sending a
          packet along this path.  If the iif argument is not given, the
          kernel creates a route to output packets towards the requested
          destination.  This is equivalent to pinging the destination with
          a subsequent ip route ls cache, however, no packets are actually
          sent. With the iif argument, the kernel pretends that a packet
          arrived from this interface and searches for a path to forward
          the packet.

   ip route save
          save routing table information to stdout
          This command behaves like ip route show except that the output
          is raw data suitable for passing to ip route restore.

   ip route restore
          restore routing table information from stdin
          This command expects to read a data stream as returned from ip
          route save.  It will attempt to restore the routing table
          information exactly as it was at the time of the save, so any
          translation of information in the stream (such as device
          indexes) must be done first. Any existing routes are left
          unchanged. Any routes specified in the data stream that already
          exist in the table will be ignored.


   ip ro
       Show all route entries in the kernel.

   ip route add default via dev eth0
       Adds a default route (for all addresses) via the local gateway that can be reached on device eth0.




   Original Manpage by Michail Litvak <mci@owl.openwall.com>


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