arpwatch(8)
NAME
arpwatch - keep track of ethernet/ip address pairings
SYNOPSIS
arpwatch [ -dN ]
[ -f datafile ]
[ -i interface ]
[ -n net[/width ]]
[ -r file ]
[ -s sendmail_path ]
[ -p ]
[ -a ]
[ -m addr ]
[ -u username ]
[ -R seconds ]
[ -Q ]
[ -z ignorenet/ignoremask ]
DESCRIPTION
Arpwatch keeps track for ethernet/ip address pairings. It syslogs activity and reports certain changes via email. Arpwatch uses pcap(3) to listen for arp packets on a local ethernet interface. The -d flag is used enable debugging. This also inhibits forking into the background and emailing the reports. Instead, they are sent to stderr. The -f flag is used to set the ethernet/ip address database filename. The default is arp.dat. The -i flag is used to override the default interface. The -n flag specifies additional local networks. This can be useful to avoid "bogon" warnings when there is more than one network running on the same wire. If the optional width is not specified, the default netmask for the network's class is used. The -N flag disables reporting any bogons. The -r flag is used to specify a savefile (perhaps created by tcpdump(1) or pcapture(1)) to read from instead of reading from the network. In this case, arpwatch does not fork. (Debian) The -s flag is used to specify the path to the sendmail program. Any program that takes the option -odi and then text from stdin can be substituted. This is useful for redirecting reports to log files instead of mail. (Debian) The -p flag disables promiscuous operation. ARP broadcasts get through hubs without having the interface in promiscuous mode, while saving considerable resources that would be wasted on processing gigabytes of non-broadcast traffic. OTOH, setting promiscuous mode does not mean getting 100% traffic that would concern arpwatch . YMMV. (Debian) -a By default, arpwatch reports bogons (unless -N is given) for IP addresses that are in the same subnet than the first IP address of the default interface. If this option is specified, arpwatch will report bogons about every IP addresses. (Debian) The -m option is used to specify the e-mail address to which reports will be sent. By default, reports are sent to root on the local machine. (Debian) The -u flag instructs arpwatch to drop root privileges and change the UID to username and GID to the primary group of username . This is recommended for security reasons, but username has to have write access to the default directory. (Debian) The -R flag instructs arpwatch to restart in seconds seconds after the interface went down. By default, in such cases arpwatch would print an error message and exit. This option is ignored if either the -r or -u flags are used. (Debian) The -Q flags prevents arpwatch from sending reports by mail. (Debian) The -z flag is used to set a range of ip addresses to ignore (such as a DHCP range). Netmask is specified as 255.255.128.0. Note that an empty arp.dat file must be created before the first time you run arpwatch.
REPORT MESSAGES
Here's a quick list of the report messages generated by arpwatch(1)
(and arpsnmp(1)):
new activity
This ethernet/ip address pair has been used for the first time
six months or more.
new station
The ethernet address has not been seen before.
flip flop
The ethernet address has changed from the most recently seen
address to the second most recently seen address. (If either
the old or new ethernet address is a DECnet address and it is
less than 24 hours, the email version of the report is
suppressed.)
changed ethernet address
The host switched to a new ethernet address.
SYSLOG MESSAGES
Here are some of the syslog messages; note that messages that are
reported are also sysloged.
ethernet broadcast
The mac ethernet address of the host is a broadcast address.
ip broadcast
The ip address of the host is a broadcast address.
bogon The source ip address is not local to the local subnet.
ethernet broadcast
The source mac or arp ethernet address was all ones or all
zeros.
ethernet mismatch
The source mac ethernet address didn't match the address inside
the arp packet.
reused old ethernet address
The ethernet address has changed from the most recently seen
address to the third (or greater) least recently seen address.
(This is similar to a flip flop.)
suppressed DECnet flip flop
A "flip flop" report was suppressed because one of the two
addresses was a DECnet address.
FILES
/var/lib/arpwatch - default directory arp.dat - ethernet/ip address database /usr/share/arpwatch/ethercodes.dat - vendor ethernet block list
SEE ALSO
arpsnmp(8), arp(8), bpf(4), tcpdump(1), pcapture(1), pcap(3)
AUTHORS
Craig Leres of the Lawrence Berkeley National Laboratory Network
Research Group, University of California, Berkeley, CA.
The current version is available via anonymous ftp:
ftp://ftp.ee.lbl.gov/arpwatch.tar.gz
BUGS
Please send bug reports to arpwatch@ee.lbl.gov. Attempts are made to suppress DECnet flip flops but they aren't always successful. Most error messages are posted using syslog.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
