arpwatch - keep track of ethernet/ip address pairings
SYNOPSIS
arpwatch [ -dN ] [ -f datafile ] [ -i interface ]
[ -n net[/width ]] [ -r file ] [ -u username ]
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 net
work'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.
If -u flag is used, arpwatch drops root privileges and
changes user ID to username and group ID to that of the
primary group of username. This is recommended for secu
rity reasons.
Note that an empty arp.dat file must be created before the
first time you run arpwatch. Also, the default directory
(where arp.dat is stored) must be owned by username if -u
flag is used.
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.
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 sup
pressed.)
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
/usr/operator/arpwatch - default directory
arp.dat - ethernet/ip address database
ethercodes.dat - vendor ethernet block list
SEE ALSO
arpsnmp(8), arp(8), bpf(4), tcpdump(1), pcapture(1),
pcap(3)
Craig Leres of the Lawrence Berkeley National Laboratory
Network Research Group, University of California, Berke
ley, 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.
Man(1) output converted with
man2html