ARPWATCH(8)ARPWATCH(8)NAME
arpwatch - keep track of ethernet/ip address pairings
SYNOPSIS
arpwatch [ -dNw ] [ -f datafile ] [ -i interface ]
[ -n net[/width ]] [ -r file ] [ -u username ] [ -e username ]
[ -s 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 net‐
mask for the network's class is used.
The -N flag disables reporting any bogons.
The -w flag is used to specify an interface without a valid IPv4
address.
The -r flag is used to specify a savefile (perhaps created by tcp‐
dump(1) or pcapture(1)) to read from instead of reading from the net‐
work. 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 security reasons.
If the -e flag is used, arpwatch sends e-mail messages to username
rather than the default (root). If a single `-' character is given for
the username, sending of e-mail is suppressed, but logging via syslog
is still done as usual. (This can be useful during initial runs, to
collect data without being flooded with messages about new stations.)
If the -s flag is used, arpwatch sends e-mail messages with username as
the return address, rather than the default (root).
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.
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 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 ALSOarpsnmp(8), arp(8), bpf(4), tcpdump(1), pcapture(1), pcap(3)AUTHORS
Craig Leres of the Lawrence Berkeley National Laboratory Network Re‐
search 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.
4th Berkeley Distribution 8 October 2000 ARPWATCH(8)
