ARPWATCH(8)						      System Manager's Manual						       ARPWATCH(8)

NAME

       arpwatch - keep track of ethernet/ip address pairings

SYNOPSIS

       arpwatch [ -dN ] [ -f datafile ] [ -i interface ]
		[ -n net[/width ]] [ -r file ] [ -u username ] [ -e username ] [ -s username ]

DESCRIPTION

       Arpwatch keeps track for MAC/IP address pairings. It syslogs activity and reports certain changes via email.  Arpwatch uses pcap(3) to lis-
       ten for arp packets on a local ethernet/tokenring/fddi 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 MAC/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.

       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 MAC/IP address pair has been used for the first time six months or more.

       new station
	      The MAC address has not been seen before.

       flip flop
	      The MAC address has changed from the most recently seen address to the second most recently seen address.  (If either the old or new
	      MAC address is a DECnet address and it is less than 24 hours, the email version of the report is suppressed.)

       changed MAC address
	      The host switched to a new MAC address.

SYSLOG MESSAGES

       Here are some of the syslog messages; note that messages that are reported are also sysloged.

       MAC broadcast
	      The MAC 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.

       MAC broadcast
	      The source MAC address was all ones or all zeros.

       MAC mismatch
	      The source MAC address didn't match the address inside the arp packet.

       reused old MAC address
	      The MAC 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 - MAC/IP address database
       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.

4th Berkeley Distribution					  8 October 2000						       ARPWATCH(8)