ARPWATCH(8)ARPWATCH(8)NAMEarpwatch - keep track of ethernet/ip address pairings
SYNOPSISarpwatch [ -dN ]
[ -f datafile ]
[ -i interface ]
[ -n net[/width ]]
[ -r file ]
[ -F filter ]
[ -s sendmail_path ]
[ -p ]
[ -a ]
[ -m addr ]
[ -u username ]
[ -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 net‐
mask 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 tcp‐
dump(1) or pcapture(1)) to read from instead of reading from the net‐
work. In this case, arpwatch does not fork.
(Debian) The -F option is used to specify a pcap filter, which provides
a generic way of ignoring specific packets. The applied pcap filter
will be "(arp or rarp) and not vlan and (filter)". See pcap-filter(7)
for the syntax of that string.
(Debian) The -s flag is used to specify the path to the sendmail pro‐
gram. 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 only logs bogons but otherwise ignores
them. If this option is specified, arpwatch will perform normal pro‐
cessing with bogon packets and send reports about detected events. This
option can be combined with -N to disable the report of the packet
being a bogon (processing will still be done).
(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 -Q flags prevents arpwatch from sending reports by mail.
(Debian) The -z option is used to set a range of ip addresses to ignore
(such as a DHCP range). Both the ignorenet and the ignoremask are
specified in numbers-and-dots notation and separated from each other by
a slash (/). Specifying the ignoremask by subnet length is not sup‐
ported. If the ignoremask is omitted, 255.255.255.255 is assumed.
Example: -z 192.168.10.0/255.255.255.0
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 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
/var/lib/arpwatch - default directory
IFNAME.dat - ethernet/ip address database observed on interface IFNAME
ethercodes.db - 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)
