Ubuntu Manpage: arpwatch - keep track of ethernet/ip address pairings

Provided by: arpwatch_2.1a15-8.1build2_amd64

NAME

       arpwatch - keep track of ethernet/ip address pairings

SYNOPSIS

       arpwatch [ -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
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 -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 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 only logs bogons but otherwise ignores them. If this option is
specified, arpwatch will perform normal processing 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 supported. 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 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
       IFNAME.dat - ethernet/ip address database observed on interface IFNAME
       ethercodes.db - vendor ethernet block list

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.