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

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.