NAME

ipguard - tool designed to protect Ethernet LAN IP address space by ARP spoofing.

SYNOPSIS

ipguard [-h] [-ajgrxziovd] [-f ethers] [-l log] [-p pid] [-m mac] [-c filter] [-u seconds] [-k seconds] [-n fakes] [-t mseconds] [-b buf] [-s user] <iface>

DESCRIPTION

ipguard listens network for ARP packets. All permitted MAC-IP pairs listed in 'ethers' file. If it receives one with MAC-IP pair, which is not listed in 'ethers' file, it will send ARP reply with configured fake address. This will prevent not permitted host to work properly in local ethernet segment.

OPTIONS

-f | -e ethers: Ethers file. Format of `ethers' file described in `ethers.sample' and ethers(5). Default `/etc/ethers'.
-l log: Log file. Default `/var/log/ipguard_<iface>.log'.
-p pid: Pid file. Default `/var/run/ipguard_<iface>.pid'.
-m mac: Fake MAC address. Will be sent in ARP reply as MAC of unlisted computer. Default `de:ad:xx:xx:xx:xx', `x' == random hex number.
-c filter: PCAP filter expression. Default no filter.
-u seconds: Update ethers interval. Time between checks `ethers' file for changes and rescan if any. Default 0 == no autoupdate.
-k seconds: Periodic regenerate fake MAC address. Default 0 == no regenerate.
-n fakes: Fake replies number. Default 2 replies.
-t mseconds: Time between fakes. Default 50 milliseconds.
-b buf: MAC buffer size. Number of last bad MAC-IP pairs stored in buffer. Default 0 == no buffer.
-s user: Drop root privileges to user. Default do not drop.
-a: No address substitution. Like 0.0.0.0 or 00:00:00:00:00:00.
-j: Disable first MAC-IP pair autodetect from interface.
-g: Default to grant. Do not block MAC or IP if both not in list.
-r: Read only. Do not send anything to net. Only listen.
-x: Duplex mode. Send fake packets not only to pirate but to request for pirate's address too.
-z: Send broadcast who-has to fix all client ARP tables broked by pirate.
-i: Hidden mode. Do not block gratuitous ARP packets.
-o: Promiscuous mode. Enable promiscuous mode. Usually useless.
-v: Verbose. Some more messages.
-d: Don't fork. Do not go to background and write all events to STDERR.
-dd: Debug
-ddd: Debug more
-h: Help. Short command line parameters description.

EXAMPLES

Normal recommended mode, duplex, broadcast fix, autoupdate /etc/ethers every 5 min:: ipguard -xz -u 300 fxp0
Same but with PCAP filter for only 192.168.1.0/24 network:: ipguard -xz -u 300 -c 'net 192.168.0.0/24' fxp0
Read-only mode and remember last 100 not listed in `ethers' MACs. Useful for initial MAC-IP pairs collection:: ipguard -r -b 100 -f /dev/null rl0
Run ipguard for a while then `killall -USR2 ipguard' and you'll get dump of 100 most recent MAC-IP pairs.
Do not go to background and be more verbose, with test ethers file:: ipguard -vd -f /tmp/ethers my1

TIPS

First MAC-IP pair in `ethers' always must be self MAC/IP addresses. Normally them automatically taken from listening interface. But if `-j' option specified then make sure that first pair is a source MAC/IP.

If you want to start more than one ipguard on segment for redundancy, you must specify same fake MAC address for every ipguard and find method to synchronize `ethers' files.

SIGNALS

SIGHUP: rescan `ethers' and reopen log file
SIGUSR1: dump some tables and statistics
SIGUSR2: dump new MAC-IP table in ethers(5) format

FILES

/etc/ethers: MAC-IP pairs list
/var/log/ipguard_<iface>.log: log file
/var/run/ipguard_<iface>.pid: pid file

BUGS

Do not use wildcard IP 0.0.0.0 in `ethers' with -x option. Legal clients will be banned. Discovered by irix.

Strange bug with libnet_get_hwaddr() isn't working on OpenBSD 4.0 discovered by irix. Use -j option.

ipguard will not prevent changing MAC address along with IP by pirate.

Signals HUP, USR1 or USR2 works only when received new ARP packet. It's not a bug, it's a feature.

When using -s <user> option ipguard will drop root privileges after creating log and pid files. So it will not delete or reopen these files.

Probably too many command line options. Another one or two and i'll put them all into /etc/ethers as comments.

ipguard was written as simple small tool and i haven't any plans for support of external databases SQL/LDAP/Whatever. Use scripts.

AUTHOR

SeaD <sead at deep.perm.ru>