ipchains was ipfwadm's successor. It too is an IP accounting and packet filtering administration service but was mainly used with Linux Kernel 2.2.x versions. ipchains is still used today and is also available to use with Linux Kernel 2.4.x.

Here is an example of ipchains:

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ipchains -F input
ipchains -P input REJECT

# local interface, local machines, going anywhere is valid
#
ipchains -A input -i $intint -s $intnet -d 0.0.0.0/0 -j ACCEPT

# remote interface, claiming to be local machines, IP spoofing, get lost
#
ipchains -A input -i $extint -s $intnet -d 0.0.0.0/0 -l -j REJECT

# remote interface, any source, going to permanent PPP address is valid
#
ipchains -A input -i $extint -s 0.0.0.0/0 -d $extip/32 -j ACCEPT

# loopback interface is valid.
#
ipchains -A input -i lo -s 0.0.0.0/0 -d 0.0.0.0/0 -j ACCEPT

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More information on ipchains can be found here.

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by howe81