Ipchains
It is software which is based on Linux firewall which was rewritten after Linux’s IPv4 firewalling code, ipfwadm. In Linux 2.2, ipchains is necessary to administer the IP packet filters they were basically written because the previous IPv4 firewall code was used in Linux 2.0 which didn’t work with IP fragments and specification of protocols apart from TCP, UDP, and ICMP and is superseded by Linux 2.4.
