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how to set firewall for linux

how to set firewall for linux

To build a Linux IP firewall, it is necessary to have a kernel built with IP firewall support and the appropriate configuration utility.

In all production kernels prior to the 2.2 series, you would use the ipfwadm utility. The 2.2.x kernels marked the release of the third generation of IP firewall for Linux called IP Chains. . The netfilter code is the result of a large redesign of the packet handling flow in Linux. The netfilter is a multifaceted creature, providing direct backward-compatible support for both ipfwadm and ipchains as well as a new alternative command called iptables. We’ll talk about the differences between the three in the next few sections.

Kernel Configured with IP Firewall :

The Linux kernel must be configured to support IP firewalling. Configuring the Networking Hardware”. In 2.2 kernels you should select the following options:

Networking options —>
[*] Network firewalls
[*] TCP/IP networking
[*] IP: firewalling
[*] IP: firewall packet logging

In kernels 2.4.0 and later you should select this option instead:

Networking options —>
[*] Network packet filtering (replaces ipchains)
IP: Netfilter Configuration —>
Userspace queueing via NETLINK (EXPERIMENTAL)
IP tables support (required for filtering/masq/NAT)
limit match support
MAC address match support
netfilter MARK match support
Multiple port match support
TOS match support
Connection state match support
Unclean match support (EXPERIMENTAL)
Owner match support (EXPERIMENTAL)
Packet filtering
REJECT target support
MIRROR target support (EXPERIMENTAL)
Packet mangling
TOS target support
MARK target support
LOG target support
ipchains (2.2-style) support
ipfwadm (2.0-style) suppo


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