Packet manipulation involves intentionally modifying the IP packet header before it enters the path, commonly done by network administrators through NAT processes. The mangle table contains five chains, and Netfilter is a popular open source tool used for firewall and packet filtering rule set configuration. Packet manipulation is used to control data flow within a private network and manage packet header information for data packets sent over the Internet.
Package manipulation is best described as the intentional modification of
the information in the Internet Protocol (IP) packet header before it
enter the path. This intentional change is harmless, but it is a commonly used process by network administrators.
When data is transmitted from one computer to another via the
Internet, information is sent in a data packet. The packet header
contains sender and recipient information. It also contains information about the data actually transmitted, called payloads.
Packet manipulation is done via network address translation (NAT)
processes. This process is used as the packet moves through the
traffic routers. Within the NAT, you can set up translation tables
to edit the source IP address and destination IP address fields
automatically. This process is also called IP or network masquerading
masquerading, and is one of the most commonly used functions of packet mangling.
The main table used in this process is called the mangle table. The
the mangle table contains five chains: pre-routing, input, forward, output
and post-route. The packet enters the router and is checked
against the pre-milling chain of the cutting table. From there, it’s pushed
through the pre-routing chain of the network address translation table. At this point, it is determined if the package is for you. If it is, the packet is routed to the mangle table and is processed through the input, forward, and output routing processes, which ensures that the packet arrives at the addressed destination.
There are various methods for changing NAT settings and creating packet manipulation tables. Netfilter is one such tool. This software is a popular open source application used with Linux 2.4x to 2.6x for firewall. Netfilter itself modifies kernel modules to include callback functions for packets traveling up the network stack. Within Netfilter, iptables was created to allow system administrators to configure effective changes to the Linux 2.4x and 2.6x packet filtering rule set.
Packet manipulation is a core function of the NAT process and is used to control the flow of data packets within a private network. It is also used to manage packet header information for data packets sent over the Internet.
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