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Routing tables are also a key aspect of certain security operations, such as unicast reverse path forwarding (uRPF). [2] In this technique, which has several variants, the router also looks up, in the routing table, the source address of the packet.
A forwarding information base (FIB), also known as a forwarding table or MAC table, is most commonly used in network bridging, routing, and similar functions to find the proper output network interface controller to which the input interface should forward a packet. It is a dynamic table that maps MAC addresses to ports. It is the essential ...
IP forwarding algorithms in most routing software determine a route through a shortest path algorithm. In routers, packets arriving at an interface are examined for source and destination addressing and queued to the appropriate outgoing interface according to their destination address and a set of rules and performance metrics.
Before or after examining the destination, other tables may be consulted to make decisions to drop the packet based on other characteristics, such as the source address, the IP protocol identifier field, or Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) port number. Forwarding plane functions run in the forwarding element. [1]
The routing process usually directs forwarding on the basis of routing tables. Routing tables maintain a record of the routes to various network destinations. Routing tables may be specified by an administrator, learned by observing network traffic or built with the assistance of routing protocols. Routing, in a narrower sense of the term ...
When a router receives a packet, it searches its routing table to find the best match between the destination IP address of the packet and one of the addresses in the routing table. Once a match is found, the packet is encapsulated in the layer-2 data link frame for the outgoing interface indicated in the table entry.
In standard unicast IP routing, the router forwards the packet away from the source to make progress along the distribution tree and prevent routing loops. In contrast, the router's multicast forwarding state runs more logically by organizing tables based on the reverse path, from the receiver back to the root of the distribution tree at the ...
Since a forwarding decision must be made for every packet handled by a node, the total time required for this can become a major limiting factor in overall network performance. Much of the design effort of high-speed routers and switches has been focused on making rapid forwarding decisions for large numbers of packets.