routingtabell

A routingtabell, commonly known as a routing table, is a data structure inside a router or networked host that stores the routes used to determine where to forward packets. The table consists of entries that map destination prefixes to next-hop addresses or exit interfaces. Each entry typically includes the destination prefix (network address and prefix length), a next hop or interface, a metric, and a source indicating how the route was learned (static, dynamic protocol, connected, or local).

Routing tables are populated through static configuration or dynamic routing protocols such as OSPF, IS-IS, RIP, and BGP. They may also include local or connected routes for networks directly attached to the device. The forwarding decision is based on the longest prefix match; if multiple routes match, the route with the lowest administrative distance (trust level) is preferred, and if needed the lower metric is chosen.

Both IPv4 and IPv6 are supported, with entries expressed as appropriate prefixes. Dynamic protocols continuously exchange information to reflect topology changes, enabling the table to converge toward a stable set of paths. Routes can be summarized or redistributed between protocols, and entries may age out or be refreshed to reflect reachability.

In operation, the routing table guides the forwarding plane: for each incoming packet, the most specific matching entry determines the next hop or output interface. If no match exists, a default route may be used or the packet may be dropped. The routing table is therefore central to the efficiency and correctness of network traffic forwarding.