Routing Tables
A routing table is a database repository that holds the router's routing information that represents each possible logical destination network that is known to the router. The entries for major networks are listed in ascending order and, most commonly, within each major network the subnetworks are listed in descending order. If the routing table entry points to an IP address, the router will perform a recursive lookup on that next-hop address until the router finds an interface to use. The router will switch the packet to the outbound interfaces buffer. The router will then determine the Layer 2 address that maps to the Layer 3 address. The packet will then be encapsulated in a Layer 2 frame appropriate for the type of encapsulation used by the outbound interface. The outbound interface will then place the packet on the medium and forward it to the next hop. The packet will continue this process until it reaches its destination.
There are two ways in which a routing table can be populated: a route can be entered manually, this is called static routing, or a router can dynamically learning a route. Once a router learns a route, it is added to its route table.