As outlined earlier, in order to be able to route packets, routers require to have a routing table, this is the definitive list of networks that the router knows about. Its this routing table that routers solely use to make packet forwarding decisions.
A Routing Table contains the following information:
- The destination network and subnet mask
- The “next hop” router to get to the destination network
- Routing metrics and Administrative Distance
A Routing Table will contain information about two types of protocol;
A routed protocol is the protocol that is concerned with end to end connections, its a layer 3 protocol that applies logical addresses to devices and routes data between networks. Most common example would be IP
A routing protocol dynamically builds the network, topology, and next hop information in routing tables. Examples would be RIP, IGRP, OSPF, etc.
Remember the routing protocol does the routing on behalf of the routed protocol. It is important to understand the difference between the two
To determine the best route to a destination, a router considers various items, the most common will be the following;
• Metric (within a routing protocol)
• Administrative Distance (between separate routing protocols)