Dynamic Routing & Administrative Distance (AD)

Dynamic Routing is again subdivided into two types:

a)      IGP – it will exchange private network information within the AS

b)      EGP – it will exchange public network information within the AS

Exterior Gateway Protocol (EGP)                       Interior Gateway Routing Protocol (IGP)

* BGP (Border Gateway Protocol)                             * RIP (Routing Information Protocol)

* EIGRP (Enhanced Interior Gateway Routing Protocol)

* OSPF (Open Shortest Path First)

                       

Administrative Distance (AD Values):

Depends on the AD value router will prefer the Routes (Thrust worthiness)

Select the best path:

Administrative distance is the first criterion that a router uses to determine which routing protocol to use if two protocols provide route information for the same destination. Administrative distance is a measure of the trustworthiness of the source of the routing information. Administrative distance has only local significance, and is not advertised in routing updates.

Note: The smaller the administrative distance value, the more reliable the protocol. For example, if a router receives a route to a certain network from both Open Shortest Path First (OSPF) (default administrative distance - 110) and Interior Gateway Routing Protocol (IGRP) (default administrative distance - 100), the router chooses IGRP because IGRP is more reliable. This means the router adds the IGRP version of the route to the routing table.