Last Updated on August 7, 2021 by Admin 3
You administer a router that contains five routes to the same network: an eBGP route, an ISIS route, a RIP route, an OSPF route, and an internal EIGRP route. The default ADs are used.
Which route does the router prefer? (Select the best answer.)
- the eBGP route
- the ISIS route
- the RIP route
- the OSPF route
- the EIGRP route
The router prefers the external Border Gateway Protocol (eBGP) route. When multiple routes to a network exist and each route uses a different routing protocol, a router prefers the routing protocol with the lowest administrative distance (AD). The following list contains the most commonly used ADs:
If the eBGP route were to fail, the internal Enhanced Interior Gateway Routing Protocol (EIGRP) route would be preferred, because EIGRP has an AD of 90. If the EIGRP route were also to fail, the Open Shortest Path First (OSPF) route would be preferred, because OSPF has an AD of 110. If the OSPF route were also to fail, the Intermediate SystemtoIntermediate System (ISIS) route would be preferred, because ISIS has an AD of 115. The Routing Information Protocol (RIP) route would not be used unless all of the other links were to fail, because RIP has an AD of 120.
ADs for a routing protocol can be manually configured by issuing the distance command in router configuration mode. For example, to change the AD of RIP from 120 to 80, you should issue the following commands:
RouterA(config)#router rip RouterA(configrouter)#distance 80
If you were to modify the AD of RIP by issuing the distance command, the RIP route would be preferred before the EIGRP route but after the eBGP route.
You can view the AD of the best route to a network by issuing the show ip routecommand. The AD is the first number inside the brackets in the output. For example, the following router output shows an OSPF route with an AD of 160:
Router#show ip route Gateway of last resort is 10.19.54.20 to network 10.140.0.0 O E2 18.104.22.168 [160/5] via 10.19.54.6, 0:01:00, Ethernet2