Last Updated on August 6, 2021 by Admin 3
You administer the network in the following exhibit:
You issue the show runningconfig command on RouterA and receive the following partial output:
ip address 10.10.1.1 255.255.255.0
ip address 192.168.50.5 255.255.255.0
tunnel source Loopback0
tunnel destination 10.10.3.1
RouterA and RouterC are both configured to use RouterB as a gateway of last resort. Additionally, static routes to the Loopback0 interfaces on RouterA and RouterC have beenconfigured on RouterB.
You configure EIGRP on RouterA and then issue the show ip route command, which produces the following partial output:
Gateway of last resort is 18.104.22.168 to network 0.0.0.0
22.214.171.124/24 is subnetted, 1 subnets
C 126.96.36.199 is directly connected, Serial0/0
10.0.0.0/24 is subnetted, 2 subnets
10.10.1.0 is directly connected, Loopback0
10.10.3.0 [90/297372416] via 192.168.50.6, 00:00:01, Tunnel0
C 192.168.50.0/24 is directly connected, Tunnel0
S* 0.0.0.0/0 [1/0] via 188.8.131.52
Which of the following is true? (Select the best answer.)
- The Tunnel0 interface and EIGRP adjacency on RouterA will flap.
- The Tunnel0 interface and EIGRP adjacency on RouterA will function properly.
- The Tunnel0 interface on RouterA will function properly, but EIGRP will flap.
- The Tunnel0 interface on RouterA will flap, but the EIGRP adjacency will function properly.
The Tunnel0 interface and Enhanced Interior Gateway Routing Protocol (EIGRP) adjacency on RouterA will flap because the preferred route to the Tunnel0 destination interface is through the tunnel itself, which results in recursive routing. When recursive routing occurs, the Tunnel0 interfaces on both RouterA and RouterC will be temporarily disabled, which breaks the EIGRP adjacency.
The EIGRP adjacency will reestablish when the tunnel interfaces return to the up state. Therefore, if you were to issue the show ip route command on RouterA while the adjacency is established, you would see that the preferred route to the Loopback0 interface on RouterC from RouterA is through Tunnel0, even though the destination interface for Tunnel0 on RouterA is the Loopback0 interface on RouterC.
If the cause of the recursive routing is not fixed, the Tunnel0 interfaces will flap and errorssimilar to the following will be displayed on RouterA:
*Mar 1 00:26:15.379: %TUN5RECURDOWN: Tunnel0 temporarily disabled due to recursive routing
*Mar 1 00:26:16.379: %LINEPROTO5UPDOWN: Line protocol on Interface Tunnel0, changed state to down
*Mar 1 00:26:16.487: %DUAL5NBRCHANGE: IPEIGRP(0) 6: Neighbor 192.168.50.6 (Tunnel0) is down: interface down
In this scenario, an EIGRP adjacency has been established between the Tunnel0 interfaceson RouterA and RouterC. When the EIGRP adjacency comes up, the show ip route command displays Tunnel0 as the preferred route to 192.168.50.0 instead of the gateway of last resort. Therefore, the EIGRP 6 domain has been configured to include the 10.10.1.0/24 and 192.168.50.0/24 networks on RouterA and the 10.10.3.0/24 and 192.168.50.0/24 networks on RouterC. As a result, recursive routing to the 10.10.3.0 network through Tunnel0 occurs on RouterA and recursive routing to the 10.10.1.0 network occurs on RouterC.
There are two ways to resolve the recursive routing issue on both RouterA and RouterC in this scenario: remove the 192.168.50.0/24 network from the EIGRP 6 domain, or add a static route to the Tunnel0 destination IP addresses on both RouterA and RouterC. A static route has a lower administrative distance (AD) than EIGRP. Therefore, a static route would fix the recursive routing problem.