Below shows the routing table and EIGRP topology table on RT1:
RT1#sh ip route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets D 172.16.1.0 [90/2172416] via 10.10.10.2, 00:00:14, Serial0/0 10.0.0.0/30 is subnetted, 3 subnets D 10.10.10.8 [90/2681856] via 10.10.10.2, 00:00:15, Serial0/0 [90/2681856] via 10.10.10.6, 00:00:15, Serial0/1 C 10.10.10.0 is directly connected, Serial0/0 C 10.10.10.4 is directly connected, Serial0/1 RT1# RT1#sh ip eigrp topo IP-EIGRP Topology Table for AS(100)/ID(10.10.10.5) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.10.10.8/30, 2 successors, FD is 2681856 via 10.10.10.6 (2681856/2169856), Serial0/1 via 10.10.10.2 (2681856/2169856), Serial0/0 P 10.10.10.0/30, 1 successors, FD is 2169856 via Connected, Serial0/0 P 10.10.10.4/30, 1 successors, FD is 2169856 via Connected, Serial0/1 P 172.16.1.0/24, 1 successors, FD is 2172416 via 10.10.10.2 (2172416/28160), Serial0/0 RT1#
RT1 has no feasible successor to 172.16.1.0/24. Hence it will query RT3 for a new successor when the link between RT1 and RT2 has failed.
Below simulates a network connectivity problem by applying an access list to prevent RT2 EIGRP Hello packets from reaching to RT1 S0/0.
RT1#conf t Enter configuration commands, one per line. End with CNTL/Z. RT1(config)#access-list 101 deny eigrp any host 224.0.0.10 RT1(config)#int s0/0 RT1(config-if)#ip access-group 101 in RT1(config-if)#^Z RT1# RT1#sh ip eigrp neighbors IP-EIGRP neighbors for process 100 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 1 10.10.10.6 Se0/1 13 00:02:06 1508 5000 0 4 0 10.10.10.2 Se0/0 5 00:02:20 400 2400 0 5 RT1#Note: The EIGRP default Hello and hold time intervals are 5 seconds and 15 seconds respectively.
Below shows the output messages of the debug ip eigrp, debug ip routing and debug eigrp fsm privileged command on RT1 for EIGRP convergence upon the connectivity problem. The EIGRP Query-Reply process occurred as there is no FS to the network.
RT1# 00:03:08: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (Serial0/0) is down: holding time expired 00:03:08: DUAL: linkdown: start - 10.10.10.2 via Serial0/0 00:03:08: DUAL: Destination 10.10.10.8/30 00:03:08: DUAL: Find FS for dest 10.10.10.8/30. FD is 2681856, RD is 2681856 00:03:08: DUAL: 10.10.10.6 metric 2681856/2169856 00:03:08: DUAL: 10.10.10.2 metric 4294967295/4294967295 found Dmin is 2681856 00:03:08: RT: delete route to 10.10.10.8 via 10.10.10.2, eigrp metric [90/2681856] 00:03:08: RT: NET-RED 10.10.10.8/30 00:03:08: DUAL: Removing dest 10.10.10.8/30, nexthop 10.10.10.2 00:03:08: DUAL: RT installed 10.10.10.8/30 via 10.10.10.6 00:03:08: DUAL: Send update about 10.10.10.8/30. Reason: lost if 00:03:08: DUAL: Destination 10.10.10.0/30 00:03:08: DUAL: Destination 10.10.10.4/30 00:03:08: DUAL: Destination 172.16.1.0/24 00:03:08: DUAL: Find FS for dest 172.16.1.0/24. FD is 2172416, RD is 2172416 00:03:08: DUAL: 10.10.10.2 metric 4294967295/4294967295 00:03:08: DUAL: 10.10.10.6 metric 2684416/2172416 not found Dmin is 2684416 00:03:08: DUAL: Peer total/stub 1/0 template/full-stub 1/0 00:03:08: DUAL: Dest 172.16.1.0/24 entering active state. 00:03:08: DUAL: Set reply-status table. Count is 1. 00:03:08: DUAL: Not doing split horizon 00:03:08: DUAL: linkdown: finish 00:03:08: IP-EIGRP(Default-IP-Routing-Table:100): 172.16.1.0/24 - do advertise out Serial0/1 00:03:08: IP-EIGRP(Default-IP-Routing-Table:100): Int 172.16.1.0/24 metric 4294967295 - 1657856 4294967295 00:03:08: IP-EIGRP(Default-IP-Routing-Table:100): Processing incoming REPLY packet 00:03:08: IP-EIGRP(Default-IP-Routing-Table:100): Int 172.16.1.0/24 M 2684416 - 1657856 1026560 SM 2172416 - 1657856 514560 00:03:08: DUAL: rcvreply: 172.16.1.0/24 via 10.10.10.6 metric 2684416/2172416 00:03:08: DUAL: reply count is 1 00:03:08: DUAL: Clearing handle 1, count now 0 00:03:08: DUAL: Freeing reply status table 00:03:08: DUAL: Find FS for dest 172.16.1.0/24. FD is 4294967295, RD is 4294967295 found 00:03:08: RT: delete route to 172.16.1.0 via 10.10.10.2, eigrp metric [90/2172416] 00:03:08: RT: no routes to 172.16.1.0 00:03:08: RT: NET-RED 172.16.1.0/24 00:03:08: RT: delete subnet route to 172.16.1.0/24 00:03:08: RT: NET-RED 172.16.1.0/24 00:03:08: RT: delete network route to 172.16.0.0 00:03:08: RT: NET-RED 172.16.0.0/16 00:03:08: DUAL: Removing dest 172.16.1.0/24, nexthop 10.10.10.2 00:03:08: RT: add 172.16.1.0/24 via 10.10.10.6, eigrp metric [90/2684416] 00:03:08: RT: NET-RED 172.16.1.0/24 00:03:08: DUAL: RT installed 172.16.1.0/24 via 10.10.10.6 00:03:08: DUAL: Send update about 172.16.1.0/24. Reason: metric chg 00:03:08: DUAL: Send update about 172.16.1.0/24. Reason: new if 00:03:08: IP-EIGRP(Default-IP-Routing-Table:100): Int 10.10.10.8/30 metric 2681856 - 1657856 1024000 00:03:08: IP-EIGRP(Default-IP-Routing-Table:100): Int 172.16.1.0/24 metric 2684416 - 1657856 1026560 RT1# RT1#sh ip eigrp topo IP-EIGRP Topology Table for AS(100)/ID(10.10.10.5) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.10.10.8/30, 1 successors, FD is 2681856 via 10.10.10.6 (2681856/2169856), Serial0/1 P 10.10.10.0/30, 1 successors, FD is 2169856 via Connected, Serial0/0 P 10.10.10.4/30, 1 successors, FD is 2169856 via Connected, Serial0/1 P 172.16.1.0/24, 1 successors, FD is 2684416 via 10.10.10.6 (2684416/2172416), Serial0/1 RT1# RT1#sh ip route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets D 172.16.1.0 [90/2684416] via 10.10.10.6, 00:00:15, Serial0/1 10.0.0.0/30 is subnetted, 3 subnets D 10.10.10.8 [90/2681856] via 10.10.10.6, 00:00:15, Serial0/1 C 10.10.10.0 is directly connected, Serial0/0 C 10.10.10.4 is directly connected, Serial0/1 RT1#
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