EIGRP automatically selects an IP address as the Router ID when an EIGRP process is started. EIGRP does not use Router ID as extensively as OSPF. The only time EIGRP uses the Router ID is when redistributing external routes into an EIGRP routing domain. The Originating Router field of an EIGRP IP External Route packet indicates the Router ID of the redistributing router.
The EIGRP Router ID is selected in the same manner as OSPF Router ID – the highest local IP address is selected and loopback interfaces are preferred. The Router ID is not changed unless the EIGRP process is totally restarted with the no router eigrp command or when the Router ID is manually configured and changed with the eigrp router-id {router-id} router subcommand.
Below shows the routing tables on RT1 and RT2 before redistributing the static route to 100.100.100.0/24 into EIGRP on RT2:
RT1#sh ip route Gateway of last resort is not set 10.0.0.0/30 is subnetted, 1 subnets C 10.10.10.0 is directly connected, Serial0/0 C 192.168.1.0/24 is directly connected, FastEthernet1/0 RT1# RT1#clear ip eigrp events RT1#sh ip eigrp events Event information for AS 100: Event log is empty. RT1# ---------------------------------------------------------------------- RT2#sh ip route Gateway of last resort is not set 100.0.0.0/24 is subnetted, 1 subnets S 100.100.100.0 [1/0] via 23.23.23.3 23.0.0.0/24 is subnetted, 1 subnets C 23.23.23.0 is directly connected, FastEthernet1/0 10.0.0.0/30 is subnetted, 1 subnets C 10.10.10.0 is directly connected, Serial0/0 192.168.1.0/32 is subnetted, 1 subnets C 192.168.1.1 is directly connected, Loopback0 RT2#
Below shows configuration steps on RT2 to redistribute the static route into EIGRP:
RT2#conf t Enter configuration commands, one per line. End with CNTL/Z. RT2(config)#router eigrp 100 RT2(config-router)#redistribute static ? metric Metric for redistributed routes route-map Route map reference <cr> RT2(config-router)#redistribute static RT2(config-router)#^Z RT2# RT2#sh ip eigrp topology IP-EIGRP Topology Table for AS(100)/ID(192.168.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.10.10.0/30, 1 successors, FD is 2169856 via Connected, Serial0/0 P 100.100.100.0/24, 1 successors, FD is 28160 via Rstatic (28160/0) RT2# RT2#sh ip eigrp topology 100.100.100.0 % IP-EIGRP (AS 100): Route not in topology table RT2#sh ip eigrp topology 100.100.100.0 255.255.255.0 IP-EIGRP (AS 100): Topology entry for 100.100.100.0/24 State is Passive, Query origin flag is 1, 1 Successor(s), FD is 28160 Routing Descriptor Blocks: 23.23.23.3, from Rstatic, Send flag is 0x0 Composite metric is (28160/0), Route is External Vector metric: Minimum bandwidth is 100000 Kbit Total delay is 100 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 0 External data: Originating router is 192.168.1.1 (this system) AS number of route is 0 External protocol is Static, external metric is 0 Administrator tag is 0 (0x00000000) RT2#
Below shows that RT1 discards the external route originated from RT2 as it found out that the Originating Router field of the external route is same as its Router ID. RT1 does not insert the route into its EIGRP topology table (and routing table) to prevent a routing loop – it thinks that it is the originator of the route; by receiving the route back from other neighbors, it must be a loop.
RT1#sh ip route Gateway of last resort is not set 10.0.0.0/30 is subnetted, 1 subnets C 10.10.10.0 is directly connected, Serial0/0 C 192.168.1.0/24 is directly connected, FastEthernet1/0 RT1# RT1#sh ip eigrp events Event information for AS 100: 1 00:02:29.967 Ignored route, metric: 100.100.100.0 2172416 2 00:02:29.967 Ignored route, neighbor info: 10.10.10.2 Serial0/1 3 00:02:29.967 Ignored route, dup router: 192.168.1.1 RT1# RT1#sh ip eigrp topology IP-EIGRP Topology Table for AS(100)/ID(192.168.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.10.10.0/30, 1 successors, FD is 2169856 via Connected, Serial0/0 RT1#
Below shows a possible solution of the problem – modify the EIGRP Router ID of RT1. Changing the subnet between RT1 and RT2 from 10.10.10.0/30 to 200.200.200.0/30 is another feasible solution the Router ID of RT1 will be changed from 192.168.1.1 to 200.200.200.1.
RT1#conf t Enter configuration commands, one per line. End with CNTL/Z. RT1(config)#router eigrp 100 RT1(config-router)#eigrp router-id 1.1.1.1 RT1(config-router)#^Z RT1# 00:04:25: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (Serial0/0) is down: route configuration changed 00:04:28: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.2 (Serial0/0) is up: new adjacency RT1#sh ip route Gateway of last resort is not set 100.0.0.0/24 is subnetted, 1 subnets D EX 100.100.100.0 [170/2172416] via 10.10.10.2, 00:00:08, Serial0/0 10.0.0.0/30 is subnetted, 1 subnets C 10.10.10.0 is directly connected, Serial0/0 C 192.168.1.0/24 is directly connected, FastEthernet1/0 RT1# RT1#sh ip eigrp topology IP-EIGRP Topology Table for AS(100)/ID(1.1.1.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.10.10.0/30, 1 successors, FD is 2169856 via Connected, Serial0/0 P 100.100.100.0/24, 1 successors, FD is 2172416 via 10.10.10.2 (2172416/28160), Serial0/0 RT1# ---------------------------------------------------------------------- RT2# 00:04:22: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.1 (Serial0/0) is down: Interface Goodbye received 00:04:27: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 100: Neighbor 10.10.10.1 (Serial0/0) is up: new adjacency RT2#
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