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EIGRP Redistribution Problem

I was reading a Cisco 360 article (BRKRST-3330) and spotted a cool problem I’ve not run into with regards to redistribution. In the topology below, R2 is learning the external EIGRP route 34.34.34.0/24, but R1 is not.

EIGRP - Redisribution Problem

R2#show ip route | b Gate
Gateway of last resort is not set

     34.0.0.0/24 is subnetted, 1 subnets
D EX    34.34.34.0 [170/256005120] via 23.23.23.3, 00:43:04, FastEthernet0/1
     23.0.0.0/24 is subnetted, 1 subnets
C       23.23.23.0 is directly connected, FastEthernet0/1
     12.0.0.0/24 is subnetted, 1 subnets
C       12.12.12.0 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, Loopback0

So R2 is learning the 34.34.34.0/24 network, but you can see below that R1 has no idea about it.

R1#show ip route | b Gate
Gateway of last resort is not set

     23.0.0.0/24 is subnetted, 1 subnets
D       23.23.23.0 [90/30720] via 12.12.12.2, 00:00:25, FastEthernet0/0
     12.0.0.0/24 is subnetted, 1 subnets
C       12.12.12.0 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, Loopback0

So we know that R2 is receiving the route which means the redistribution on R3 is working. We also know R1 is learning about the 23.23.23.0/24 network dynamically via EIGRP, which means the neighbor relationship is working. So why isn’t R1 receiving the route? My approach would be to check for any ACL’s or distribute lists that might be blocking the 34.34.34.0/24 network from being advertised between R2 and R1. However in this network, there are none. Actually the problem is the router-id. If we check which router advertised this network, we can see in the topology table on R2 that it was advertised from an originating router of 192.168.1.1 via 23.23.23.3¬†on interface fa0/1. See the output below.

R2#show ip eigrp topology 34.34.34.0 255.255.255.0
IP-EIGRP (AS 1): Topology entry for 34.34.34.0/24
  State is Passive, Query origin flag is 1, 1 Successor(s), FD is 256005120
  Routing Descriptor Blocks:
  23.23.23.3 (FastEthernet0/1), from 23.23.23.3, Send flag is 0x0
      Composite metric is (256005120/256002560), Route is External
      Vector metric:
        Minimum bandwidth is 10 Kbit
        Total delay is 200 microseconds
        Reliability is 10/255
        Load is 10/255
        Minimum MTU is 10
        Hop count is 1
      External data:
        Originating router is 192.168.1.1
        AS number of route is 1
        External protocol is OSPF, external metric is 0
        Administrator tag is 0 (0x00000000)

So lets confirm that the R3 neighbor has the originating router-id of this network (as this is where the topology table above says we learnt the route from).

R3#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(192.168.1.1)

So although it was R3 who originated this route in the EIGRP domain, when you check the router-id of R1, it is the same.

R1#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(192.168.1.1)
...
output omitted
!

It’s one of the few common problems in EIGRP, and it’s a pain in the arse to troubleshoot unless you have some good logging on your EIGRP neighbors. The following log helps troubleshoot this.

R1#sh run | s eigrp
router eigrp 1
 network 12.12.12.0 0.0.0.255
 no auto-summary
 eigrp event-logging
...
R1#sh log
*Mar  1 01:44:04.419: %DUAL-6-EVENT: IP-EIGRP(0), 21   Ignored route, dup router: 192.168.1.1
*Mar  1 01:44:04.419: %DUAL-6-EVENT: IP-EIGRP(0), 22   Ignored route, neighbor info: 12.12.12.2 FastEthernet0/1
*Mar  1 01:44:04.419: %DUAL-6-EVENT: IP-EIGRP(0), 23   Ignored route, metric: 34.34.34.0 256007680

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