EIGRP with the same Router ID – part 2

This is the continuation from part 1. We are still going to be using the same topology – see Figure 1. We are going to lab scenario two where R1 and R3 will have both the same eigrp router ID.

eigrp-rid-topo

Figure 1

I have removed the router-id 1.1.1.1 on R2 using the command no eigrp router-id 1.1.1.1. R3 has full neighbor relationship with R2 and R3 is receiving routes from R2. After fixing the router ID of R2. R2 is now accepting routes from R1 and R2 is advertising the routes to R3. Example 1 shows R3 route table.

Example 1

R3#show ip route
...
      10.0.0.0/8 is variably subnetted, 11 subnets, 2 masks
D       10.0.1.0/24 [90/435200] via 10.0.23.2, 00:00:14, Ethernet1/1
D       10.0.2.0/24 [90/409600] via 10.0.23.2, 00:00:14, Ethernet1/1
C       10.0.3.0/24 is directly connected, Loopback0
L       10.0.3.1/32 is directly connected, Loopback0
D EX    10.0.10.0/24 [170/309760] via 10.0.23.2, 00:00:14, Ethernet1/1
D       10.0.12.0/24 [90/307200] via 10.0.23.2, 00:00:14, Ethernet1/1
D       10.0.20.0/24 [90/409600] via 10.0.23.2, 00:00:14, Ethernet1/1
C       10.0.23.0/24 is directly connected, Ethernet1/1
L       10.0.23.3/32 is directly connected, Ethernet1/1
C       10.0.30.0/24 is directly connected, Loopback1
L       10.0.30.1/32 is directly connected, Loopback1
R3#

As you can see, R3 is receiving the routes 10.0.1.0/24 and 10.0.10.0/24 from R1. R1 is also receiving R3 routes as shown in Example 2.

Example 2

R1#show ip route
...
     10.0.0.0/8 is variably subnetted, 11 subnets, 2 masks
C      10.0.1.0/24 is directly connected, Loopback0
L      10.0.1.1/32 is directly connected, Loopback0
D      10.0.2.0/24 [90/409600] via 10.0.12.2, 00:01:11, Ethernet1/0
D      10.0.3.0/24 [90/435200] via 10.0.12.2, 00:01:11, Ethernet1/0
C      10.0.10.0/24 is directly connected, Loopback1
L      10.0.10.1/32 is directly connected, Loopback1
C      10.0.12.0/24 is directly connected, Ethernet1/0
L      10.0.12.1/32 is directly connected, Ethernet1/0
D      10.0.20.0/24 [90/409600] via 10.0.12.2, 00:01:11, Ethernet1/0
D      10.0.23.0/24 [90/307200] via 10.0.12.2, 00:01:11, Ethernet1/0
D      10.0.30.0/24 [90/435200] via 10.0.12.2, 00:01:11, Ethernet1/0
R1#

I am going to change the router ID of R3 to 1.1.1.1, and let’s see what’s going to happen. In Example 3

Example 3

R3#show run | sec router
router eigrp 1
 network 0.0.0.0
 eigrp router-id 1.1.1.1
R3#

In Example 4, R2 shows that it is still has a neighbor relationship to both R1 and R2 despite that both routers have the same RID.

Example 4

R2#show ip eigrp neighbors 
EIGRP-IPv4 Neighbors for AS(1)
H   Address             Interface       Hold Uptime     SRTT    RTO  Q   Seq
                                        (sec)           (ms)         Cnt Num
1   10.0.23.3           Et1/1             14 00:00:57     16    100   0   17
0   10.0.12.1           Et1/0             11 00:06:45     12    100   0   13
R2#

Example 5 shows R1, R2 and R3 route tables. As you noticed, R1 lost all the routes (10.0.3.0/24 and 10.0.30.0/24) from R3 and R3 lost R1’s routes (10.0.1.0.24 and 10.0.10.0/24). However, R2 is still has the all the routes.

Example 5

R1#show ip route eigrp 
...
     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
D      10.0.2.0/24 [90/409600] via 10.0.12.2, 00:19:15, Ethernet1/0
D      10.0.20.0/24 [90/409600] via 10.0.12.2, 00:19:15, Ethernet1/0
D      10.0.23.0/24 [90/307200] via 10.0.12.2, 00:19:15, Ethernet1/0
R1#

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

R2#show ip route eigrp 
...
     10.0.0.0/8 is variably subnetted, 12 subnets, 2 masks
D      10.0.1.0/24 [90/409600] via 10.0.12.1, 00:19:39, Ethernet1/0
D      10.0.3.0/24 [90/409600] via 10.0.23.3, 00:13:52, Ethernet1/1
D EX   10.0.10.0/24 [170/284160] via 10.0.12.1, 00:19:39, Ethernet1/0
D      10.0.30.0/24 [90/409600] via 10.0.23.3, 00:13:52, Ethernet1/1
R2#

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

R3#show ip route eigrp 
...
     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
D      10.0.2.0/24 [90/409600] via 10.0.23.2, 00:13:38, Ethernet1/1
D      10.0.12.0/24 [90/307200] via 10.0.23.2, 00:13:38, Ethernet1/1
D      10.0.20.0/24 [90/409600] via 10.0.23.2, 00:13:38, Ethernet1/1
R3#

Even though there is a router in the middle of R1 and R3, eigrp behaves the same way as it was in part 1. When the router sees its router ID in an update, it will not accept the update because it thinks that there is a loop in the network.

I removed the router ID 1.1.1.1 on R3, and put the router ID 1.1.1.1 back on R2. By doing this R1 lost R2 routes, but kept R3 routes. See Example 6 for R1, R2 and R3 route tables.

Example 6

R1#show ip route eigrp 
...
     10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
D      10.0.3.0/24 [90/435200] via 10.0.12.2, 00:07:07, Ethernet1/0
D      10.0.30.0/24 [90/435200] via 10.0.12.2, 00:07:07, Ethernet1/0
R1#

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

R2#show ip route eigrp 
...
     10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
D      10.0.3.0/24 [90/409600] via 10.0.23.3, 00:07:40, Ethernet1/1
D      10.0.30.0/24 [90/409600] via 10.0.23.3, 00:07:40, Ethernet1/1
R2#

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
[
R3#show ip route eigrp 
...
     10.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
D     10.0.2.0/24 [90/409600] via 10.0.23.2, 00:08:07, Ethernet1/1
D     10.0.12.0/24 [90/307200] via 10.0.23.2, 00:08:07, Ethernet1/1
D     10.0.20.0/24 [90/409600] via 10.0.23.2, 00:08:07, Ethernet1/1
R3#

R1 accepted the routes (10.0.3.0/24 and 10.0.30.0/24) from R3 which is being advertised my R2 to R1. The reason R1 accepted this routes is because the updates generated by R3 does not have 1.1.1.1 RID in it; therefore, R1 accepted the routes from R3, but ignores the route update from R2 because of duplicated RID.

R3 does not have R1 routes because R2 thinks R1 updates would cause a routing loop. Therefore, R2 will not install R1 updates to its route table and it will not pass it along to R3.

There you have it.

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About networkshinobi

This blog is about the things I learned about computers and networking to help me to remember them as I push further my studies. I created this blog to help myself to continue my education; and if you find this blog helpful for your studies, that is great. That is one of the reasons why I made this blog, to share my interest and knowledge. Also, all the entries/posts I made are based on my views, opinion and for educational purposes only. If you see some mistakes, feel free to drop some comments. I would appreciate all the helpful comments. Thanks
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