Troubleshooting AD Redistribution

When it comes to redistribution, there are a lot of things that potentially could go wrong. Two possible issues are sub-optimal routing and routing loops. All redistribution problems boil down to two different issues:

• Metric related problems.
• Administrative distance related problems.

If you haven’t seen my first lesson on metric related redistribution problems then I would recommend to start there first. Once you know how to fix metric issues, this lesson will be easier to understand.

In this lesson we will take a look at redistribution problems that are caused by the administrative distance. I’ll also show you why this occurs and of course how to fix it!

This is the topology I will use:

Above we have 4 routers, let me explain this topology:

• R1 runs RIP and is only used to inject a prefix into the topology (1.1.1.0 /24).
• R2 runs RIP, OSPF and EIGRP. We will perform redistribution on this router in a bit.
• R3 runs OSPF and EIGRP, it will also be configured for redistribution.
• R4 runs only EIGRP.

Here’s what the configuration of the routing protocols look like:

R1#show running-config | section rip
router rip
 version 2
 network 1.0.0.0
 network 192.168.12.0
 no auto-summary

R2#show running-config | section rip
router rip
 version 2
 network 192.168.12.0
 no auto-summary

R2#show running-config | section ospf
router ospf 1
 log-adjacency-changes
 network 192.168.23.0 0.0.0.255 area 0

R2#show running-config | section eigrp
router eigrp 1
 network 192.168.24.0
 no auto-summary

R3#show running-config | section ospf
router ospf 1
 log-adjacency-changes
 network 192.168.23.0 0.0.0.255 area 0

R3#show running-config | section eigrp
router eigrp 1
 network 192.168.34.0
 no auto-summary

R4#show running-config | section eigrp
router eigrp 1
 network 192.168.24.0
 network 192.168.34.0
 no auto-summary

And here’s what the routing tables look like, we haven’t configured redistribution yet:

R2#show ip route

C    192.168.12.0/24 is directly connected, FastEthernet1/0
     1.0.0.0/24 is subnetted, 1 subnets
R       1.1.1.0 [120/1] via 192.168.12.1, 00:00:28, FastEthernet1/0
C    192.168.24.0/24 is directly connected, FastEthernet0/1
C    192.168.23.0/24 is directly connected, FastEthernet0/0
D    192.168.34.0/24 [90/307200] via 192.168.24.4, 00:00:33, FastEthernet0/1

R2 learns a prefix from R1 through RIP and it learns about the network in between R3 and R4 (192.168.34.0 /24). Let’s take a look at R3:

R3#show ip route

D    192.168.24.0/24 [90/307200] via 192.168.34.4, 00:01:23, FastEthernet0/1
C    192.168.23.0/24 is directly connected, FastEthernet0/0
C    192.168.34.0/24 is directly connected, FastEthernet0/1

R3 learns about the network (192.168.24.0 /24) in between R2 and R4 through EIGRP. Let’s check R4:

R4#show ip route

C    192.168.24.0/24 is directly connected, FastEthernet0/0
C    192.168.34.0/24 is directly connected, FastEthernet0/1

R4 didn’t learn anything so far. It’s an internal EIGRP router and the only two interfaces that are advertised in EIGRP are directly connected for R4.

hostname R1
!
interface Loopback0
 ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0
 ip address 192.168.12.1 255.255.255.0
!
router rip
 no auto-summary
 network 192.168.12.0
 network 1.1.1.0
!
end

hostname R2
!
interface FastEthernet0/0
 ip address 192.168.23.2 255.255.255.0
!
interface FastEthernet0/1
 ip address 192.168.24.2 255.255.255.0
!
interface FastEthernet1/0
 ip address 192.168.12.2 255.255.255.0
!
router rip
 no auto-summary
 network 192.168.12.0
!
router eigrp 1
 network 192.168.34.0
 network 192.168.24.0
!
router ospf 1
 network 192.168.23.0 0.0.0.255 area 0
!
end

hostname R3
!
interface FastEthernet0/0
 ip address 192.168.23.3 255.255.255.0
!
interface FastEthernet0/1
 ip address 192.168.34.3 255.255.255.0
!
router eigrp 1
 network 192.168.34.0
!
router ospf 1
 network 192.168.23.0 0.0.0.255 area 0
!
end

hostname R4
!
interface FastEthernet0/0
 ip address 192.168.24.4 255.255.255.0
!
interface FastEthernet0/1
 ip address 192.168.34.4 255.255.255.0
!
router eigrp 1
 no auto-summary
 network 192.168.34.0
 network 192.168.24.0
!
end

Redistribution Configuration

To achieve full connectivity, we have to configure redistribution. However, let’s say that we have some requirements…something you could encounter on a CCIE R&S lab exam:

• Configure redistribution between RIP and EIGRP on R2 only.
• Configure redistribution between OSPF and EIGRP on R3 only.