EIGRP and static route loop prevention

[AndreaC]

Good evening,
I am studying the Cisco CCNP ENARSI and I created this laboratory, applying different EIGRP features on various routers.
All the loopback IPs, both IPv4 and IPv6, ping each other correctly, both on the primary routes (EIGRP 10 and EIGRP 40) and on the secondary routes (EIGRP 30 and default static route).
On R1 and R3 I created 2 route-maps to prevent any loops (I'm not 100% sure if it works):
- set tag 10 for redistribution eigrp 30 to eigrp 10
- deny tag 10 and generic permit for redistribution of eigrp 10 to eigrp 30
I would like to create a rule to prevent any loops between R2, R3 and R5, but I don't know how to do it. Could you give me some help?
On R2, between eigrp 10 and eigrp 40, I think I'm taking inspiration from the 2 route maps created on R1 and R3, the "problem" is that I don't know how to create a block on R3 and R5.
Maybe in a scenario like this, it is not possible to prevent loops between R2, R3 and R5?
Thanks to anyone who can help me.
In the attachment you can find the configurations of R1, R2, R3 and R5.

 

 

[David Ruess]

Hello,

This is a very complex topology especially for ENARSI. You may want to create smaller more manageable labs to understand the concepts. I say that because you mention that you arent "100% sure if it works" for some of your configuration which is not ideal for us to help you with a completely different problem.

Secondly EIGRP will not cause loops inherently. Follow this logic:

If R2 learns an EIGRP route form R4 it will install that in its routing table. Then you redistribute that into your network and R2 sends it out. Even throughout the network it gets redistributed by all routers along the path in our network, even if it got back to R2 it wuld have a higher metric and R2 would not use it for forwarding. 

Something you "could" try that may work is on each router redistribute connected and add a tag identifying the routers #. For instance all R2s routes will have a tag of 2.

Then you can filter on tag 2 anywhere you want into the network. Its also a good way to see how routers are learning what routes and from who.

-David

[Giuseppe Larosa · Accepted solution]

Hello @AndreaC ,

you have done half of the job with the route tags

On R1 and R3 I created 2 route-maps to prevent any loops (I'm not 100% sure if it works):
- set tag 10 for redistribution eigrp 30 to eigrp 10
- deny tag 10 and generic permit for redistribution of eigrp 10 to eigrp 30

Your route-maps should :

deny routes with route-tag set when redistribution has occurred on the other EIGRP process

permit routes without that route tag and tag them with a value to be used for deny on the other process

You need to use two route tags values

route-map EIGP30-into-EIGRP10 deny 10

match tag 10

route-map EIGP30-into-EIGRP10 permit 20

set tag 30

And:

route-map EIGP10-into-EIGRP30 deny 10

match tag 30

route-map EIGP10-into-EIGRP30 permit 20

set tag 10

Hope to help

Giuseppe