EIGRP between routers and making one router preferred

[the_crooked_toe]

4507 = Louisville core (192.168.187.1)

2851 = Louisville MPLS (192.168.187.252)

3660 = Louisville Point-to-Point (192.168.187.254)

2821 = Lexington MPLS (192.168.13.1)

3640 = Lexington Point-to-Point (192.168.13.3)

The MPLS connection is the primary connection. The Point-to-Point is the backup connection.

I have EIGRP 101 running on every single router, and BGP only running on the MPLS routers between cities.

The 4507 has both the 2851 and the 3660 plugged into it.

If I add a network to the 4507, both of the routers should say something like 'D 10.110.115.0/24 [90/3072] via 192.168.187.1' correct?

The problem I am receiving is that when I add a network to the 4507 router and do a 'sh ip route' on the 2851, the route says it's reachable via the MPLS. It is not saying it's connected to the 4507. It's actually going from the 2851 to the 2821, to 3640, to 3660, then to 4507.

How do i stop this loop? I would like to do this without setting a static ip route.

Also, If i unplug the 3660 and add the network, the 2851 finds the advertised route from the 4507 with no problems. When I plug the 3660 back in, the route starts going back to saying its reachable via the MPLS connection.

Any help or ideas are greatly appreciated.

Thanks

[Giuseppe Larosa]

Hello Kendrick,

this command has to be given in interface configuration mode here is the beauty of the whole thing

see

router#conf t

Enter configuration commands, one per line. End with CNTL/Z.

router(config)#int f0/0

router(config-if)#?

router(config-if)#ip summary-address eigrp 100 172.16.0.0 255.255.0.0 ?

<1-255> Administrative distance

So you can have control of what routes are sent on backup point-to-point links

Until a most specific route is received over the MPLS Link it should be used even if it is a D EX because the most specific route is used first and then if two prefixes with same len exist it compares AD and metric

Hope to help

Giuseppe

[the_crooked_toe]

Thanks Guiseppe,

I need every network on every link. Except, I need the MPLS to be the primary.

So Do I need to do 'ip summary-address...' for every single network i want to advertise?

I'm not completely understanding how this is going to work.

So if I do this on the 4507, will the 2851 know those networks are attached to it via EIGRP.

[Giuseppe Larosa]

Hello Kendrick,

the feasibilty of what I'm suggesting depends from your current address plan:

a hierarchical address plan allows for summarization: a summary route still allows you to reach remote sites' ip subnets but with less details.

You can summarize if this doesn't create ambiguity:

example

if 172.25.14.0/24

172.25.15.0/24 are both associated to site M

from the other side point of view

routing to both happens in the same way

so a summary route of 172.25.14.0/23 that will take both in a single entry still allows to reach hosts in 172.25.14.0/24 and in 172.25.15.0/24 but with less detail.

If you can put your routers in the same scenario the detailed routes via MPLS Links will be preferred and used until they are alive.

If instead

172.25.14.0/24 belongs to site M

172.25.15.0/24 belongs to site N

if you create an aggregate 172.25.14.0/23 you can create problems.

If your address plan doesn't allow for some summarization other solutions are needed.

You may even think to use a second EIGRP process on backup links and have it redistributed into the main EIGRP process.

But I think you should be able to perform some summarization: the requirement is not to create a single prefix that will represent site M but few less specific routes.

Hope to help

Giuseppe

[the_crooked_toe]

Giuseppe,

I'm still not clear on how this is going to help me out. I'm not sure how this will get the 2851 to look to the 4507 for routes.

the 2851 should look to the 4507 for EIGRP routes.

The 3660 looks at the 4507 for EIGRP routes. But the 3660 is also connected to Lexington which is giving me the looping problem.

So how do I fix the AD problem so the 2851 looks to the 4507 for the EIGRP routes instead of looking at the loop?

thanks

[Giuseppe Larosa]

Hello Kendrich,

if I understand correctly your scenario:

2851 ----- MPLS ------- 2821---

4507 ----| |---4507

3660------ p-t-p ------ 3640---

EIGRP <> BGP <> EIGRP

EIGRP ------------------------------ EIGRP

where <> means redistribution

on the remote 2821 you need to filter the EIGRP routes so that into BGP only the local site routes are redistributed

You need to add a route-map with a prefix-list and only prefixes matching the prefix-list are to be reditributed

the loop is formed by the point-to-point link providing in the EIGRP of the remote site the same prefixes of the local site.

c2821

router bgp your.AS

redistribution eigrp your.EIGRP:AS route-map filter-routes

route-map filter-routes

match ip address prefix-list loca-routes

you need to filter everywhere

What I was suggesting is also beneficial because if out the point to point less specific routes are injected they cannot compete with local routes in doing the whole tour: it is the point-to-point link that provides a leakage path for local sites routes but if they are sent out less specific they again cannot compete with the legitimate routes coming over the MPLS link.

Probably this was suggested already by Jon the filtering based on site routes.

I would implement both methods to provide a complete control.

Hope to help

Giuseppe

[the_crooked_toe]

ok i understand what you are saying about filtering from the routes.

Attached is the network topology.

i hate asking for handouts but can you tell me if this is the correct commands I should be putting in my 2821

conf t

route-map Filter-Routes

how do i create a pre-fix list? Which pre-fixes should I be putting in this list? The local only prefixes?

router bgp 64803

redistribution eigrp 101 route-map Filter-Routes

what do i need to remove from the current configuration? jpg attached with config

[Giuseppe Larosa]

Hello Kendrick,

follow Jon's instructions in his today's posts you need first of all to fix the wrong redistribution of EIGRP into BGP that is creating the misbehaviour.

Then later, you can work on the way to make the backup links really backup.

Hope to help

Giuseppe