BGP to EIGRP route redistribution

[davidmorris1]

I have one router connected to the WAN MPLS network which redistributes BGP into EIGRP to the single core switch.

The is a second router connected to the same WAN MPLS network and is also connected to a backup network, which are also distributing BGP ino EIGRP for the core switch.

Traffic is load balance across both switch connections to the site routers and to the MPLS network.  I am wondering if the MPLS WAN circuit on the 2nd router goes down how do I let EIGRP know to prefer the EIGRP connection to the first router because the back up circuit is much slower and should only be used for failure of both MPLS WAN connections to the site.

Can this be done?

[Julio Carvajal]

Hello,

Not clear enough!

Can you try explaining this again with a network diagram.

We will help you afterwards.

Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2-CCNP, JNCIS-SEC
For inmediate assistance hire us at http://i-networks.us

[davidmorris1]

Julio,

Thanks for the reply.  Here is a drawing depicting my question.  Let me know if you need additional information.

Regards,

David

[Jon Marshall]

David

Sorry, I'm posting while I'm working it through which is never a good thing to do :-)

Following on from previous post do you have a default route anywhere ?

Jon

[Jon Marshall]

David

Just to clarify.

Your diagram says all 3 routers are doing BGP to EIGRP but then you also say router B is redistributing both it's BGP received routes from the MPLS peer and router C.

I suspect it is the latter but just wanted to confirm.

Is it fair to say router C should only be used if both A and B are down ?

If so by far the simplest solution, if you can do it, is to have router C advertise summary addresses for the remote subnets while A and B receive the more specific routes.

That way switch 1 will receive both the summaries and the more specific but will only use the summaries if it doesn't have more specific routes which would only happen if both A and B were down.

Is it possible to do this ?

Edit - you may already be advertising summary ranges from each specific site. But all you would need on router C is one summary address covering all the sites because it only comes into play when both A and B aren't receiving BGP routes from their MPLS peers.

Jon

[milan.kulik]

Hi Jon, what about using a route-map for BGP to EIGRP reidstribution on Router B? It could match the next-hop and assign a worse EIGRP metric to routes using Router C (.25) as the next-hop while a better EIGRP metric (the same as Router A is using) would be assigned to all other routes (i.e. those using the MPLS neighbor .13 as the next-hop). As only the best route is redistributed always, wouldn't that work as necessary? Best regards, Milan

[Jon Marshall]

Hi Milan

Haven't spoken you in a while :-)

I'm not sure I follow but it may well be me as you are usually right about these things.

As far as I know a route is only redistributed if it is in the IP routing table (RIB). Currently router B is receiving BGP routes from both it's MPLS peer and router C.

If you look at the document David posted it states that router B prefers router C for some networks. In which case for those networks BGP will select router C as the best path and install that in the RIB.

If you then redistributed those routes into EIGRP and assigned a worse metric the L3 switch would then only use router A when it actually should be using router B to get to router C.

If however all BGP routes learnt from the MPLS peer on router B were the preferred ones then yes I think using a route-map as you suggest would work.

It could be that I am misinterpreting what the document says or that I have misunderstood what you were saying.

Thoughts ?

Jon

[davidmorris1]

Jon,

You are correct there are some routes that BGP prefers the path to Router C.

Simplistically I what the net result to be like the interface Delay changing on Router B's interface to Switch 1 when the BGP neighbor .13 is down.

[Jon Marshall]

David

How do you ensure currently that the routes that should go via router C actually go that way ie.

if the same routes are received from the MPLS peers then router A also receives these routes. It then redistributes them into EIGRP.

This means the L3 switch sees equal cost paths via A and B but you don't want load balancing for those networks, you want all traffic to go to B and then C.

So how does that work ?

Jon

[milan.kulik]

Hi Jon, difficult to say without knowing more details. I guess if it would be possible to identify those routes preferred via router C, it might be possible to create an exception for them within the route-map and not to give them the worse EIGRP metric? Best regards, Milan

[Jon Marshall]

Milan

Why do I always feel like you are trying to catch me out :-)

It really does depend on -

a) the number of routes

and

b) whether they fall into the middle of a summary range

Not sure which option is best at the moment but yes I suspect it could all be done on router B as you suggest.

I haven't done route redistribution for a while.

Can you just confirm whether you can have multiple match statements in the same permit statement using a logical AND as that might well be the way to approach it assuming there are not a huge number of routes ie.

match the BGP peer IP together with an acl/prefix-list for those networks that should go via C and just redistribute

match the BGP peer IP only and set a higher metric so that when they are redistributed the metric is higher than the route via A.

Jon

[milan.kulik]

Hi Jon, I believe there is possible to have multiple match statements in the same permit statement - I've used that several times already (not the match next-hop actually, but there should be no exception for this command, I believe). BTW, it's described here: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfindp1.html#wp1018782 Best regards, Milan

[Jon Marshall]

Just found my own answer from a Cisco doc on redistributing using route-maps -

If several match commands are present in a clause, all must succeed for a given route in order for that route to match the clause (in other words, the logical AND algorithm is applied for multiple match commands).

Jon

[Jon Marshall]

Milan

Just to be clear, the fact that some routes should go via C would also mean my summary suggestion needs modifying to take this into account.

I didn't spot that part of the document until you posted your solution just in case you were wondering why I said your's won't work but mine would :-)

My mistake.

At the moment I'm not sure which is the best solution. It really depends on the amount of routes that need to go via C.

Jon

[davidmorris1]

A more accurate statement would be the 3 interfaces on Router A and B are redistributing BGP into EIGRP, in place of all 3 routers are doing BGP to EIGRP.

Yes, router C should be used when both Router A and B are down with the exception of the routers BGP prefers to Router C.

If I understand your summary suggestion I need to summarize all 9,000 plus routes from Router C, is that correct?  And if one route cannot be summarized then traffic would still flow across Router C for the unsummarized subnet when Router B was down and router A was still up.  Do I have that correct?