Router Bridged Interfaces

[francis fox]

Hello Group, I have a pair of 4331 ISR routers connected together. Each router is connected to a WAN interface, one active the other standby. I have EIGRP running out of the WAN interface. I want to prefer the active WAN interface, over the standby in EIGRP so I could use metrics to achieve that. The interface between the routers is bridged so the WAN interfaces are in the same subnet. Does this sound feasible? I would like to use a FHRP to present a virtual IP for the WAN interfaces. Then I wouldn’t need to play with routing metrics.  But I don’t think this is going to be possible. Can the group offer some advice here? Thanks 

[paul driver]

Hello
The preferred way to manipulate eigrp path would be interface delay however prior to doing so can you post a diagram on your existing topology and if possible running configuration of both rtrs.

[Richard Burts]

The WAN interfaces being bridged makes this a pretty unusual situation. It would help if we had more information about this environment. But I believe that with limited information we can address part of your question. You ask "I would like to use a FHRP to present a virtual IP for the WAN interfaces". The purpose of FHRP protocols is to handle incoming traffic, presenting a virtual IP to the devices sending traffic over this connection. But you are running EIGRP. EIGRP establishes neighbor relationships based on physical interface IP addresses and not using any virtual address associated with the interface. So each of your routers will advertise to its neighbor with the interface address. I do not see that FHRP will achieve what you want.

[Giuseppe Larosa]

Hello @francis fox ,

the right tool wih EIGRP is to increase delay.

In your case to make the primary router more attractive the secondary router has to send EIGRP advertisements with a higher delay.

You have to increase delay on the internal facing interface(s) on the secondary router.

Start with show interface type x/y

look for the listed delay

then enforce an higher delay on LAN interfaces of secondary router.

Delay is configured on tens of microseconds at interface level.

This way the remote side routers will prefer the primary router as you would like to achieve.

Hope to help

Giuseppe

[francis fox]

All, thanks for your advice, much appreciated. I've attached a topology diagram if that helps clarify my questions.

[Giuseppe Larosa]

Hello @francis fox ,

seeing your topology diagram the scenario is more complex then I had thought in my previous post.

I have a question for you that can help to clarify if is possible with EIGRP metric tweaking to achieve the desired results

On your routers have you got two BVI interfaces and two subnets connecting your routers to the two pairs of WAN routers primary and secondary or all of them share a single subnet?

In the first case you can play with delay on the secondary WAN IP subnet increasing it,  but if all these devices are in a single subnet I am afraid it is difficult to play with EIGRP metric. ( offset-lists per neighbor could be used)

Another point that needs to be clarified is the type of MPLS service you are using:

are the WAN routers connected via an MPLS L3 VPN service or via a L2 VPN service.

Finally are the WAN routers primary and secondary under your control or under SP control ? I see the NTE near them this means Network Termination Equipment so they are owned by the provider ?

Hope to help

Giuseppe