Redistributing static routes question

Answered Question
Jul 19th, 2007

Here is our situation:

- We use EIGRP in our WAN

- We have customers that connect to us via private line, but we do not control their router (and thus cannot make them peer with us via EIGRP)

- Currently we have a static route to them which we redistribute so that our other WAN sites can connect to them

- My question is:

We have implemented a backup site so our customer now has two routers (one at primary and one at DR). Both are T1s. Do I just redistribute the static route from the DR site as well? The primary site and DR site are connected via 100mb WAN link. For our WAN sites where we control both sides I set delay to be sure our primary site is preferred. But in this case where we don't control the other side, how can I set preference?

Thanks!

I have this problem too.
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Correct Answer by Richard Burts about 9 years 6 months ago

Jake

While it is a best practice that the delay should be the same on both ends of the link, that is not a requirement. Try setting it on your end and see what result it has. If it does not achieve what you want you can always use the manual control of configuring the metrics in the redistribute of the backup routes.

HTH

Rick

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Amit Singh Thu, 07/19/2007 - 06:39

Hi,

We would appreciate a network topology diagram to understand the sition more.There are two parts of you question, the answer for the first is that you have to redistribute the second static route from the DR site as well so that all the other WAN sites have both the routes to reach your customer.

I havenot really understood the second part of it. (maybe someone else can comment on that). The part which is unclear is " But in this case where we don't control the other side, how can I set preference? ".. Please explain this again with a little more detail and with a brief topology.

HTH,

-amit singh

jnewton03 Thu, 07/19/2007 - 06:45

Hi Amit,

Thanks for the quick response. What I mean is that we do not have administrative access to their router in our WAN. We give them an IP address on our WAN segment and then they NAT that to their internal network. The router sits in our data center. The CSU/DSU has a T1 back to their data center and the Eth interface connects to our WAN switch. We then have static routes on our WAN router to point traffic for their IP addresses to the WAN address that we give them (and they NAT). I'll see if I can draw something up real quick.

Thanks!

Richard Burts Thu, 07/19/2007 - 07:06

Jake

I am not clear from your description whether you are routing the same prefix for the customer via the "preferred" link and via the "backup" link. I assume that this is the case and if so there are a couple of solutions that might work. I would suggest first considering floating static routes. You would keep the existing static routes and you would configure the new backup static routes with an administrative distance higher than the default (of 1) so that if the primary static route is available it is used and if it is withdrawn from the routing table then the floating static route gets inserted into the routing table and could be redistributed. I would suggest that you make the administrative distance greater then the AD of EIGRP redistributed routes.

A second alternative would be closer to what your question is asking and would manipulate the metric of the backup static route. One version of the alternative would be to have the primary static route and the backup static route on the same router. You would then control redistribution of static routes with a route map. The route map would have one instance which would match the primary static routes and would set the default metric to some value of delay and would have a second instance which would match the backup static routes and would set the delay metric to some higher value. This would result in the primary static routes having a better metric and the backup static routes having a worse metric. The other version of this option is to configure primary static routes on one router and to configure the backup static routes on another router. On the router doing backup static routes you set a default metric for the static route redistribution that is worse than the default metric of the primary static routes.

HTH

Rick

jnewton03 Thu, 07/19/2007 - 07:18

"On the router doing backup static routes you set a default metric for the static route redistribution that is worse than the default metric of the primary static routes. "

Hi Rick,

This is what I was looking for and as I stated before, I do modify the metrics for WAN sites where I have access to both routers. I set a delay on the Serial Interfaces pointed to the backup site so that it has a worse metric than my primary site. However, since I could only set the delay on the interface of the router I control, would it still make it a backup route?

Richard Burts Thu, 07/19/2007 - 07:24

Jake

It might be sufficient to just set the delay on the interface higher. My thought had been to explicitly configure default metric under router eigrp (or to explicitly code the metrics on the redistribute statement so that you had manual control.

HTH

Rick

jnewton03 Thu, 07/19/2007 - 07:52

It was my understanding that to modify metrics using the delay commmand, you had to set delay on both ends of the WAN link. Is that not the case? Just setting it on my end should work?

Correct Answer
Richard Burts Thu, 07/19/2007 - 08:53

Jake

While it is a best practice that the delay should be the same on both ends of the link, that is not a requirement. Try setting it on your end and see what result it has. If it does not achieve what you want you can always use the manual control of configuring the metrics in the redistribute of the backup routes.

HTH

Rick

Richard Burts Thu, 07/19/2007 - 09:43

Jake

I am glad that my answers were helpful to you. Thanks for using the rating system to indicate that your issue was resolved (and thanks for the rating). It makes the forum more useful when people can read about an issue and can know that they will read something that resolved the issue. I encourage you to continue your participation in the forum.

HTH

Rick

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