Distribute default route to eigrp stub neighboer

Answered Question
Jan 3rd, 2008

I have stub routing configured for some of our remote routers. One of the perks of stub routing is that you don't have to have a full route table at the remote router. All you need is a default route to the distribution router. I have not found a way to do this yet. Does anyone have an answer?

To summarize, I want to distribute a default route to my eigrp stub router.

Thanks in advance.

I have this problem too.
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Correct Answer by Jon Marshall about 8 years 11 months ago

Timothy

Option 2 doesn't assume the existence of a default route.

The reason i needed to check the docs was that an "ip summary-address eigrp.." installs a local route on the router you have used the command on

0.0.0.0 0.0.0.0 Null0

This route has an AD value of 5 which is better than internal EIGRP - AD 90 and external EIGRP AD 170. If the same router was already receving a default route from somewhere else this route pointing to Null0 with an AD of 5 would be better and so all traffic would be blackholed.

However if you don't have a default route you should be fine as there will always be a longer match.

Yes, your remote router should only have locally connected plus a default route.

Jon

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Jon Marshall Thu, 01/03/2008 - 15:47

Hi Timothy

There are 2 ways to do this

1) Assuming you don't already have a a default route configure a default route in your central site and add "redistribute static" under your EIGRP config. You can then use a distribute-list under the EIGRP config to only allow the default-route to be advertised to the remote routers.

If you already have a default route just use a distribute-list.

2) under the interface that connects to the remote site

ip summary-address eigrp "AS number" 0.0.0.0 0.0.0.0 5

This will advertise the default route and suppress any more specific routes.

From memory i think Cisco recommend against option 2 but i can't remember why - i'll have a look at the docs.

** Edit - okay you need to be careful with option 2. If you already have a default route in your HQ site then if you use option 2 you need to change the command to

ip summary-address eigrp 1 0.0.0.0 0.0.0.0 250

Apologies for that - i should have checked docs first.

Jon

timothykerr Thu, 01/03/2008 - 15:55

Jon,

Thanks for the reply. We do not have a default route in place, we use EIGRP to perform all routing. Because we have multiple redundant links for all of our distribution routers, it would be somewhat cumbersome to use default routes, and redistribute those.

I do like the idea of option number 2. Does option number 2 assume that you already have a default route? Or does it summarize all routes to 0.0.0.0 0.0.0.0 and then send it out? If so, then my routing table on the remote router should be empty (except for locally connected routes and the default route), right?

Thanks for your quick response!

Correct Answer
Jon Marshall Thu, 01/03/2008 - 16:01

Timothy

Option 2 doesn't assume the existence of a default route.

The reason i needed to check the docs was that an "ip summary-address eigrp.." installs a local route on the router you have used the command on

0.0.0.0 0.0.0.0 Null0

This route has an AD value of 5 which is better than internal EIGRP - AD 90 and external EIGRP AD 170. If the same router was already receving a default route from somewhere else this route pointing to Null0 with an AD of 5 would be better and so all traffic would be blackholed.

However if you don't have a default route you should be fine as there will always be a longer match.

Yes, your remote router should only have locally connected plus a default route.

Jon

timothykerr Thu, 01/03/2008 - 16:05

Jon,

Thank you for the information. It's funny how you can spend hours surfing the web and not find any answers to your questions, or you can post a topic in a forum here, and get it answered in about 20 minutes. So thanks again.

Tim

Jon Marshall Thu, 01/03/2008 - 16:16

Tim

No problem, glad to have been of help and appreciate the rating.

Jon

Jiri Votruba Wed, 10/30/2013 - 22:16

Jon,

I am trying to do pretty much the same thing as Timtohy. I have bunch of spoke routers that get connected to central hub router via a VTI Tunnel. I would like to see just the default route on all the spokes. The hub router is used for terminating VPNs from the spokes and is direclty connected to the core switch (6509) which has configured default route. The default route is redistributed so the hub VPN router learns this default route from the core switch as External route with AD 170:

VPN_hub_router#sh ip route | i 0.0.0.0

Gateway of last resort is 10.32.96.3 to network 0.0.0.0

D*EX  0.0.0.0/0 [170/1732352] via 10.32.96.3, 00:15:20, GigabitEthernet0/0

After reading your post I went ahead and configured ip summary-address eigrp 100 0.0.0.0 0.0.0.0 on the Tunnel interface of the hub router facing the spoke. Note here, I didn't not have the option of changing the AD to 250. The only option I have is to use a leak-map:

VPN_hub_router(config-if)# ip summary-address eigrp 100 0.0.0.0 0.0.0.0 ?       

  leak-map  Allow dynamic prefixes based on the leak-map

 

So I just used "ip summary-address eigrp 100 0.0.0.0 0.0.0.0" and I was expecting to see the new "blackhole" route pointing to Null0 in the routing table of the hub VPN router but to mu supprise it was not there. Could you or anybody else explain why it is not showing up and how come I could not asign the "floating" AD of 250 please?

BTW, the above delivered what I wanted initially and that was that my spoke router was only learning default route through EIGRP that points to the Tunnel interface of the hub VPN router.

Spoke_Router#sh ip route eigrp

Gateway last resort is 10.254.237.25 to network 0.0.0.0

D*EX  0.0.0.0/0 [170/26905856] via 10.254.237.25, 00:42:14, Tunnel1

Jiri

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