Best way to advertise a default router to a stub?

[Andy White]

Hello,

I am setting up a small hub/spoke network with EIGRP as the routing protocol, what is the best way to advertise from the hub the a default route?  On the spokes I'm just using the 'eigrp stub' command.

Thanks

[paul driver]

Hello Andy,

As this is a stub and connected and summary's are allowed you can use the ip summary-address eigrp xxx 0.0.0.0 0.0.0.0 on the interface facing the stub router.

others include:

Candidate-default route

interface Loopback12

ip address 12.1.1.1 255.0.0.0

router eigrp 700

network 12.0.0.0

ip default-network 12.0.0.0

Default route

ip route 0.0.0.0 0.0.0.0 X.X.X.X ( towards WAN)

access-list 10 permit 0.0.0.0

router eigrp 700

redistribute static

distribute-list 10 out static

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[Andy White]

Let me try this today and I will let you know how I get on, many thanks!

[Andy White]

I see you used an access list on the last example which my book doesn't use, basically does this just define the interested traffic that can use that route?

[Bilal Nawaz]

Hello Andy,

Paul's example, the ACL is used to control and suppress the networks to be advertise out in updates apart from the permitted.

Here he as permitted the 0.0.0.0 which is a default route.

Remember you have redistribute static, by default advertises all static routes which may be undesired. Therefore Paul has demonstrated control over routing updates and advertisements for static redistribution.

You can also use a prefix list for this.

I'm sure you could use the

Redistribute static route-map xxxx metric

Command to achieve the same? This is the way I would do it.

Hope this helps

Sent from Cisco Technical Support iPhone App

[Peter Paluch]

Dear friends,

Paul's and Bilal's suggestions are very good. Indeed, if a default route to a stub router is to be advertised in EIGRP, I would go with the ip summary-address eigrp 700 0.0.0.0 0.0.0.0 command.

Personally, I strongly advise against using the ip default-network command. This command was created as a kludge around a particular IGRP limitation, and its use in EIGRP is cumbersome at best. I even have a feeling that the command is not working in 15.x IOSes anymore (it is present but the candidate default flag does not seem to be honored by EIGRP).

When filtering routes, I always prefer prefix lists to access lists. Using prefix lists is clearer in the intention, and also they are much more suited to perform prefix/netmask filtering. In addition, I suggest changing Paul's example a little: instead of redistributing all static routes into EIGRP and subsequently advertising just a single route out of all redistributed static routes, let's make sure we redistribute only the default route:

ip prefix-list Static2EIGRP permit 0.0.0.0/0
!
route-map Static2EIGRP permit 10
 match ip address prefix-list Static2EIGRP
!
router eigrp 700
 redistribute static route-map Static2EIGRP

If performing summarization, it is necessary to keep in mind that along with each advertised summary route, EIGRP installs a discard route pointing to Null0 into the summarizing router's routing table. This discard route has a default administrative distance of 5 and may actually override a different network if such network is present, leading to a loss of connectivity. In this particular example, the hub router summarizes networks into 0.0.0.0/0 towards spoke routers. If, however, the hub router itself has its own default route 0.0.0.0/0 learned via EIGRP or some other routing protocol, this learned default route will be replaced by the automatically installed discarding default route, and the connectivity provided by the original default route will be lost. This can be corrected by specifying that the administrative distance of the discard route is higher than the administrative distance of the currently correct default route on the hub in the ip summary-address command, e.g.:

ip summary-address eigrp 700 0.0.0.0 0.0.0.0 254

My two cents...

Best regards,

Peter

[Bilal Nawaz]

Hello Peter, i agree with the method, also you have made some great points here and have informed us of things I didn't know, I will rate your post accordingly. Always a pleasure to read your posts. Thank you.

Sent from Cisco Technical Support iPhone App

[Peter Paluch]

Hi Bilal,

Both you and Paul have given wonderful answers, and I am thankful to you guys for keeping up the great work here. I am honored by your kind words!

Best regards,

Peter

[Andy White]

Many thanks guys, some amazing answers.  I'm on my CCNP Route track (passed Switch) and this is very informative not only for my work but my studies too.

[Andy White]

Sorry about this, I have just tried this on my lab before I try it in production, but the spoke doesnt recieve the default route to the hub:

ip prefix-list Static2EIGRP permit 0.0.0.0/0
!
route-map Static2EIGRP permit 10
  match ip address prefix-list Static2EIGRP
!
router eigrp 700
  redistribute static route-map Static2EIGRP

access-list 10 permit 0.0.0.0

[Peter Paluch]

Hello Andy,

I have just tried this on my lab before I try it in production, but the spoke doesnt recieve the default route to the hub:

Hmm - do you have a default route on your hub router already present in the routing table? The above configuration relies on the default route being known to the hub router as a statically configured route (therefore the "redistribute static" command).

How does your hub router currently learn about the default route?

Best regards,

Peter

[Bilal Nawaz]

Hello Andy,

I also suspect that you do not have a default route on your hub router. The configuration specified requires you to have a static default route present in your routing table.

Its not like the default-information originate command where the routing protocol automagically injects a default route in its routing updates to peer's and neighbors.

With the configuration present it kind of behaves like this, broken in to sections:

• I have a prefix list that defines 0.0.0.0/0
• I have a route-map, and its condition is to match my prefix list (0.0.0.0/0)
• I have redistribution (under EIGRP) of static routes that are in the routing table ONLY defined by the route-map for specific prefix's

So in other words, if i dont have my default route in the routing table, it wont match the condition of being successfully installed route in the routing table. Hence it wont be advertised.

Lets take a look at some debugs and see what happens when my HUB router does not have a default route (i.e. take it out):

As stated in the output here, as soon as i removed my static route, EIGRP complains saying  0.0.0.0/0 "not in IP routing table"

When I put it back:

It started advertising the default route out of fa0/0 which my spoke router is connected to.

Hope this helps

Please rate useful posts & remember to mark any solved questions as answered. Thank you.

[Andy White]

Nice info once again, did you turn on a certain debug for that infor to show up as I didn't get that message to say 0.0.0.0/0 wasn't in the routing table as that would of helped me as once again you guys were spot on as I had missed this default route off, as soon as I put it on all worked.

I'm a little cloudly as you guys have been great and given me many options to use, so I have noted them all down and tested them.  I was just wondering which one is most commonly used with EIGRP in the field?  With OSPF I guess the common command is the default-information originate?

Thanks

[Bilal Nawaz]

Hello Andy, yes - I had the debug ip eigrp X where x is the AS number.

As Peter has mentioned, and also my recommendation is to use the redistribute static route-map option, with a prefix list associated to the route-map. It's more of a granular type of configuration. I'm not sure about which is commonly used out there. I haven't had enough experience at different organisations to comment on that, perhaps Peter, Paul or Antonio can comment on that.

With OSPF you have certain features for this type of scenario. Rather than the default information originate option which advertises to all OSPF speaking routers within parameters, you can configure an area as a stub area or totally stubby area or not so stubby area.

This is a great way to advertise a default route/summaries and filter out certain LSA types with only giving the spoke one direction to go, depending on which method you go for.

One of my favourite teachers presents OSPF Area types - imho MUST WATCH!!! He's funny too!

http://www.youtube.com/watch?v=1ScQYR7Gltw

http://www.youtube.com/watch?v=EycG7nc0WoA

Investigate OSPF for sure, I think it would be of benefit.

Hope this helps

Please rate useful posts & remember to mark any solved questions as answered. Thank you.

[Andy White]

Thanks, I like the way you can control things better with the route-map option which I had never used before, as I have found that it is easy to advertise routes to areas that may not need to know about these routes, you seem to have a lot of control.

Just an off topic question, I'm just testing all this in GNS3 first, but I am trying to make some of my spoke links have slowing bandwidth to change the FD etc, how do I do this as adding the bandwidth command didn't change the FD?  Would I have to mess withthe delay?

Thanks again and thanks for the youtube links as I've not heard of him.