BGP default route

Unanswered Question
Apr 12th, 2008


I have a issue because I have a single router for do multihomed, this router haven't enough ram memory (256 MB) for full table. My peers send me two default route but I want load sharing because now only out by a peer.

How can I load sharing with this scheme ?

Thank you,


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Overall Rating: 5 (1 ratings)
Paolo Bevilacqua Sat, 04/12/2008 - 09:50

From one peer, accept by fiter just some as paths that you want to reach that side. Use default to the other. That's for outgoing, incoming could load share by itself.

redcoruna Sat, 04/12/2008 - 10:03

That's what I thought, but if that down neighbor sends me the default route?

Paolo Bevilacqua Sat, 04/12/2008 - 10:31

You can always filter it out, or even better, have a local preference for another default.

redcoruna Sat, 04/12/2008 - 11:08

But the problem is that I haven't nothing in my routing table, you can see the command "show ip bgp":

Network Next Hop Metric LocPrf Weight Path

* ISP-A 0 0 AS(ISP-A) i

*> ISP-B 0 0 AS(ISP-B) i

If I set a route-map only to ISP-A how the following:

neighbord ISP-A route-map UPDATE-IN in

route-map UPDATE-IN permit 10

match ip address 1

set weight 200

access-list 1 permit RANGE MASK

Paolo Bevilacqua Sat, 04/12/2008 - 11:24

Sorry, long time has passed since I did BGP last time. Check if the ACl matches. Check the full bgp entry, what weight currently ? You can apply weight even directly on neighbor. Then you you have no routes, is because they are not sending any :)

redcoruna Sat, 04/12/2008 - 11:43

Thank friend.

I can't receive full table because my router have little ram :) . I go to will do with as-path. When I have done, I will post.

Harold Ritter Sat, 04/12/2008 - 13:51


BGP will not to load balance by default on paths received from different ASes. You will need the following command to change this default behavior:

router bgp

bgp bestpath as-path multipath-relax

You will also need to use "maximum-paths 2" as suggested by Edison.

This will allow you to load balance between the two default routes.


redcoruna Sat, 04/12/2008 - 15:37

Thank Harold and others,

But I need have a peer with in weight 100 and a default route and the other provider backup with a default route and a weight 50, and I will request to this provider a full table for filter two ASN with a weight 200.

I thought in this configuration, but I not am secure:

neighbor ISP-A weight 50

neighbor ISP-A route-map TIMOFONICA in

route-map TIMOFONICA permit 10

match as-path 5

set weight 200

ip as-path access-list 5 permit ^3352$

ip as-path access-list 5 deny ^$


Giuseppe Larosa Sun, 04/13/2008 - 11:47

Hello redcoruna,

if you want to receive a default route from ISP-A you need and additional route map block that allows it, otherwise you will see only the prefixes that have AS path = 3352

or also the default route will have weight 200 if its AS path = 3352

so you should add the following before:

ip prefix-list only-default permit

route-map TIMOFONICA permit 5

match ip address prefix-list only-default

this way you accept the default route but you have weight 50, the second block will accept with an increased weight all the other prefixes with AS path = 3352

best regards


redcoruna Tue, 04/15/2008 - 01:00


Very good posted, other idea if you ISP will not provide of full table + default route can be:

- Request full route and you create yourself a default route:





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