[c-nsp] interesting ASR 9k bgp multipath issue

[John van Oppen]

ah, I guess I did not realize the difference if iegp load sharing.  Thanks all for pointing that out, good thing for a Monday.

-----Original Message-----
From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com] 
Sent: Monday, March 31, 2014 9:39 PM
To: John van Oppen; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] interesting ASR 9k bgp multipath issue

 
>Yes, I did, but my point is that behavior is not the same or at least 
>appears not to be the same on IOS, I want ibgp multipath but only for 
>things with matching IGP metrics, is there a way to tweak that.

IOS also behaves the same if configured the same (with maximum-paths eigbp).. as Jared pointed out, you want to enable "maximum-paths ibgp <n>"
(and possibly "maximum-paths ebgp <n>" if you also want to load-share eBGP peers). 

the configuration of
 maximum-paths eibgp <n>
is not a shortcut for and hence is different to  maximum-paths ibgp <n>  maximum-paths ebgp <n>


	oli


>
>-----Original Message-----
>From: Oliver Boehmer (oboehmer) [mailto:oboehmer at cisco.com]
>Sent: Monday, March 31, 2014 11:26 AM
>To: John van Oppen; cisco-nsp at puck.nether.net
>Subject: Re: [c-nsp] interesting ASR 9k bgp multipath issue
>
>
> 
>>so, I have some internally anycasted prefixes (DNS resolvers) as well as
>>bgp maximum paths set to allow both ibgp and ebgp multipath.   Oddly, as
>>you can see below the multipath appears to think two paths are 
>>identical even when they have different IGP metrics (path #1 and path 
>>#2), any idea
>>if this is a bug or how to fix it?    Obviously if the IGP cost is the
>>same it should load share, but if not it really should not be doing 
>>what is shown below since the paths are not equal.
>
>John, what exactly did you configure in your BGP address-family? It 
>looks like you enabled "maximum-paths eibgp <n>", which also considers 
>paths with different metrics as multipath candidates.
>
>	oli
>