Listing all "multipath" routes

[Marek Manik]

Hi all,

i would like to check if it is worth enabling "maximum-path ibgp XY". I have ASR9K running 5.3.3.

I would like to check how many prefixes meet all criteria for ibgp multipath. (I assume there should not be that many, because it depends on topology and all path for particular prefix have to have the same BGP attributes including the same IGP cost to next hop and next hop have to be different )

Is there any command which can list all prefixes flagged with "multipath"? (Or at least how many they are.)

Thanks

marek

[Sakthi Malli]

show bgp <prefix> [detail] should list the prefixes with multipath. Like in the example below:

Note however the output is for eBGP prefix.

sh bgp 20.5.6.0
Wed Jan 29 13:08:54.458 EST
BGP routing table entry for 20.5.6.0/24
Versions:
Process bRIB/RIB SendTblVer
Speaker 5 5
Last Modified: Jan 29 13:08:39.000 for 00:00:15
Paths: (2 available, best #1)
Advertised to update-groups (with more than one peer):
0.1
Advertised to peers (in unique update groups):
20.20.20.20
Path #1: Received by speaker 0
Advertised to update-groups (with more than one peer):
0.1
Advertised to peers (in unique update groups):
20.20.20.20
101
5.5.5.5 from 5.5.5.5 (5.5.5.5)
Origin IGP, metric 0, localpref 100, valid, external, best, group-best, multipath
Received Path ID 0, Local Path ID 1, version 5
Origin-AS validity: not-found
Path #2: Received by speaker 0
Not advertised to any peer
101
6.6.6.6 from 6.6.6.6 (6.6.6.6)
Origin IGP, metric 0, localpref 100, valid, external, multipath
Received Path ID 0, Local Path ID 0, version 0
Origin-AS validity: not-found

You could also achieve UCMP (unequal cost Multi path) with BGP. This link provides more info: https://supportforums.cisco.com/document/137306/asr9000xr-understanding-unequal-cost-multipath-ucmp-dmz-link-bandwidth-and-routes

[Marek Manik · Accepted solution]

Thnx samallis,

but if I have full RT how can I list those which has "multipath" set? I can't check every prefix.

At least to know how many they are will still be enough. I didn't find any command for that.

I was also looking for any indirect way to check that. Can I simply rely on count in "sh route ipv4/6 summary"? If I have 50K routes candidates for "multipath", I should be able to see it.

There is no significant difference in "sh route ipv4/6 summary" if I enable it or not. So, I'm not so sure if I don't have that many multipath routes or I'm looking at wrong place.

thnx

MM

[Sakthi Malli]

"show route afi-all [vrf [all|word]] summary" only provides the total number of prefixes and wouldn't actually provide the ECMP paths that you like to see. 

Can you try the "show bgp scale" command with and without "maximum-path" config and see if you are able to see the change in number of "Paths"

RP/1/RSP0/CPU0:ASR9001-A#sh bgp scale

VRF: default

Neighbors Configured: 10     Established: 0     

Address-Family   Prefixes Paths    PathElem   Prefix     Path       PathElem 

                                               Memory     Memory     Memory 

  IPv4 Unicast    69       69       69         6KB        4KB        3KB        

  ------------------------------------------------------------------------------

  Total           69       69       69         6KB        4KB        3KB        

[Marek Manik]

yeap,

that's where I was looking as well. It looks we can't list all multipath routes easily. So i relied on fact, that if I have many such routes, it should have impact on BGP RIB/RIB.

Fo IOS, there is impact on memory, but didn't find anything written for XR

http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3s-book/ibgp_multipath_load_sharing.html

I'm closing this case for the moment. Enabling iBGP multipath itself doesn't have much value in my case.

btw, I was told that UCMP shouldn't be used on Internet routers. It may create loops in certain cases.. UCMP was designed for L3VPNs.

thnx anyway