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seek_1992
Beginner

BGP Diverse-path/Add-path

Hi all,

 

I am trying to lab a scenario for L3VPN where I do have a BGP VPNv4 RR and multihomed customers (CEs).

I wonder if we can utilize the mulitpathing using BGP diverse-path (IOS XE) or BGP Add-path (IOS XR) on the RR without changing the RDs.

The following is the XE related configuration which is now my concern right now.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bgp/configuration/xe-3s/irg-xe-3s-book/irg_diverse_path.html#d258519e1163a1635

The document uses the IPv4 unicast AFI/SAFI where we need to have the same configuration for the VPNv4.

I have configured the following configuration on my BGP VPNv4 RR. However, the additional path (diverse path) is not advertise to the PE peer where is my case its IP address is 44.44.44.44. Following is the config of the VPNv4 RR:

router bgp 200
bgp log-neighbor-changes
no bgp default ipv4-unicast
neighbor 44.44.44.44 remote-as 200
neighbor 44.44.44.44 update-source Loopback0

address-family ipv4
exit-address-family
!
address-family vpnv4
neighbor 44.44.44.44 activate
neighbor 44.44.44.44 send-community extended
neighbor 44.44.44.44 route-reflector-client
neighbor 44.44.44.44 advertise diverse-path mpath
maximum-paths 4

 

In the meantime, the doc states to use the maximum-path ibgp 4 where the "ibgp" term is available only under IPv4 unicast AFI/SAFI and not the VPNv4 AFI/SAFI.

 

 

any feedback or help is much appreciated.

Regards

 Seek

3 REPLIES 3
seek_1992
Beginner

anyone! :D
Vaclav.Pokorny4
Beginner

Hello,

there are ways you can do it.

 

1 Additional path

2. Best-external

 

Can you share the configuration of other routers and show route for VPN4 on RR ?

 

Elvin Arias
Beginner

Not straightforward reply on this one, as BGP PIC Edge (add-path) would only advertise paths that are, by definition, different.

Diverse-path is another kind of feature (which I have to admit I haven't seen it use in production anywhere, yet) usually used to perform something called Shadow Route Reflection (RR). A Shadow RR is simply a redundant RR that by using the diverse-path feature will advertise the secondary best path instead of the primary, allowing the topology to have diversity of paths overcoming the default behaviour of BGP of only advertising the best path.

This works even if the paths are considered same, that in VPNv4/v6 BGP, means same route distinguisher (RD) values. I assume you have the same RD received by your RR, since if the RDs are different for prefix x.x.x.x, separate best path selection will be run and BGP will select and advertise both anyways.

The mpath option will select the second best path in the multipath and avertise it accordingly.

Can you post the topology, as well as the following:

1. show bgp vpnv4 unicast all <PREFIX> - in the shadow RR.

Elvin
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