Nexus BGP advertise-best-external feature available?

[Difan Zhao]

I was using advertise-best-external on ASRs to speed up convergence time. My topology is like

AS 123: Nexus1 --- Nexus2

         |            |

AS 456: ASR1   ---   ASR2

Nexus 1 only sees ASR's routes through the link (BGP peering) on the left side because of the metric setup (100 on the left side vs 200 on the right side). Nexus2 has the BGP routes from both the Nexus1 and ASR2. It won't advertise the route learned from ASR2 to Nexus2 because of the default behavior that it only advertises the best. On the IOS, with the "advertise-best-external", Nexus2 would also advertise the route learned from ASR2 (as it is the "best" external route, beside the best overall one). Therefore, in case of failure of ASR1, Nexus1 will already have a backup route in place and will be converged faster, rather than re-learning it from Nexus2. 

I can't see to find the command to enable it on the Nexus though. I only see the "additional-path" feature, which seems to be quite complex and overkill in our case.

Please let me know your suggestion.

Thanks!

Difan

[Georg Pauwen]

Hello,

there doesn't seem to be an exact equivalent in NX-OS.

'additional-paths install backup' is your best (and apparently only) option...

[Difan Zhao]

Thanks Georg. I assume that this "install backup" is to be configured on the Nexus1. Do I configure the Nexus2 to do "additional-paths send"? There is also "receive". Do I need it on any of the two Nexus?

[Georg Pauwen]

Hello,

to be honest I have never implemented this feature on the Nexus. I would say you need all three commands on all neighbors under the ipv4 address family:

additional-paths send
additional-paths receive
additional-paths install backup