Technical Documentation - Static VXLAN Tunnels


I was reading the following documentation (https://docs.cumulusnetworks.com/display/DOCS/Static+VXLAN+Tunnels#) and noticed that there are different BGP AS #'s being used for the spine's (backplane). Is this a mistake?

ECMP only works to the same AS # with the same metric's.

3 replies

Userlevel 1
1) BGP multi-path across diverse AS_PATH
in BGP there is a knob to modify the BGP bestpath algorithm and ignore the AS_PATH source (AS 100 versus AS 200) then you can use BGP multi-path across multiple AS numbers (assuming AS_PATH is equal length).

NCLU command is " net add bgp bestpath as-path multipath-relax "

It's true there's several path attributes that must be equal for the route path to be a candidate for multi-path

2) BGP multi-path using unequal cost
BGP supports multi-path, whether the paths have equal costs or unequal costs, though not all implementations support unequal-cost multi-path. It's on the roadmap for FRR routing suite (feel free to contact us through official channels if this is an urgent requirement).

https://docs.cumulusnetworks.com/display/DOCS/Border+Gateway+Protocol+-+BGP

Additionally you might find this ebook a helpful resource for BGP in the Data Center environment:
https://cumulusnetworks.com/blog/ultimate-bgp-guide/
Userlevel 2
In the case where multiple paths for the same prefix are learned via eBGP, and the only difference is the AS path, we can configure the following to allow both paths to be installed in the RIB:

Via NCLU:
net add bgp bestpath as-path multipath-relax

Via VTYSH:
router bgp 65020
bgp bestpath as-path multipath-relax

In this scenario, configuring multipath-relax would still allow ECMP to work through the spines even though they do not share an AS.
Thanks!

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