BGP AS uniqueness for MLAG pair

  • 7 February 2019
  • 3 replies

In the Cumulus 3.7 documentation, the example shown on the MLAG page has a unique private bgp autonomous-system id per switch. The BGP page defines the autonomous system as a set of routers under a common administration. As it is hard to believe that the two halves of an MLAG pair would ever be in different administrative domains, what is the reasoning behind using an autonomous-system id per switch as opposed to per MLAG-pair?



3 replies

Userlevel 2
When using BGP in a data center, thr trtm "administrative domain" is not applicable anymore as you would see it for global bgp peering. As you said, two neighboring switches (mlag or not) wouldnt be managed by different organizations.

I would recommend reading the "BGP in the Datacenter" book. This explains it in more detail.
Userlevel 5
I generally recommend having both MLAG devices in the same AS for simplicity and an number of other reasons for EVPN and gateway advertisement. It also simplifies the BGP table when troubleshooting towards remote MLAG pairs.
Userlevel 4
Thanks for the help here guys!