This topic is to discuss the following lesson:
Thanks Rene, great lesson! Regarding the “disable-peer-as-check
”, could an another option to use be the “as-override
” command? If not, why?
Hello Mohammed
You bring up a very good point, these two commands are similar but they do two different things.
disable-peer-as-check
: Bypasses the BGP loop prevention mechanism that rejects routes containing the local AS in the AS_PATH. This is critical in asymmetric routing scenarios (e.g., data center interconnects where routes traverse the same AS multiple times).
as-override
: This is used primarily in MPLS/VPN setups to replace a customer’s AS number with the provider’s AS in the AS_PATH. This allows sites with the same AS to accept routes as if they originated locally, avoiding standard eBGP AS_PATH loop checks.
as-override
modifies the AS_PATH (replacing the peer’s AS with the local AS), whereas disable-peer-as-check
preserves the original AS_PATH but disables loop checks.
For VXLAN Underlays using eBGP like the one in the lesson, the disable-peer-as-check
is preferred. In such a two-AS eBGP underlay, routes are exchanged directly between Spines and Leafs (no duplicate ASes). The primary issue is the AS_PATH validation when route reflection is used. disable-peer-as-check
solves this by allowing Spines to advertise routes to Leafs with the same AS number. as-override
may break the AS_PATH structure and is unnecessary in this topology since there are no duplicate ASes to override. The following lesson shows an example of where as-override
is useful.
I hope this has been helpful!
Laz
Hi Renee,
Thank you for VXLAN series.
Do you session which explain how vxlan fabric can have border leaf config and eBGP to external WAN router?
Thanks
Richita
Hello Richita
At this point, Rene doesn’t have a lesson that describes a border leaf configuration with an eBGP connection to an external WAN. However, if this is a lesson you’d like to see on the site, you can make your suggestion at this Member Ideas page:
There you may find that others have made similar suggestions, and you can add your voice to theirs.
I hope this has been helpful!
Laz