# VXLAN Underlay eBGP Two-AS

**URL:** https://forum.networklessons.com/t/vxlan-underlay-ebgp-two-as/57002
**Category:** Lessons Discussion
**Created:** [May 7, 2025, 8:57am UTC](https://forum.networklessons.com/t/vxlan-underlay-ebgp-two-as/57002 "2025-05-07T08:57:51Z")
**Posts on this page:** 1
**Showing post:** 3

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### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis)
#### Post date: [May 14, 2025, 6:26am UTC](https://forum.networklessons.com/t/vxlan-underlay-ebgp-two-as/57002/3 "2025-05-14T06:26:15Z")

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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.

> **[MPLS Layer 3 VPN BGP AS Override](https://networklessons.com/bgp/mpls-layer-3-vpn-bgp-override)**
>
> BGP AS override allows us to change the AS number in outgoing BGP updates. You can use this in MPLS VPN scenarios where a customer is using the same AS.

I hope this has been helpful!

Laz

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