How to use As-Override for BGP VPNV4 neighbors

Yvan.hua · ‎08-12-2021

How to use As-Override for VPNV4 neighbors when doing MPLS VPN Option B?
e.g.
(AS 100) R1 ----option b--- (PE1 --- PE2 )--- Option B --- R2 (AS 100)

marce1000 · ‎08-12-2021

- Check this article :

https://community.cisco.com/t5/networking-documents/understanding-bgp-as-override-feature/ta-p/3111967

M.

-- Each morning when I wake up and look into the mirror I always say ' Why am I so brilliant ? '
When the mirror will then always repond to me with ' The only thing that exceeds your brilliance is your beauty! '

Yvan.hua · ‎08-12-2021

Thank you for your reply
This post is also using as-override under "address-family ipv4 vrf".
If i use Option B between R1 and PE1, R1 and PE1 is a neighbor of VPNV4, not a neighbor of vrf

MHM Cisco World · ‎08-13-2021

MPLS Option B is between different SP AS, I see only two CE connect through one SP MPLS, so why Op B?

Yvan.hua · ‎08-16-2021

Hi all

Please see the picture, all SD-WAN devices belong to the same AS, used to connect customers, MPLS belongs to another AS, and the SD-WAN device cannot set up “allow as in” in the sd-wan portal, so i need to set as-override on PE.

Because PE and SD-WAN devices are using Oiption B, it is VPNV4 neighbor.
I can also choose Option a , but I prefer to use Option B.

If I cannot use As-Override for VPNV4 neighbors, then I have to use other ways, such as using Option A

@Giuseppe Larosa @MHM Cisco World

Giuseppe Larosa · ‎08-17-2021

Hello @Yvan.hua ,

your CE devices are actually SD WAN edge devices.

I don't understand the need for MPLS inter AS VPN with the service provider.

your SD WAN devices are using MPLS LSPs between them or point to point tunnels based on IP ?

In the second case all what the SP needs to propagate are the PE-CE links in order to route packets in IP based tunnels.

You can run MPLS over GRE p2p tunnels between SD WAN edge devices, so you could avoid to use MPLS VPN inter AS.

As an alternative if you really want to use MPLS in the forwarding plane between SD WAN devices the more appropriate design model should be Carrier Supporting Carrier CSC with all the regards to MTU settings for the added MPLS label overhead.

Hope to help

Giuseppe

Giuseppe Larosa · ‎08-13-2021

Hello @Yvan.hua ,

e BGP VPNv4 sessions should be done between public BGP AS numbers of the two MPLS SP so there shouldn't be a need for AS override on AF VPNv4.

Can you explain what is your scenario ?

Why you would like to use AS override in MPLS VPN inter AS option B ?

Hope to help

Giuseppe