Mpls bgp soo


Can you please explain how the BGP SSO feature works when used in a MPLS VPNv4 environment? I understand that it’s configured on the PE routers where the same client is connected and using the same BGP AS number at two or more sites. And we tag the routes when they are being advertised by the client. However, how exactly does the PE routers prevent the loops?

Thank you

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Hi Victor,

Take a look at the topology in this lesson:

Imagine we add a “backdoor” link between CE1 and CE2. This will introduce a potential loop. It’s possible to advertise a prefix from CE2 > CE1 > PE1 > PE2 and back to CE2.

BGP SOO is a community attributes that is assigned to prefixes that the PE receives from a CE router. This can be used to prevent the PE router from advertising a prefix to a CE router that originated it.

I’ll add a configuration example for this later.


HI Rene,

I am not cleat about the concepts and how does it work - BGP soo. I need to understand BGP soo in detail. Appreciate if you can provide a tutorial asap.

Hi Abdus,

I will add an example later. Basically, BGP SoO is needed when you have a PE-CE topology where there is a “backdoor” link between the two CE routers. You don’t want routes to loop from CE1 > PE1 > P > PE2 > CE2 and back to CE1 (or vice versa). SoO is used as “tag” to prevent routes from looping around.

Thx Rene for your reply. Waiting for the tutorial.