I wanna ask about what is the actual use from appliy the Soo community on the incoming routes also how its working i mean how its attached and how its travel the path.
The Site of Origin attribute is used mainly to prevent routing loops for multihomed sites i.e. sites with multiple links to the MPLS VPN backbone. All routes learned from the site are then given this attribute so that the PE can uniquely identify which site the route came from. In such cases, all routes learned from that site must be given the same attribute, even if links from that site come in on different PE routers. When routes are learned from the site, they are propagated into BGP together with this attribute. Therefore, when advertising routes to the multihomed site, routes that carry the same So) attribute as the site will not be injected. This helps to prevent routing loops.
The SoO attribute is not used for singly homed sites.
In a nutshell, the So) attribute prevents a multihomed site from learning routes that it itself injected into the VPN.
Hope that helps - pls rate the post if it does.