I couldn’t resist using all of those acronyms.
EIGRP – Enhanced Interior Gateway Routing Protocol
MPLS – Multiprotocol Label Switching
VPN – Virtual Private Networking
PE-CE – Provider Equipment – Customer Equipment
SOO – Site Of Origin

MPLS Fundamentals pp. 220-226


Advertisement of the SOO BGP extended community attribute is used to identify routes that have originated from a site so that they are not re-advertised back into the same site. Each SOO uniquely identifies the site and allows for the routes to be filtered. SOO filtering is configured at the interface level. It is commonly used when a site contains both VPN and back door links.

From the Cisco document:
The configuration of the SOO extended community allows MPLS VPN traffic to be filtered on a per-site basis. The SoO extended community is configured in an inbound BGP route map on the PE router and is applied to the interface with the ip vrf sitemap command. The SOO extended community can be applied to all exit points at the customer site for more specific filtering but must be configured on all interfaces of PE routers that provide VPN services to CE routers.

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