All received RTC routes that are deemed valid are stored in the RIB-IN. An RTC route is considered invalid and treated as withdrawn, if any of the following applies:
The prefix length is 1-31.
The prefix length is 33-47.
The prefix length is 48-96 and the 16 most-significant bits are not 0x0002, 0x0102 or 0x0202.
If multiple RTC routes are received for the same prefix value then standard BGP best path selection procedures are used to determine the best of these routes.
The best RTC route per prefix is re-advertised to RTC peers based on the following rules:
The best path for a default RTC route (prefix-length 0, origin AS only with prefix-length 32, or origin AS plus 16 bits of an RT type with prefix-length 48) is never propagated to another peer.
A PE with only IBGP RTC peers that is neither a route reflector nor an ASBR does not re-advertise the best RTC route to any RTC peer due to standard IBGP split horizon rules.
A route reflector that receives its best RTC route for a prefix from a client peer re-advertises that route (subject to export policies) to all of its client and non-client IBGP peers (including the originator), per standard RR operation. When the route is re-advertised to client peers, the RR (i) sets the ORIGINATOR_ID to its own router ID and (ii) modifies the NEXT_HOP to be its local address for the sessions (for example, system IP).
A route reflector that receives its best RTC route for a prefix from a non-client peer re-advertises that route (subject to export policies) to all of its client peers, per standard RR operation. If the RR has a non-best path for the prefix from any of its clients, it advertises the best of the client-advertised paths to all non-client peers.
An ASBR that is neither a PE nor a route reflector that receives its best RTC route for a prefix from an IBGP peer re-advertises that route (subject to export policies) to its EBGP peers. It modifies the NEXT_HOP and AS_PATH of the re-advertised route per standard BGP rules. No aggregation of RTC routes is supported.
An ASBR that is neither a PE nor a route reflector that receives its best RTC route for a prefix from an External Border Gateway Protocol (EBGP) peer re-advertises that route (subject to export policies) to its EBGP and IBGP peers. When re-advertised routes are sent to EBGP peers, the ASBR modifies the NEXT_HOP and AS_PATH per standard BGP rules. No aggregation of RTC routes is supported.
These advertisement rules do not handle hierarchical RR topologies properly. This is a limitation of the current RT constraint standard.