Segment routing book, pg 184 says we need to implement RFC 7794 to determine the correct prefix original originator which needs PHP service from SR TE upstream router. The upstream router cannot determine if the downstream router in shortest path tree is also the prefix originator. The prefix could be a leak prefix. PHP service MUST be given only to downstream router to which the prefix is a local interface prefix and not to router which has leaked/re-advertises the prefix. In the later case, it would abruptly leads to SR tunnel termination at the router re-advertising the prefix which is not correct.
We need to implement RFC7794 which introduces the new prefix related flags - X, R and N bits through which upstream router can determine if the downstream router is an original prefix originator or not.
Currently this is not supported, so SR_TUNNELS originating from L2 node are not reachable to L1 node (prefix originator)
Segment routing book, pg 184 says we need to implement RFC 7794 to determine the correct prefix original originator which needs PHP service from SR TE upstream router. The upstream router cannot determine if the downstream router in shortest path tree is also the prefix originator. The prefix could be a leak prefix. PHP service MUST be given only to downstream router to which the prefix is a local interface prefix and not to router which has leaked/re-advertises the prefix. In the later case, it would abruptly leads to SR tunnel termination at the router re-advertising the prefix which is not correct. We need to implement RFC7794 which introduces the new prefix related flags - X, R and N bits through which upstream router can determine if the downstream router is an original prefix originator or not. Currently this is not supported, so SR_TUNNELS originating from L2 node are not reachable to L1 node (prefix originator)