Establishing and advertising co-routed bidirectional paths across multiple domains
Establishing and advertising co-routed bidirectional paths across multiple domains includes determining a path from the router to a BGP peer, in a Segment Routing (SR) network, as a reverse path SR policy; appending a Binding Segment Identifier (BSID) of the reverse path SR policy in a BGP update message; and sending the BGP update message to the BGP peer. This can be used to ensure an Operations, Administration, and Maintenance (OAM) packet is guaranteed to traverse the same forward and reverse path for fault detection thereon.
1 . A router configured as a Border Gateway Protocol (BGP) speaker, the router comprising circuitry configured to:
determine a path from the router to a BGP peer, in a Segment Routing (SR) network, as a reverse path SR policy,
append a Binding Segment Identifier (BSID) of the reverse path SR policy to a Reverse-Label-Stack attribute of a BGP update message, wherein the append of the BSID contributes to construction of the Reverse-Label-Stack in a distributed manner as the BGP update message propagates, the construction involving each BGP speaker along the path appending a BSID of its installed reverse path SR policy, and
send the BGP update message to the BGP peer.
2 . The router of claim 1 , wherein the circuitry is further configured to
receive a packet having, as an active segment, the BSID from the Reverse-Label Stack, and
send the packet on the path based on the reverse path SR policy.
3 . The router of claim 2 , wherein the packet is an Operations, Administration, and Maintenance (OAM) packet including Bidirectional Forwarding Detection (BFD) or Seamless BFD (S-BFD) information, which is guaranteed to traverse a same forward and reverse path for fault detection by virtue of the co-routed reverse-path SR policy advertised in the BGP update message.
4 . The router of claim 1 , wherein, to determine the path, the circuitry is further configured to
compute a path from the BGP speaker to the BGP peer using a set of constraints for a color in a BGP color extended community.
5 . The router of claim 1 , wherein, to determine the path, the circuitry is further configured to
reverse a forward path of an SR policy which is from the BGP peer to the BGP speaker that was computed using a set of constrains for a color in a BGP color extended community.
6 . The router of claim 1 , wherein the SR network includes multiple domains, and wherein the router is one of a Border Router (BR) and a Provider Edge (PE) router.
7 . The router of claim 1 , wherein the reverse path SR policy further includes one or more prefix Segment Identifiers SIDs and the path includes one or more Equal Cost Multi-Paths (ECMPs), and wherein the circuitry is further configured to
test the one or more ECMPs to validate the path.
8 . A non-transitory computer-readable medium comprising instructions for programming circuitry associated with a router to perform steps of:
determining a path from the router to a BGP peer, in a Segment Routing (SR) network, as a reverse path SR policy;
appending a Binding Segment Identifier (BSID) of the reverse path SR policy to a Reverse-Label-Stack attribute of a BGP update message, wherein the appending of the BSID contributes to construction of the Reverse-Label-Stack in a distributed manner as the BGP update message propagates, the construction involving each BGP speaker along the path appending a BSID of its installed reverse path SR policy; and
sending the BGP update message to the BGP peer.
9 . The non-transitory computer-readable medium of claim 8 , wherein the steps further include
receiving a packet having, as an active segment, the BSID from the Reverse-Label Stack; and
sending the packet on the path based on the reverse path SR policy.
10 . The non-transitory computer-readable medium of claim 9 , wherein the packet is an Operations, Administration, and Maintenance (OAM) packet including Bidirectional Forwarding Detection (BFD) or Seamless BFD (S-BFD) information, which is guaranteed to traverse a same forward and reverse path for fault detection by virtue of the co-routed reverse-path SR policy advertised in the BGP update message.
11 . The non-transitory computer-readable medium of claim 8 , wherein the determining includes
computing a path from a BGP speaker to the BGP peer using a set of constraints for a color in a BGP color extended community.
12 . The non-transitory computer-readable medium of claim 8 , wherein the determining includes
reversing a forward path of an SR policy which is from the BGP peer to the BGP speaker that was computed using a set of constraint for a color in a BGP color extended community.
13 . The non-transitory computer-readable medium claim 8 , wherein the SR network includes multiple domains, and wherein the router is one of a Border Router (BR) and a Provider Edge (PE) router.
14 . The non-transitory computer-readable medium of claim 8 , wherein the reverse path SR policy further includes one or more prefix Segment Identifiers SIDs and the path includes one or more Equal Cost Multi-Paths (ECMPs), and wherein the steps further include
testing the one or more ECMPs to validate the path.
15 . A method comprising steps of:
determining a path from a router to a BGP peer, in a Segment Routing (SR) network, as a reverse path SR policy;
appending a Binding Segment Identifier (BSID) of the reverse path SR policy to a Reverse-Label-Stack attribute of a BGP update message, wherein the appending of the BSID contributes to construction of the Reverse-Label-Stack in a distributed manner as the BGP update message propagates, the construction involving each BGP speaker along the path appending a BSID of its installed reverse path SR policy; and
sending the BGP update message to the BGP peer.
16 . The method of claim 15 , wherein the steps further include
receiving a packet having, as an active segment, the BSID from the Reverse-Label Stack; and
sending the packet on the path based on the reverse path SR policy.
17 . The method of claim 16 , wherein the packet is an Operations, Administration, and Maintenance (OAM) packet including Bidirectional Forwarding Detection (BFD) or Seamless BFD (S-BFD) information, which is guaranteed to traverse a same forward and reverse path for fault detection by virtue of the co-routed reverse-path SR policy advertised in the BGP update message.
18 . The method of claim 15 , wherein the determining includes
computing a path from a BGP speaker to the BGP peer using a set of constraints for a color in a BGP color extended community.
19 . The method of claim 15 , wherein the determining includes
reversing a forward path of an SR policy which is from the BGP peer to the BGP speaker that was computed using a set of constraints for a color in a BGP color extended community.
20 . The method of claim 15 , wherein the SR network includes multiple domains, and wherein the router is one of a Border Router (BR) and a Provider Edge (PE) router.