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Merge pull request #18018 from forrestchu/sbfd

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doc: fix sbfd.rst doc warnings
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Donald Sharp 2025-02-05 08:17:52 -05:00 committed by GitHub
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2 changed files with 17 additions and 2 deletions
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5
doc/developer/sbfd.rst
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@ -27,7 +27,7 @@ SBFD takes the same data packet format as BFD, but with a much simpler state mac
According to RFC7880, SBFD has a stateless SBFDReflector and a stateful SBFDInitiator with the state machine as below:
::
+--+
ADMIN DOWN, | |
TIMER | V
@ -78,6 +78,7 @@ A bfd-name is always associated with a TE path, for example if we use the sbfd s
Meanwhile bfdd will notify the sbfd status to the Pathd, we should add the bfd-name field in PTM bfd notify message ZEBRA_BFD_DEST_REPLAY:
::
* Message format:
* - header: command, vrf
* - l: interface index
@ -113,6 +114,7 @@ According to RFC7881, SBFD Control packet dst port should be 7784, src port can
::
UDP(sport=4784, dport=7784)/BFD() or UDP(sport=3784, dport=7784)/BFD()
if "multihop" is specified for sbfd initiator we choose the 4784 as the source port, so the reflected packet will take 4784 as the dst port, this is a local BFD_MULTI_HOP_PORT so the reflected packet can be handled by the existing bfd_recv_cb function.
@ -122,6 +124,7 @@ if "multihop" is not specified for sbfd initiator we choose the 3784 as the sour
For echo SBFD with SRv6 encapsulation case, we re-use the BFD Echo port, the UDP ports in packet are set as:
::
UDP(sport=3785, dport=3785)/BFD()

14
doc/user/sbfd.rst
View File

@ -27,7 +27,7 @@ SBFD takes the same data packet format as BFD, but with a much simpler state mac
According to RFC7880, SBFD has a stateless SBFDReflector and a stateful SBFDInitiator with the state machine as below:
::
+--+
ADMIN DOWN, | |
TIMER | V
@ -73,24 +73,28 @@ In the following example, we set up a sbfd session to monitor the path A-B-D (al
A is the SBFDInitiator, and D is the SBFDReflector, A will trasmit the SBFD packet to B as the format:
::
IPv6(src="200::A", dst="100::B", nh=43)/IPv6ExtHdrSegmentRouting(addresses=["100::D"], nh=41, segleft=1)/IPv6(src="200::A", dst="200::D")/UDP(dport=7784)/BFD(my_dis=123, your_disc=456, state=UP)
Upon receiving the packet, B will take the Srv6 End action since the dst ip 100::B is the End address, B will the shift the dst address according to Srv6 spec, then trasmit the SBFD packet to D as the format:
::
IPv6(src="200::A", dst="100::D", nh=41)/IPv6(src="200::A", dst="200::D")/UDP(dport=7784)/BFD(my_dis=123, your_disc=456, state=UP)
After D receive the packet, It will decap the outer IPv6 header since the dst ip 100::D is the End address, the decapped packet is:
::
IPv6(src="200::A", dst="200::D")/UDP(dport=7784)/BFD(my_dis=123, your_disc=456, state=UP)
This packet will be routed to kernel stack of D since its dst is 200::D. Then the SBFDReflector service on D will get the packet and Reflect it. The response packet will be:
::
IPv6(src="200::D", dst="200::A")/UDP(sport=7784)/BFD(my_dis=456, your_disc=123, state=UP)
@ -132,18 +136,21 @@ For example, we use Echo SBFD session to protect Srv6 path: A-B-D
A is also the SBFDInitiator, and B, C, D is Srv6 ready nodes, A will trasmit the SBFD packet to B as the format:
::
IPv6(src="200::A", dst="100::B", nh=43)/IPv6ExtHdrSegmentRouting(addresses=["100::D"], nh=41, segleft=1)/IPv6(src="200::A", dst="200::A")/UDP(dport=3785)/BFD(my_dis=123, your_disc=123, state=UP)
Upon receiving the packet, B will take the Srv6 End action since the dst ip 100::B is the End address, B will the shift the dst address according to Srv6 spec, then trasmit the SBFD packet to D as the format:
::
IPv6(src="200::A", dst="100::D", nh=41)/IPv6(src="200::A", dst="200::A")/UDP(dport=3785)/BFD(my_dis=123, your_disc=123, state=UP)
After D receive the packet, It will decap the outer IPv6 header since the dst ip 100::D is the End address, the decapped packet is:
::
IPv6(src="200::A", dst="200::A")/UDP(dport=3785)/BFD(my_dis=123, your_disc=123, state=UP)
@ -181,6 +188,7 @@ We can also configure a SBFD Initiator-Reflector session based on simple IPv6/IP
A is the SBFDInitiator, and D is the SBFDReflector, A will trasmit the SBFD packet to B or C as the format:
::
IPv6(src="200::A", dst="200::D")/UDP(dport=7784)/BFD(my_dis=123, your_disc=456, state=UP)
@ -189,6 +197,7 @@ Upon receiving the packet, B/C will route the packet to D according to the dst i
After D receive the packet, packet will be sent to kernel stack of D since its dst is 200::D. Then the SBFDReflector service on D will get the packet and reflect it. The response packet will be:
::
IPv6(src="200::D", dst="200::A")/UDP(sport=7784)/BFD(my_dis=456, your_disc=123, state=UP)
@ -226,6 +235,7 @@ This command will show all the BFD and SBFD sessions in the bfdd:
::
BFD Peers:
peer 200::D bfd-mode sbfd-init bfd-name a-d multihop local-address 200::A vrf default remote-discr 456
ID: 1421669725
@ -254,6 +264,7 @@ This command will show all the BFD and SBFD session packet counters:
.. clicmd:: show bfd peers counters
::
BFD Peers:
peer 200::A bfd-mode sbfd-echo bfd-name a-b-d local-address 200::A vrf default srv6-source-ipv6 200::A srv6-encap-data 100::B 100::D
Control packet input: 0 packets
@ -281,6 +292,7 @@ we also implemented a new show command to display BFD sessions with a bfd-name,
.. clicmd:: show bfd bfd-name a-b-d
::
BFD Peers:
peer 200::A bfd-mode sbfd-echo bfd-name a-b-d local-address 200::A vrf default srv6-source-ipv6 200::A srv6-encap-data 100::B 100::D
ID: 123