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diff --git a/doc/user/sbfd.rst b/doc/user/sbfd.rst new file mode 100644 index 0000000000..390d82a6c0 --- /dev/null +++ b/doc/user/sbfd.rst @@ -0,0 +1,304 @@ +.. _sbfd: + +**** +SBFD +**** + +:abbr:`SBFD (Seamless Bidirectional Forwarding Detection)` is: + + Seamless Bidirectional Forwarding Detection, a simplified mechanism for using BFD with a large + proportion of negotiation aspects eliminated, thus providing benefits + such as quick provisioning, as well as improved control and + flexibility for network nodes initiating path monitoring. + + -- :rfc:`7880` + +It is described and extended by the following RFCs: + +* :rfc:`7880` +* :rfc:`7881` + +.. _sbfd-sate-machine: + +SBFD state machine +================== + +SBFD takes the same data packet format as BFD, but with a much simpler state machine. +According to RFC7880, SBFD has a stateless SBFDReflector and a stateful SBFDInitiator with the state machine as below: + +:: + + +--+ + ADMIN DOWN, | | + TIMER | V + +------+ UP +------+ + | |-------------------->| |----+ + | DOWN | | UP | | UP + | |<--------------------| |<---+ + +------+ ADMIN DOWN, +------+ + TIMER + + Figure 1: SBFDInitiator Finite State Machine + +* If SBFDInitiator doesn't receive the response packet in time, session is DOWN. +* If SBFDInitiator receives the response packet in time: reponse state is ADMINDOWN, session goes DOWN; reponse state is UP, session goes UP. + +.. note:: + + SBFDReflector is stateless, it just transmit a packet in response to a received S-BFD packet having a valid S-BFD Discriminator in the Your Discriminator field. + + +.. _sbfd-extention: + +SBFD extension - SRv6 encapsulation +=================================== + +SBFDInitiator periodically send packets to monitor the connection to SBFDReflector. We set up an SBFD connection between the source and the destination node of a path, +with the source node serving as Initiator and the destination node as Reflector. The communicated SBFD packets should also follow every exact hop in the path, +from the source to the destination, which could be achieved by segment routing. This requirement extends the node verification to the path verification. +In the following example, we set up a sbfd session to monitor the path A-B-D (all nodes in the topo are SRv6 ready, which can decap and forward SRv6 packets). + +:: + + +------------C-----------+ + / \ + A---------------B---------------D + ^ ^ ^ + | | | + End: 100::A End: 100::B End: 100::D + Loopback: 200::A Loopback: 200::D + BFD Discrim: 123 BFD Discrim: 456 + + +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) + + +This packet will be routed in the topo according to the dst ip 200::A, it will go back to A by D-B-A or D-C-A in this case. + + + + In this example, Command used to configure the SBFDInitiator on A is: + +.. clicmd:: peer 200::D bfd-mode sbfd-init bfd-name a-b-d multihop local-address 200::A remote-discr 456 srv6-source-ipv6 200::A srv6-encap-data 100::B 100::D + + + Command used to configure the SBFDReflector on D is: + +.. clicmd:: sbfd reflector source-address 200::D discriminator 456 + + +.. _sbfd-echo: + +Echo SBFD with SRv6 encapsulation +================================= + +The SBFD Initiator-Reflector mode requires the configuration on both source and destination nodes. It can not work if the remote node has no SBD feature supported, especial on some third-party devices. +The Echo SBFD can solve this kind of deployment issue since it only requires the configuration on source node. This is also known as One-Arm BFD Echo or unaffiliated BFD Echo. +For example, we use Echo SBFD session to protect Srv6 path: A-B-D + +:: + + +------------C-----------+ + / \ + A---------------B---------------D + ^ ^ ^ + | | | + End: 100::A End: 100::B End: 100::D + Loopback: 200::A Loopback: 200::D + BFD Discrim: 123 + + +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) + + +This packet will be routed in the topo according to the dst ip 200::A, it will go back to A by D-B-A or D-C-A in this case. + + + + In this example, Command used to configure the SBFDInitiator on A is: + +.. clicmd:: peer 200::A bfd-mode sbfd-echo bfd-name a-b-d local-address 200::A srv6-source-ipv6 200::A srv6-encap-data 100::B 100::D + + + no configuration needed on D. + + +.. _sbfd-normal: + +normal SBFD with no SRv6 encapsulation +====================================== + +We can also configure a SBFD Initiator-Reflector session based on simple IPv6/IPv4 packet, no Srv6 involved in this case. + +:: + + +------------C-----------+ + / \ + A---------------B---------------D + ^ ^ ^ + | | | + Loopback: 200::A Loopback: 200::D + BFD Discrim: 123 BFD Discrim: 456 + + + +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) + + +Upon receiving the packet, B/C will route the packet to D according to the dst ip 200::D. + +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) + + +This packet will be routed in the topo according to the dst ip 200::A, it will go back to A by D-B-A or D-C-A in this case. + + + In this example, Command used to configure the SBFDInitiator on A is: + +.. clicmd:: peer 200::D bfd-mode sbfd-init bfd-name a-d local-address 200::A remote-discr 456 + + + Command used to configure the SBFDReflector on D is: + +.. clicmd:: sbfd reflector source-address 200::D discriminator 456 + + +.. note:: + + Currently some features are not yet implemented: + 1) SBFD in IPv4 only packet + 2) The ADMIN DOWN logic + 3) SBFD echo function in a initiator session + 4) SBFD over MPLS + + +.. _sbfd-show: + +show command +============ + +The exsiting bfd show command is also appliable to SBFD sessions, for example: +This command will show all the BFD and SBFD sessions in the bfdd: + +.. clicmd:: show bfd peers + + +:: + 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 + Remote ID: 456 + Active mode + Minimum TTL: 254 + Status: up + Uptime: 5 hour(s), 48 minute(s), 39 second(s) + Diagnostics: ok + Remote diagnostics: ok + Peer Type: sbfd initiator + Local timers: + Detect-multiplier: 3 + Receive interval: 300ms + Transmission interval: 1000ms + Echo receive interval: 50ms + Echo transmission interval: disabled + Remote timers: + Detect-multiplier: - + Receive interval: - + Transmission interval: - + Echo receive interval: - + +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 + Control packet output: 0 packets + Echo packet input: 23807 packets + Echo packet output: 23807 packets + Session up events: 1 + Session down events: 0 + Zebra notifications: 1 + Tx fail packet: 0 + + peer 200::D bfd-mode sbfd-init bfd-name a-d local-address 200::A vrf default remote-discr 456 + Control packet input: 25289 packets + Control packet output: 51812 packets + Echo packet input: 0 packets + Echo packet output: 0 packets + Session up events: 5 + Session down events: 4 + Zebra notifications: 9 + Tx fail packet: 0 + + +we also implemented a new show command to display BFD sessions with a bfd-name, the bfd-name is the key to search the sessioon. + +.. 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 + Remote ID: 123 + Active mode + Status: up + Uptime: 5 hour(s), 39 minute(s), 34 second(s) + Diagnostics: ok + Remote diagnostics: ok + Peer Type: echo + Local timers: + Detect-multiplier: 3 + Receive interval: 300ms + Transmission interval: 300ms + Echo receive interval: 300ms + Echo transmission interval: 1000ms + Remote timers: + Detect-multiplier: - + Receive interval: - + Transmission interval: - + Echo receive interval: - |