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doc: add sbfd doc
Signed-off-by: wumu.zsl <wumu.zsl@alibaba-inc.com>
This commit is contained in:
wumu.zsl
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140
doc/developer/sbfd.rst
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140
doc/developer/sbfd.rst
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@ -0,0 +1,140 @@
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.. _sbfd:
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****
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SBFD
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****
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:abbr:`SBFD (Seamless Bidirectional Forwarding Detection)` is:
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Seamless Bidirectional Forwarding Detection, a simplified mechanism for using BFD with a large
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proportion of negotiation aspects eliminated, thus providing benefits
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such as quick provisioning, as well as improved control and
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flexibility for network nodes initiating path monitoring.
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-- :rfc:`7880`
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It is described and extended by the following RFCs:
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* :rfc:`7880`
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* :rfc:`7881`
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.. _sbfd-sate-machine:
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SBFD state machine
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==================
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SBFD takes the same data packet format as BFD, but with a much simpler state machine.
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According to RFC7880, SBFD has a stateless SBFDReflector and a stateful SBFDInitiator with the state machine as below:
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::
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+--+
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ADMIN DOWN, | |
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TIMER | V
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+------+ UP +------+
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| |-------------------->| |----+
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| DOWN | | UP | | UP
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| |<--------------------| |<---+
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+------+ ADMIN DOWN, +------+
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TIMER
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Figure 1: SBFDInitiator Finite State Machine
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.. _sbfd-extention:
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SBFD extension - SRv6 encapsulation
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===================================
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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,
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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,
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from the source to the destination, which could be achieved by segment routing. This requirement extends the node verification to the path verification.
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.. _sbfd-implement:
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implementation
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===============
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Some considerations when implementing sbfd.
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.. _sbfd-implement-coexist:
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SBFD Co-exist with BFD
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--------------------------
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Both SBFD and Classical BFD have their unique discriminator, SBFD can co-exist with BFD since they sharing a same discriminator pool in bfdd.
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Also in bfdd SBFD and BFD can share most code logic, SBFD packet and BFD packet are demultiplexed by different discriminators.
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.. _sbfd-implement-bfdname:
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SBFD name
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---------
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We introduced a bfd-name for every sbfd session. A unique bfd-name can be used to identify a sbfd session quickly. This is quite useful in our Srv6 deployment for path protection case.
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A bfd-name is always associated with a TE path, for example if we use the sbfd session to protect the path A-B-D, we would assign the name 'path-a-b-d' or 'a-b-d' to the session.
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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:
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::
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* Message format:
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* - header: command, vrf
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* - l: interface index
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* - c: family
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* - AF_INET:
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* - 4 bytes: ipv4
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* - AF_INET6:
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* - 16 bytes: ipv6
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* - c: prefix length
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* - l: bfd status
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* - c: family
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* - AF_INET:
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* - 4 bytes: ipv4
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* - AF_INET6:
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* - 16 bytes: ipv6
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* - c: prefix length
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* - c: cbit
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* - c: bfd name len <---- new field
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* - Xbytes: bfd name <---- new field
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*
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* Commands: ZEBRA_BFD_DEST_REPLAY
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*
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* q(64), l(32), w(16), c(8)
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.. _sbfd-implement-port:
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SBFD UDP port
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-------------
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According to RFC7881, SBFD Control packet dst port should be 7784, src port can be any but NOT 7784. In our implementation, the UDP ports in packet are set as:
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::
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UDP(sport=4784, dport=7784)/BFD() or UDP(sport=3784, dport=7784)/BFD()
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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.
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if "multihop" is not specified for sbfd initiator we choose the 3784 as the source port, this is a local BFD_DEFDESTPORT so the reflected packet can be handled by the existing bfd_recv_cb function.
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For echo SBFD with SRv6 encapsulation case, we re-use the BFD Echo port, the UDP ports in packet are set as:
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::
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UDP(sport=3785, dport=3785)/BFD()
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we choose the 3785 as the source port, so the echo back packet will take 3785 as the dst port, this is a local BFD_DEF_ECHO_PORT so the packet can be handled by the existing bfd_recv_cb function.
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.. _sbfd-not-implemented:
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Todo list for SBFD
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------------------
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Currently some features are not yet implemented for SBFD, will add it in future:
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1) SBFD in IPv4 only packet
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2) The ADMIN DOWN logic
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3) SBFD echo function in a initiator session
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4) SBFD over MPLS
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@ -82,6 +82,7 @@ dev_RSTFILES = \
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doc/developer/northbound/transactional-cli.rst \
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doc/developer/northbound/yang-module-translator.rst \
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doc/developer/northbound/yang-tools.rst \
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doc/developer/sbfd.rst \
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# end
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EXTRA_DIST += \
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304
doc/user/sbfd.rst
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304
doc/user/sbfd.rst
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@ -0,0 +1,304 @@
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.. _sbfd:
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****
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SBFD
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****
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:abbr:`SBFD (Seamless Bidirectional Forwarding Detection)` is:
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Seamless Bidirectional Forwarding Detection, a simplified mechanism for using BFD with a large
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proportion of negotiation aspects eliminated, thus providing benefits
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such as quick provisioning, as well as improved control and
|
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flexibility for network nodes initiating path monitoring.
|
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-- :rfc:`7880`
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It is described and extended by the following RFCs:
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* :rfc:`7880`
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* :rfc:`7881`
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.. _sbfd-sate-machine:
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SBFD state machine
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==================
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SBFD takes the same data packet format as BFD, but with a much simpler state machine.
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According to RFC7880, SBFD has a stateless SBFDReflector and a stateful SBFDInitiator with the state machine as below:
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::
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+--+
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ADMIN DOWN, | |
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TIMER | V
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+------+ UP +------+
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| |-------------------->| |----+
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| DOWN | | UP | | UP
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| |<--------------------| |<---+
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+------+ ADMIN DOWN, +------+
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TIMER
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Figure 1: SBFDInitiator Finite State Machine
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* If SBFDInitiator doesn't receive the response packet in time, session is DOWN.
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* If SBFDInitiator receives the response packet in time: reponse state is ADMINDOWN, session goes DOWN; reponse state is UP, session goes UP.
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.. note::
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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.
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.. _sbfd-extention:
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SBFD extension - SRv6 encapsulation
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===================================
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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,
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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,
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from the source to the destination, which could be achieved by segment routing. This requirement extends the node verification to the path verification.
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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).
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::
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+------------C-----------+
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/ \
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A---------------B---------------D
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^ ^ ^
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End: 100::A End: 100::B End: 100::D
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Loopback: 200::A Loopback: 200::D
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BFD Discrim: 123 BFD Discrim: 456
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A is the SBFDInitiator, and D is the SBFDReflector, A will trasmit the SBFD packet to B as the format:
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::
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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)
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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:
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::
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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)
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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:
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::
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IPv6(src="200::A", dst="200::D")/UDP(dport=7784)/BFD(my_dis=123, your_disc=456, state=UP)
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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:
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::
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IPv6(src="200::D", dst="200::A")/UDP(sport=7784)/BFD(my_dis=456, your_disc=123, state=UP)
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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.
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In this example, Command used to configure the SBFDInitiator on A is:
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.. 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
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Command used to configure the SBFDReflector on D is:
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.. clicmd:: sbfd reflector source-address 200::D discriminator 456
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.. _sbfd-echo:
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Echo SBFD with SRv6 encapsulation
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=================================
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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.
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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.
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For example, we use Echo SBFD session to protect Srv6 path: A-B-D
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::
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+------------C-----------+
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/ \
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A---------------B---------------D
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^ ^ ^
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End: 100::A End: 100::B End: 100::D
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Loopback: 200::A Loopback: 200::D
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BFD Discrim: 123
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A is also the SBFDInitiator, and B, C, D is Srv6 ready nodes, A will trasmit the SBFD packet to B as the format:
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::
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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)
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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:
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::
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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)
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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:
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::
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IPv6(src="200::A", dst="200::A")/UDP(dport=3785)/BFD(my_dis=123, your_disc=123, state=UP)
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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.
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In this example, Command used to configure the SBFDInitiator on A is:
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.. 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
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no configuration needed on D.
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.. _sbfd-normal:
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normal SBFD with no SRv6 encapsulation
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======================================
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We can also configure a SBFD Initiator-Reflector session based on simple IPv6/IPv4 packet, no Srv6 involved in this case.
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::
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+------------C-----------+
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/ \
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A---------------B---------------D
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^ ^ ^
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Loopback: 200::A Loopback: 200::D
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BFD Discrim: 123 BFD Discrim: 456
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A is the SBFDInitiator, and D is the SBFDReflector, A will trasmit the SBFD packet to B or C as the format:
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::
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IPv6(src="200::A", dst="200::D")/UDP(dport=7784)/BFD(my_dis=123, your_disc=456, state=UP)
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Upon receiving the packet, B/C will route the packet to D according to the dst ip 200::D.
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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:
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::
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IPv6(src="200::D", dst="200::A")/UDP(sport=7784)/BFD(my_dis=456, your_disc=123, state=UP)
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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.
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In this example, Command used to configure the SBFDInitiator on A is:
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.. clicmd:: peer 200::D bfd-mode sbfd-init bfd-name a-d local-address 200::A remote-discr 456
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Command used to configure the SBFDReflector on D is:
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.. clicmd:: sbfd reflector source-address 200::D discriminator 456
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.. note::
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Currently some features are not yet implemented:
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1) SBFD in IPv4 only packet
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2) The ADMIN DOWN logic
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3) SBFD echo function in a initiator session
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4) SBFD over MPLS
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.. _sbfd-show:
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show command
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============
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The exsiting bfd show command is also appliable to SBFD sessions, for example:
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This command will show all the BFD and SBFD sessions in the bfdd:
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.. clicmd:: show bfd peers
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::
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BFD Peers:
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peer 200::D bfd-mode sbfd-init bfd-name a-d multihop local-address 200::A vrf default remote-discr 456
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ID: 1421669725
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Remote ID: 456
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Active mode
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Minimum TTL: 254
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Status: up
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Uptime: 5 hour(s), 48 minute(s), 39 second(s)
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Diagnostics: ok
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Remote diagnostics: ok
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Peer Type: sbfd initiator
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Local timers:
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Detect-multiplier: 3
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Receive interval: 300ms
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Transmission interval: 1000ms
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Echo receive interval: 50ms
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Echo transmission interval: disabled
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Remote timers:
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Detect-multiplier: -
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Receive interval: -
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Transmission interval: -
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Echo receive interval: -
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This command will show all the BFD and SBFD session packet counters:
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.. clicmd:: show bfd peers counters
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::
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BFD Peers:
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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
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Control packet input: 0 packets
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Control packet output: 0 packets
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Echo packet input: 23807 packets
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Echo packet output: 23807 packets
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Session up events: 1
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Session down events: 0
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Zebra notifications: 1
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Tx fail packet: 0
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peer 200::D bfd-mode sbfd-init bfd-name a-d local-address 200::A vrf default remote-discr 456
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Control packet input: 25289 packets
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Control packet output: 51812 packets
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Echo packet input: 0 packets
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Echo packet output: 0 packets
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Session up events: 5
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Session down events: 4
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Zebra notifications: 9
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Tx fail packet: 0
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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.
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.. clicmd:: show bfd bfd-name a-b-d
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::
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BFD Peers:
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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
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ID: 123
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Remote ID: 123
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Active mode
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Status: up
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Uptime: 5 hour(s), 39 minute(s), 34 second(s)
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Diagnostics: ok
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Remote diagnostics: ok
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Peer Type: echo
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Local timers:
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Detect-multiplier: 3
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Receive interval: 300ms
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Transmission interval: 300ms
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Echo receive interval: 300ms
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Echo transmission interval: 1000ms
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Remote timers:
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Detect-multiplier: -
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Receive interval: -
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Transmission interval: -
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Echo receive interval: -
|
||||
@ -55,6 +55,7 @@ user_RSTFILES = \
|
||||
doc/user/watchfrr.rst \
|
||||
doc/user/wecmp_linkbw.rst \
|
||||
doc/user/mgmtd.rst \
|
||||
doc/user/sbfd.rst \
|
||||
# end
|
||||
|
||||
EXTRA_DIST += \
|
||||
|
||||
Loading…
Reference in New Issue
Block a user