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DES-7200 Configuration Guide Chapter 3 MPLS Reliability Configuration
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(generated by Egress LSR) to the Ingress LSR. This process is the same for Egress LSR,
and we will not give unnecessary details herein. It shall be noted when no discriminator is
defined at both ends, your discriminator must be learned through the LSP Ping echo packet.
If both ends have defined my discriminator and your discriminator, then this step will be
neglected during the process of establishing BFD session. Please refer to the section of
"BFD for LSP" for discriminator configuration.
z Ingress LSR and Egress LSR initiate BFD, with initial state being "Down" and the BFD
packet sent carrying "Down" state.
z Egress LSR receives the BFD packet with state being "Down". The local BFD switches state
to "Init" and sends BFD packet carrying "Init" state.
z After Egress LSR switches local BFD state to "Init", it will no longer process BFD packets
with state being "Down".
z The BFD state changing process of Ingress LSR is the same as above.
z Egress LSR receives the BFD packet with state being "Init". The local BFD switches state to
"Up".
z The BFD state changing process of Ingress LSR is the same as above.
z Local BFD state changes to "Up", indicating that the BFD session is established
successfully.
Detection mode
Before exchanging BFD control packets between two devices, a BFD session must be
established, and the control plane and data plane must share the same path. There are two BFD
operating modes:
z Asynchronous mode
z Demand mode
Besides these two modes, Echo feature is also defined in BFD. It can be applied in both
asynchronous mode and demand mode.
Currently, BFD for LSP can only support asynchronous mode. It cannot support demand mode
or Echo mode.