Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 977)

Multi-Service IronWare Switching Configuration Guide 947
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Configuring BFD for RSVP-TE LSPs
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BFD for RSVP-TE LSPs operates with Fast ReRoute (FRR), Redundant, and Adaptive LSPs as
described:
• FRR LSPs – Only one BFD session is created for an FRR LSP. A separate BFD session is not
created for the detour path. When a switchover from a protected to a detour path occurs, the
detour path resides on another interface module, and the BFD session is moved to that
interface module. The BFD session can go down if the interface module has already reached
the maximum number of BFD sessions. If the detour path is on the same interface module, the
outgoing interface and label stack are updated on that interface module. A BFD session is not
created for a detour path originated on a transit LSR.
• Redundant LSPs – One BFD session is created for the primary path of a redundant LSP. If the
secondary path is in the hot-standby condition, a separate BFD session is created for it, but
only if BFD is enabled on the secondary path. The two sessions operate independently.
• Adaptive LSPs – If a new instance of an adaptive LSP comes up on a different interface
module, its BFD session is automatically created on that module. Otherwise, the local outgoing
interface and label stack are updated on the existing interface module. When a BFD session is
moved to a different interface module, the BFD session may be brought down if the interface
module has already reached the maximum number of BFD sessions allowed on it.
BFD session support per-router and per-interface module
There is a limit to the number of BFD sessions available on a per-router and per-interface module
basis as described:
• per-router – A maximum number of 250 BFD sessions are permitted per device
• per-interface module – A maximum number of 80 BFD sessions (Tx or Rx) are permitted
per-interface module
These limitations are inclusive of any BFD sessions created for OSPFv2 or v3 and IS-IS. If creating a
BFD session will exceed these limits, the session will be denied. For a detailed description of how to
calculate the number of BFD sessions supported, refer to
“Number of BFD sessions supported” .
BFD session creation
On ingress, one BFD session is created for each LSP after the LSP comes up. The BFD session
status is then displayed in the output of the show lsp command. If the BFD session is not up, a
failure reason is displayed in the output of the show lsp command. Possible reasons why a BFD
session may fail to come up include exceeding the maximum supported number of BFD sessions,
or if the global BFD configuration is disabled. If a BFD session does not come up because a BFD
packet from the egress LSR is not received, an MPLS Echo Request with a BFD Discriminator TLV is
resent until the session does come up. The retry timer is exponentially backed off.
On egress, a BFD session is created after the following sequence of events.
1. An MPLS Echo Request is received with a BFD Discriminator TLV
2. MPLS BFD is enabled globally
3. The maximum number of BFD sessions available on the device has not been reached.
NOTE
A BFD session created on an egress LSR is counted toward the maximum supported number of
BFD sessions.