Alcatel-Lucent 7450 Manual page 118

Diff-Serv TE LSP Class Type Change under Failure
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Page 118
When a LSP primary path retries due a failure, for example, it fails after being in the up
state, or undergoes any type of MBB, MPLS will retry a new path for the LSP using the
main CT. If the first attempt failed, the head-end node performs subsequent retries using
the backup CT. This procedure must be followed regardless if the currently used CT by
this path is the main or backup CT. This applies to both CSPF and non-CSPF LSPs.
The triggers for using the backup CT after the first retry attempt are:
→ A local interface failure or a control plane failure (hello timeout, etc.).
→ Receipt of a PathErr message with a notification of a FRR protection becoming active
downstream and/or receipt of a Resv message with a 'Local-Protection-In-Use' flag
set. This invokes the FRR Global Revertive MBB.
→ Receipt of a PathErr message with error code=25 (Notify) and sub-code=7 (Local link
maintenance required) or a sub-code=8 (Local node maintenance required). This
invokes the TE Graceful Shutdown MBB. Note that in this case, only a single attempt
is performed by MBB as in current implementation; only the main CT will be retried.
→ Receipt of a Resv refresh message with the 'Preemption pending' flag set or a PathErr
message with error code=34 (Reroute) and a value=1 (Reroute request soft
preemption). This invokes the soft pre-emption MBB.
→ Receipt of a ResvTear message.
→ A configuration change MBB.
When an unmapped LSP primary path goes into retry, it uses the main CT until the
number of retries reaches the value of the new main-ct-retry-limit parameter. If the path
did not come up, it must start using the backup CT at that point in time. By default, this
parameter is set to infinite value. The new main-ct-retry-limit parameter has no effect on
an LSP primary path, which retries due to a failure event. This parameter is configured
using the main-ct-retry-limit command in the config>router>mpls>lsp context. If the
user entered a value of the main-ct-retry-limit parameter that is greater than the LSP
retry-limit, the number of retries will still stop when the LSP primary path reaches the
value of the LSP retry-limit. In other words, the meaning of the LSP retry-limit parameter
is not changed and always represents the upper bound on the number of retries. The
unmapped LSP primary path behavior applies to both CSPF and non-CSPF LSPs.
An unmapped LSP primary path is a path that never received a Resv in response to the
first path message sent. This can occur when performing a "shut/no-shut" on the LSP or
LSP primary path or when the node reboots. An unmapped LSP primary path goes into
retry if the retry timer expired or the head-end node received a PathErr message before the
retry timer expired.
When the clear>router>mpls>lsp command is executed, the retry behavior for this LSP
is the same as in the case of an unmapped LSP.
If the value of the parameter main-ct-retry-limit is changed, the new value will only be
used at the next time the LSP path is put into a "no-shut" state.
The following is the behavior when the user changes the main or backup CT:
7450 ESS MPLS Guide