Alcatel-Lucent 7450 Manual page 278

MPLS Commands
If CSPF is not enabled on the LSP name, then a secondary path of that LSP which has the SRLG
constraint included will be shut down and a specific failure code will indicate the exact reason for the
failure in show>router>mpls>lsp>path>detail output.
At initial primary LSP path establishment, if primary does not come up or primary is not configured,
SRLG secondary will not be signaled and will put to down state. A specific failure code will indicate
the exact reason for the failure in show>router>mpls>lsp>path>detail output. However, if a non-
SRLG secondary path was configured, such as a secondary path with the SRLG option disabled,
MPLS/RSVP task will signal it and the LSP use it.
As soon as the primary path is configured and successfully established, MPLS/RSVP moves the LSP
to the primary and signals all SRLG secondary paths.
Any time the primary path is re-optimized, has undergone MBB, or has come back up after being
down, MPLS/RSVP task checks with CSPF if the SRLG secondary should be re-signaled. If MPLS/
RSVP finds that current secondary path is no longer SRLG disjoint, for example, it became
ineligible, it puts it on a delayed MBB immediately after the expiry of the retry timer. If MBB fails at
the first try, the secondary path is torn down and the path is put on retry.
At the next opportunity the primary goes down, the LSP will use the path of an eligible SRLG
secondary if it is UP. If all secondary eligible SLRG paths are Down, MPLS/RSVP will use a non
SRLG secondary if configured and UP. If while the LSP is using a non SRLG secondary, an eligible
SRLG secondary came back up, MPLS/RSVP will not switch the path of the LSP to it. As soon as
primary is re-signaled and comes up with a new SLRG list, MPLS/RSVP will re-signal the secondary
using the new SRLG list.
A secondary path which becomes ineligible as a result of an update to the SRLG membership list of
the primary path will have the ineligibility status removed on any of the following events:
Once primary path of the LSP is setup and is operationally up, any subsequent changes to the SRLG
group membership of an interface the primary path is using would not be considered until the next
opportunity the primary path is re-signaled. The primary path may be re-signaled due to a failure or
to a make-before-break operation. Make-before-break occurs as a result of a global revertive
operation, a timer based or manual re-optimization of the LSP path, or an operator change to any of
the path constraints.
One an SRLG secondary path is setup and is operationally UP, any subsequent changes to the SRLG
group membership of an interface the secondary path is using would not be considered until the next
opportunity secondary path is re-signaled. The secondary path is re-signaled due to a failure, to a re-
signaling of the primary path, or to a make before break operation. Make-before break occurs as a
result of a timer based or manual re-optimization of the secondary path, or an operator change to any
of the path constraints of the secondary path, including enabling or disabling the SRLG constraint
itself.
Also, the user-configured include/exclude admin group statements for this secondary path are also
checked together with the SRLG constraints by CSPF. Finally, note that enabling SRPG on a
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1. A successful MBB of the standby SRLG path which makes it eligible again.
1. The standby path goes down. MPLS/RSVP puts the standby on retry at the expiry of the retry
timer. If successful, it becomes eligible. If not successful after the retry-timer expired or the
number of retries reached the number configured under the retry-limit parameter, it is left
down.
1. The primary path goes down. In this case, the ineligible secondary path is immediately torn
down and will only be re-signaled when the primary comes back up with a new SRLG list.
7450 ESS MPLS Guide