Nokia 7705 SAR-W Series - Service and Shortcut Application SR-TE Label Stack Check; Table 7 Parameter Values for Frr-Overhead

MPLS and RSVP-TE
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MPLS Guide
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3.12.3.1 Service and Shortcut Application SR-TE Label Stack Check
Each service and shortcut application on the router performs a check of the resulting
net label stack after pushing all the labels required for forwarding the packet in that
context. The MPLS module populates each SR-TE LSP in the TTM with the
maximum transport label stack size, which consists of the sum of the values in
max-sr-labels label-stack-size and additional-frr-labels labels.
Each service or shortcut application then adds the additional, context-specific labels,
such as service label and NGE label, required to forward the packet in that context,
and checks that the resulting net label stack size does not exceed the maximum label
stack supported by the router.
If the check succeeds, the service is bound or the prefix is resolved to the SR-TE
LSP. If the check fails, the service will not bind to this SR-TE LSP. Instead, the
service will either find another SR-TE LSP or another tunnel of a different type to bind
to, if the user configured the use of other tunnel types. Otherwise, the service will go
down.
When the service uses an SDP with one or more SR-TE LSPs (up to eight), the
spoke SDP bound to this SDP will remain operationally down as long as at least one
SR-TE LSP fails the check. In this case, the spoke SDP flag
“labelStackLimitExceeded” will be displayed in the show output of the service. As
well, the prefix will not get resolved to the SR-TE LSP and will either be resolved to
another SR-TE LSP or another tunnel type or become unresolved.
The value of additional-frr-labels labels is checked against the maximum value
across all IGP instances of the parameter frr-overhead. The frr-overhead parameter
value is computed within an IGP instance as shown in Table 7. For more information
on FRR overhead, refer to the “Segment Routing in Shortest Path Forwarding”
section in the 7705 SAR Routing Protocols Guide.
Table 7 Parameter Values for frr-overhead
Condition Parameter Value
segment-routing is disabled in the IGP instance 0
segment-routing is enabled but remote-lfa is disabled
and ti-lfa is disabled
0
segment-routing is enabled and remote-lfa is enabled
but ti-lfa is disabled
1
segment-routing is enabled and ti-lfa is enabled,
regardless of whether remote-lfa is enabled or disabled
ti-lfa max-sr-frr-labels
label