Nokia 7705 SAR-W Series - Dynamic and Manual Bypass Lsps; Bypass LSP Selection Rules for the PLR

MPLS and RSVP-TE
74
MPLS Guide
© 2022 Nokia.
Use subject to Terms available at: www.nokia.com
3HE 18686 AAAB TQZZA
• Administrative groups are not taken into account when creating the detour
routes for LSPs.
3.7.4 Dynamic and Manual Bypass LSPs
Users can disable dynamic bypass creation on a per-node basis using the
config>router>mpls>dynamic-bypass command. Disabling dynamic bypass
means that manual bypass is enabled. Dynamic bypass is enabled by default.
Dynamic bypass tunnels are implemented as per RFC 4090, Fast Reroute
Extensions to RSVP-TE for LSP Tunnels. When an LSP is signaled and the Local
Protection flag in the Session_attribute object is set, or the FRR object in the PATH
message indicates that facility backup is desired, the PLR establishes a bypass
tunnel to provide node and link protection. If there exists a bypass LSP that merges
with the protected LSP at a downstream node, and if this LSP satisfies the
constraints in the FRR object, then this bypass tunnel is selected and used. The
frr-object command specifies whether facility backup is signaled in the FRR object.
The manual bypass feature allows an LSP to be preconfigured from a Point of Local
Repair (PLR) that will be used exclusively for bypass protection. When a PATH
message for a new LSP requests bypass protection, the node first checks for a
manual bypass tunnel that satisfies the path constraints. If one is found, it is selected
and used. If no manual bypass tunnel is found, the 7705 SAR dynamically signals a
bypass LSP in the default behavior. To configure a manual bypass LSP, use the
bypass-only option in the config>router>mpls>lsp lsp-name [bypass-only]
command.
When a PLR activates a bypass backup LSP and subsequently receives a RESV
refresh message for the original primary LSP path reservation over the restored
interface, the PLR does not generate a ResvErr packet downstream. In addition, the
MP node, once it becomes active, does not propagate a downstream ResvErr
message received packet for the original primary LSP path reservation.
Refer to Configuring Manual Bypass Tunnels for configuration information.
3.7.4.1 Bypass LSP Selection Rules for the PLR
Figure 8 shows an example of a network used to illustrate the LSP selection rules for
a PLR bypass scenario.