Figure: Bypass Tunnel Node Example shows an example of a network used to illustrate the LSP selection rules for a PLR bypass scenario.
The PLR uses the following rules to select a bypass LSP from among multiple bypass LSPs (manually and dynamically created) when establishing the primary LSP path or when searching for a bypass for a protected LSP that does not have an association with a bypass tunnel.
The MPLS/RSVP-TE task in the PLR node checks for an existing manual bypass tunnel that satisfies the constraints. If the PATH message for the primary LSP path indicated that node protection is desired, which is the default LSP FRR setting at the head-end node, then the MPLS/RSVP-TE task searches for a node-protect bypass LSP. If the PATH message for the primary LSP path indicated that link protection is desired, then it searches for a link-protect bypass LSP.
If multiple manual bypass LSPs satisfying the path constraints exist, the PLR will prefer a manual bypass LSP terminating closer to the PLR over a manual bypass LSP terminating further away. If multiple manual bypass LSPs satisfying the path constraints terminate on the same downstream node, the PLR selects the one with the lowest IGP path cost, or if there is a tie, it picks the first one available.
If none of the manual bypass LSPs satisfy the constraints and dynamic bypass tunnels have not been disabled on the PLR node, then the MPLS/RSVP-TE task in the PLR node checks to determine if any of the already established dynamic bypass LSPs of the requested type satisfy the constraints.
If none of the dynamic bypass LSPs satisfy the constraints, then the MPLS/RSVP-TE task will ask CSPF to check if a new dynamic bypass of the requested type, node-protect or link-protect, can be established.
If the PATH message for the primary LSP path indicated node protection is desired, and no manual bypass was found after Step 1, and/or no dynamic bypass LSP was found after three attempts to perform Step 3, the MPLS/RSVP-TE task will repeat Steps 1 to 3 looking for a suitable link-protect bypass LSP. If none are found, the primary LSP will have no protection and the PLR node must clear the Local Protection Available flag in the IPv4 address sub-object of the RRO, starting in the next RESV refresh message it sends upstream.
If the PATH message for the primary LSP path indicated link protection is desired, and no manual bypass was found after Step 1, and/or no dynamic bypass LSP was found after performing Step 3, the primary LSP will have no protection and the PLR node must clear the Local Protection Available flag in the IPv4 address sub-object of the RRO, starting in the next RESV refresh message it sends upstream. The PLR will not search for a node-protect bypass LSP in this case.
If the PLR node successfully makes an association, it must set the Local Protection Available flag in the IPv4 address sub-object of the RRO, starting in the next RESV refresh message it sends upstream.
For all primary LSPs that requested FRR protection but are not currently associated with a bypass tunnel, the PLR node—upon reception of an RESV refresh message on the primary LSP path—repeats Steps 1 to 7.
If the user disables dynamic bypass tunnels on a node while dynamic bypass tunnels are activated and passing traffic, traffic loss will occur on the protected LSP. Furthermore, if no manual bypass tunnel exists that satisfies the constraints of the protected LSP, the LSP will remain without protection.
If the user configures a bypass tunnel on Node B (Figure: Bypass Tunnel Node Example) and dynamic bypass tunnels have been disabled, LSPs that had been previously signaled and that were not associated with any manual bypass tunnel (for example, none existed) will be associated with the manual bypass tunnel, if it is suitable. The node checks for the availability of a suitable bypass tunnel for each of the outstanding LSPs every time an RESV message is received for these LSPs.
If the user configures a bypass tunnel on Node B and dynamic bypass tunnels have not been disabled, LSPs that had been previously signaled over dynamic bypass tunnels will not automatically be switched to the manual bypass tunnel, even if the manual bypass tunnel is a more optimized path. The user must perform a make-before-break switchover at the head end of these LSPs. The make-before-break process is enabled using the adaptive option.
If the manual bypass tunnel goes into the down state on Node B and dynamic bypass tunnels have been disabled, Node B (PLR) will clear the ‟protection available” flag in the RRO IPv4 sub-object in the next RESV refresh message for each affected LSP. It will then try to associate each of these LSPs with one of the manual bypass tunnels that are still up. If it finds one, it will make the association and set the ‟protection available” flag in the next RESV refresh message for each of these LSPs. If it cannot find one, it will keep checking for one every time an RESV message is received for each of the remaining LSPs. When the manual bypass tunnel is back up, the LSPs that did not find a match are associated back with this tunnel and the protection available flag is set starting in the next RESV refresh message.
If the manual bypass tunnel goes into the down state on Node B and dynamic bypass tunnels have not been disabled, Node B will automatically signal a dynamic bypass tunnel to protect the LSPs if a suitable one does not exist. Similarly, if an LSP is signaled while the manual bypass tunnel is in the down state, the node will only signal a dynamic bypass tunnel if the user has not disabled dynamic tunnels. When the manual bypass tunnel is back up, the node will not switch the protected LSPs from the dynamic bypass tunnel to the manual bypass tunnel.