FRR LSP switch to backup path on bypass LSP
Facility-protected FRR LSP uses a bypass LSP to carry its traffic whenever there is a failure in its protected path. Multiple events can lead to switching traffic from a protected LSP to a backup path. Some primary reasons for switching the protected LSP traffic to its corresponding backup paths over a bypass LSP include a protected or excluded interface going down, or a NHOP node going down.
At every PLR node of a facility-protected LSP, whenever a backup path is associated with a bypass LSP, the following actions take place:
- The protected LSP shows the bypass selection in its FRR details section. The protection status shows as up.
- The bypass LSP shows the backup path session information. The backup path status shows as up. The backup path role shows as Ingress if it is a protected LSP ingress PLR; otherwise, the backup path role shows as Transit.
- An Ingress Backup (BI) RSVP session is created corresponding to the backup path. There is no corresponding Merged Backup (BM) or Egress Backup (BE) RSVP session at the MP. BM and BE sessions are created upon the FRR switch.
- There are no RSVP path or reservation messages corresponding to a backup traversing over the bypass LSP before the FRR switch.
The facility-protected FRR LSP initiates the FRR switch based on the FRR switch trigger event. Upon FRR protection switch trigger, the following actions take place:
- The protected path data traffic is switched to backup path over the bypass LSP. At the PLR, switched traffic has a single backup label if the bypass LSP is a single hop and the MP is in transit. There is no label if the bypass LSP is a single hop and the MP is a protected LSP egress. There is a single bypass label if the bypass LSP is multi-hop and the MP is a protected LSP egress. There are two labels if the bypass is multi-hop and the MP is in transit.
- The backup session path message to the MP is initiated to bring up the MP node Merged Backup (BM) or Egress Backup (BE) RSVP session.
- The backup session RSVP path message is carried over the bypass LSP.
- The backup session RSVP reservation message follows any possible return path (from MP to PLR) in the network, per IP routing.
- A protected LSP shows the backup status as Active.
- A bypass LSP shows the backup status as Active.
- The bypass LSP MBB or re-optimization is not allowed until the backup status is active.
At any time, it is possible that there can be Active, switched, or up, as well as non-switched backup paths on the bypass LSP.
