FRR
Fast reroute (FRR) protects CRLSPs from link and node failures. FRR can implement 50-millisecond CRLSP failover.
After FRR is enabled for an MPLS TE tunnel, once a link or node fails on the primary CRLSP, FRR reroutes the traffic to a bypass tunnel. The ingress node attempts to set up a new CRLSP. After the new CRLSP is set up, traffic is forwarded on the new CRLSP.
CRLSP backup provides end-to-end path protection for a CRLSP without time limitation. FRR provides quick but temporary protection for a link or node on a CRLSP.
Basic concepts
Primary CRLSP—Protected CRLSP.
Bypass tunnel—An MPLS TE tunnel used to protect a link or node of the primary CRLSP.
Point of local repair—A PLR is the ingress node of the bypass tunnel. It must be located on the primary CRLSP but must not be the egress node of the primary CRLSP.
Merge point—An MP is the egress node of the bypass tunnel. It must be located on the primary CRLSP but must not be the ingress node of the primary CRLSP.
Protection modes
FRR provides the following protection modes:
Link protection—The PLR and the MP are connected through a direct link and the primary CRLSP traverses this link. When the link fails, traffic is switched to the bypass tunnel. As shown in Figure 25, the primary CRLSP is Router A—Router B—Router C—Router D, and the bypass tunnel is Router B—Router F—Router C. This mode is also called next-hop (NHOP) protection.
Figure 25: FRR link protection
Node protection—The PLR and the MP are connected through a device and the primary CRLSP traverses this device. When the device fails, traffic is switched to the bypass tunnel. As shown in Figure 26, the primary CRLSP is Router A—Router B—Router C—Router D—Router E, and the bypass tunnel is Router B—Router F—Router D. Router C is the protected device. This mode is also called next-next-hop (NNHOP) protection.
Figure 26: FRR node protection
