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 CRLSP, and 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 CRLSP—Used to protect the primary CRLSP.
Point of local repair—A PLR is the ingress node of the bypass CRLSP. 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 CRLSP. 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 CRLSP. As shown in Figure 20, the primary CRLSP is Router A—Router B—Router C—Router D, and the bypass CRLSP is Router B—Router F—Router C.
Figure 20: 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 CRLSP. As shown in Figure 21, the primary CRLSP is Router A—Router B—Router C—Router D—Router E, and the bypass CRLSP is Router B—Router F—Router D. Router C is the protected device.
Figure 21: FRR node protection
FRR deployment
Following these guidelines to deploy FRR:
Make sure the protected link or node is not on the bypass CRLSP.
FRR requires extra bandwidth because bypass CRLSPs must be pre-established. When network bandwidth is insufficient, use FRR only for crucial nodes or links.