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Configuration Guide - IP Unicast Routing

CloudEngine 12800 and 12800E V200R002C50

This document describes the configurations of IP Unicast Routing, including IP Routing, Static Route, RIP, RIPng, OSPF, OSPFv3, IPv4 IS-IS, IPv6 IS-IS, BGP, Routing Policy, and PBR.

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BGP Auto Fast Reroute (FRR) is a protection measure against link failures. It applies to the network topology with primary and backup links and provides sub-second-level switching between two BGP peers or two next hops.

After BGP Auto FRR is enabled on a device, the device selects the optimal route from the routes that carry the same prefix and are learned from multiple peers as the primary link to forward packets, and uses the second optimal route as the backup link. When the primary link becomes faulty, the system rapidly responds to the notification that the BGP route becomes unreachable, and then switches traffic from the primary link to the backup link. After BGP convergence is complete, BGP Auto FRR uses the optimal route selected by BGP to guide traffic forwarding. For details about Auto FRR, see "Auto FRR" in Feature Description - IP Routing.

Application Scenarios

As shown in Figure 9-11, RouterD advertises a learned BGP route to RouterB and RouterC in AS 100; RouterB and RouterC then advertise the BGP route to RouterA through a route reflector. RouterA receives two routes whose next hops are RouterB and RouterC respectively. Then RouterA selects a route according to the configured policy. Assume that the route sent from RouterB, namely LinkB, is preferred. The route sent from RouterC, namely LinkC, then functions as the backup link.

Figure 9-11 Networking diagram of BGP Auto FRR

When a router along LinkB fails or faults occur on LinkB, the next hop of the route from RouterA to RouterB becomes invalid. If BGP Auto FRR is enabled on RouterA, the forwarding plane quickly switches traffic sent from RouterA to RouterD to LinkC. This prevents traffic loss. In addition, RouterA reselects the route sent from RouterC and updates the FIB table.

Updated: 2019-03-21

Document ID: EDOC1000166601

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