This document describes the use of loop-free alternates to provide local protection for unicast traffic in pure IP and MPLS/LDP networks in the event of a single failure, whether link, node, or shared risk link group (SRLG). The goal of this technology is to reduce the packet loss that happens while routers converge after a topology change due to a failure. Rapid failure repair is achieved through use of precalculated backup next-hops that are loop-free and safe to use until the distributed network convergence process completes. This simple approach does not require any support from other routers. The extent to which this goal can be met by this specification is dependent on the topology of the network.

本文档描述了在发生单一故障（无论是链路、节点还是共享风险链路组（SRLG））时，使用无环路替代方案为纯IP和MPLS/LDP网络中的单播通信提供本地保护。这项技术的目标是减少路由器在因故障而改变拓扑结构后收敛时发生的数据包丢失。快速故障修复是通过使用预先计算的备份下一跳来实现的，在分布式网络融合过程完成之前，这些备份下一跳是无环的，可以安全使用。这种简单的方法不需要其他路由器的任何支持。本规范能够满足这一目标的程度取决于网络的拓扑结构。