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U-Turn Alternates: Cooperatively Breaking the Loop R2 can locally determine to use R1 as a U-turn alternate if and only if: R2 is the primary neighbor of R1 for any shortest paths from R1 to R4 that go through R2 (R1 is a U-turn neighbor of R2). R1 has signaled that it is capable of breaking U-turns on that interface (traffic received from R2 destined to R4 will go to R1’s alternate and not back to R2). R1 has a loop-free node-protecting alternate (R5) to reach the destination (R4). |