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U-turn Alternates for IP/LDP Fast-Reroute draft-atlas-ip-local-protect-uturn-01.txt

U-turn Alternates for IP/LDP Fast-Reroute draft-atlas-ip-local-protect-uturn-01.txt. Alia Atlas (aatlas@avici.com) Gagan Choudhury (gchoudhury@att.com) Christian Martin (cmartin@verizon.com) Brent Imhoff (brent@lightcore.net) Don Fedyk (dwfedyk@nortelnetworks.com)

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U-turn Alternates for IP/LDP Fast-Reroute draft-atlas-ip-local-protect-uturn-01.txt

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  1. U-turn Alternates for IP/LDP Fast-Reroute draft-atlas-ip-local-protect-uturn-01.txt Alia Atlas (aatlas@avici.com) Gagan Choudhury (gchoudhury@att.com) Christian Martin (cmartin@verizon.com) Brent Imhoff (brent@lightcore.net) Don Fedyk (dwfedyk@nortelnetworks.com) Raveendra Torvi (rtorvi@avici.com)

  2. Time 1 N breaks the loop and sends traffic to alternate interface 1 1 1 S E Time 2 10 Time 3 D N 2 2 R A 2 Time 4 U-Turn Alternates: Cooperatively Breaking the Loop S canlocally determine to use N as a U-turn alternate if and only if: • S is the primary neighbor of N for any shortest paths from N to D that go through S (N is a U-turn neighbor of S). • N has signaled that it is capable of breaking U-turns on that interface (U-turn traffic received from S destined to D will go to N’s alternate and not back to S). • N has a loop-free node-protecting alternate (R) to reach the destination (D). draft-atlas-ip-local-protect-loopfree-00.txt IETF-60 Routing Area WG

  3. Original Implicit Packet Identification Method • Router signals type of U-turn packet identification supported (implicit or explicitly marked) • Implicit Method • Packet is U-turn Packet if received from primary neighbor • No need to mark packets • Allows breaking of upstream micro-forwarding loops; this is best-effort because alternate computed for local failure, not a remote failure. draft-atlas-ip-local-protect-loopfree-00.txt IETF-60 Routing Area WG

  4. Added Explicitly Marked Packet Identification Method • Packet is a U-turn Packet if • Explicitly Marked (well-known label suggested) • Identifies packet as a potential U-turn packet – doesn’t imply switching. • Received from primary neighbor • This is required to handle transition cases where network isn’t converged. • Advantages • Easier to implement – marking identifies candidate U-turn packets. • Handles more broadcast link scenarios – can have neighbors in different areas (or just hosts) on same link. • Properly forwards packets from a TE LSP with Penultimate Hop Popping. • Easier to predict – Traffic gets the behavior requested. • Disadvantages • Requires an explicit marking – must be below Layer 3, b/c no bits available in IP header • Doesn’t mitigate micro-forwarding loops draft-atlas-ip-local-protect-loopfree-00.txt IETF-60 Routing Area WG

  5. Other Changes • Added example algorithm to look for U-turn alternates • Worst-case for node or link protection is 1 additional SPF per neighbor. • Connection to alternate selection clarified. • Section on SRLGs • More details needed • Clarified local hold-down considerations • Cleaned up text & terminology draft-atlas-ip-local-protect-loopfree-00.txt IETF-60 Routing Area WG

  6. What’s Next? • Simplification of Alternate Selection • Same behavior regardless of number of Potential Primary Neighbors • More Detailed Explanation Considering Link Protection • Focus on broadcast links • Link to use to access the U-turn neighbor or loop-free neighbor • Other suggestions? • What is working group interest? Please send comments to the list. draft-atlas-ip-local-protect-loopfree-00.txt IETF-60 Routing Area WG

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