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Alia Atlas (aatlas@avici) Gagan Choudhury (gchoudhury@att)

Basic Specification for IP Fast-Reroute: Loop-Free Alternates draft-ietf-rtgwg-ipfrr-spec-base-03.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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Alia Atlas (aatlas@avici) Gagan Choudhury (gchoudhury@att)

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  1. Basic Specification for IP Fast-Reroute: Loop-Free Alternates draft-ietf-rtgwg-ipfrr-spec-base-03.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. Changes to Draft • Added section on multi-homed prefixes & removed inheritance section for multi-region. • Added more details on SRLGs & looping scenarios possible when alternate protection isn’t sufficient for occurred failure. • Added section on ECMP & that protection is only potentially provided. • Text clean-up (thanks Alex) – but more is still needed. • Describes OSPF issue (more details) and defines Strict Downstream Alternates. draft-ietf-rtgwg-ipfrr-spec-base-03.txt IETF-62 Routing Area WG

  3. OSPF Multi-Area Issues • In OSPF, an ABR may decide between two routes from different areas based upon the cost. This can cause traffic sent to an LFA to loop back to S by exiting the area and re-entering the same area elsewhere. draft-ietf-rtgwg-ipfrr-spec-base-03.txt IETF-62 Routing Area WG

  4. OSPF Problem Scenarios • Virtual Links – Can decide to send traffic to a different router than indicated by the backbone topology. Traffic path traversed is not known based on backbone SPT. • Alternate ABRs – If inter-area routes are learned from multiple areas, then traffic path may exit and re-enter area. • Multi-area ASBRs – If an ASBR announces its location into multiple non-backbone areas, then other ABRs also in two or more of those non-backbone areas can cost-based decision between intra-area paths from different areas. • AS ExternalRoutes – If same route is advertised with same type metric from forwarding addresses (or ASBRs) in different non-backbone areas connected by at least one ABR, then that ABR has decision between intra-area paths from different areas. draft-ietf-rtgwg-ipfrr-spec-base-03.txt IETF-62 Routing Area WG

  5. Applicability Statement Proposed • Virtual Links not supported. • Alternate ABRs not supported. • If ASBR is in multiple non-backbone areas, then no other ABR is also in more than one of those non-backbone areas. • AS External Route of specific type (1 or 2) must not be announced with a forwarding addresses from multiple non-backbone areas IF those non-backbone areas share at least one ABR. draft-ietf-rtgwg-ipfrr-spec-base-03.txt IETF-62 Routing Area WG

  6. Strict Downstream Alternates • It is possible to provide link and node protection even in inapplicable scenarios – by requiring that the alternate is strictly closer to the destination than S, the link or the node being protecting. • Substantially limits coverage – more restrictive than downstream paths. • Cannot provide SRLG protection b/c SRLG protection is path based not distance based, and the path taken is unknown. • May be useful for problems scenarios? Opinions? draft-ietf-rtgwg-ipfrr-spec-base-03.txt IETF-62 Routing Area WG

  7. Future Draft Changes • Add OSPF Applicability Statement as described. • If Strict Downstream Alternates are considered useful/necessary to handle other cases, then describe them more clearly & separately. Otherwise, remove them. • Text Clean-up • Other? Please send comments to the list. draft-ietf-rtgwg-ipfrr-spec-base-03.txt IETF-62 Routing Area WG

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