Inter-area MPLS TE Architecture and Protocol Extensions draft-venkatachalam-interarea-mpls-te-01.txt draft-dharanikota-interarea-mpls-te-ext-01.txt Senthil Venkatachalam - Alcatel USA Sudheer Dharanikota - Nayna Networks Inc. © Senthil Venkatachalam and Sudheer Dharanikota, December 2000. All rights reserved.

Senthil, Sudheer, Thomas Outline Introduction to the problem Our solution Routing component Signaling component Configuration component Conclusions What next? December 12, 2000 Senthil, Sudheer, Thomas

Introduction to the Problem Why is inter-area LSP setup not attempted till now? Routing: TE metric values are defined and propagated for intra-area only Interface-level TE metrics need to be extended and propagated to networks. Signaling: No effective way to signal routing constraints across areas Also no specific mechanisms available for requesting a group of constraints. What is needed in a solution? Known TE LSP setup methods with backward compatibility Known routing mechanisms for backward compatibility Scalability Possible solutions for inter-area LSP setup LSP stitching => manual config. (not suitable for on-demand services) Offline computation (Single point-of-failure and NRT) On-line TE compute server (Additional HW and new paradigm) Manual - Tedious? Random+Crankback - Expensive? Offline - Slow/n-RT TE Compute Servers - not scalable, additional hardware December 12, 2000 Senthil, Sudheer, Thomas

Introduction to the Problem What is the problem? Past: Complete topology information is not propagated across the area. Intention: Reduce the IGP routing table size. Problem: Sub-optimal paths are taken by the SPF based routers. Solution: Summary routes across areas. Assumption: Number of such routes would be less. Current: Path attributes are not propagated across an area. Problems: Path computation: Sub-optimal paths chosen by CSPF based routers across areas. Crankback: Crankback to the source or to an arbitrary ABR! Solution: Limited summarization of TE information across areas. Current: Single constraint problem. The need for more than one constraint to calculate an end-to-end path. Alternative constraints can be specified to reduce the crankback and hence the set up time. due to unavailability of resources and unavailability of the most recent information. Solution: Group the constraints (called criteria) and give an alternative. Manual - Tedious? Random+Crankback - Expensive? Offline - Slow/n-RT TE Compute Servers - not scalable, additional hardware December 12, 2000 Senthil, Sudheer, Thomas

Senthil, Sudheer, Thomas Our solution Criteria ~ is a “group of constraints to be applied for a path computation” A primary and secondary criteria are defined for a path Routing protocols Extended to advertise TE information across areas (Opaque TE summary LSA) Extended CSPF for inter area Signaling protocols Extended to carry primary and secondary criteria Extended to carry new error conditions Area 0 Area 1 Area 2 LSP Section 1 LSP Section 2 LSP Section 3 December 12, 2000 Senthil, Sudheer, Thomas

Senthil, Sudheer, Thomas Routing Component Extension of IGPs for Inter-area TE attribute summarization ~ is the TE equivalent of IGP metric summarization Summarized TE metrics For OSPF: [draft-venkatachalam-ospf-traffic-00.txt] Opaque (Area scope) LSA - advertised into neighboring areas For ISIS [draft-dharanikota-interarea-mpls-te-ext-01.txt] New TLVs defined for summarized TE metrics and advertised into other areas Extensions to CSPF: At head node of each LSP section (LER or ABR): Use the TE-summary-LSAs (if available) to determine, a priori: Whether the constraints on the inter-area LSP can be met, and if so, The ABR that is “closest” to the destination in terms of the given constraints Determine an intra-area route (CSPF) to the chosen ABR December 12, 2000 Senthil, Sudheer, Thomas

Routing: Additive TE Metric Summarization Additive metric Use simple Dijkstra algorithm to compute summary E.g.: ospf-metric, TE-metric, delay Area 2 R1 Area 1 R3 10 10 R4 R2 N4 5 Summary For N4 Delay = 15 ms R5 5 R6 5 December 12, 2000 Senthil, Sudheer, Thomas

Routing: Max-Min TE Metric Summarization Max-Min metric Use a modified Dijkstra algorithm to summarize Summarized metric value = Max over all path costs, where Path cost = Min of component link costs E.g.: Unreserved bandwidth in CT1, CT2, max. reservable bandwidth 3 5 4 Area 1 R2 R3 R6 R4 R5 Area 2 R1 7 Summary For N4 Unreserved BW in CT1 = 4 Mbps N4 December 12, 2000 Senthil, Sudheer, Thomas

Routing: Other TE Metric Summarization Other metrics: use a modified Dijkstra algorithm to summarize Summarized metric value = F (over all path costs), where Path cost = G (over all component links of that path) Functions F,G: configurable! E.g.: resource class/colors, SRLG. Example for bit-mapped colors can be: F = OR, G = AND Summary For N4 Color Supported = 0x93 0xFF 0x13 0xb3 0x95 Area 1 R2 R3 R6 R4 R5 Area 2 R1 0x07 N4 December 12, 2000 Senthil, Sudheer, Thomas

Senthil, Sudheer, Thomas Signaling Component Extension of the signaling protocols to carry the routing criteria Effective crankback using: Crankback at the preceding head node Primary and secondary criteria Secondary criteria is inferior to primary in terms of requirements Crankback topology feedback Signaling protocols are extended for failure condition notifications Signaling triggers CSPF under two conditions: Loose path specification Crankback occurrence (to prune the failed nodes) [draft-ietf-mpls-te-feed-01.txt] When backup LSP is required: RRO of the primary path is used CSPF during the backup calculation prunes the nodes in RRO December 12, 2000 Senthil, Sudheer, Thomas

Signaling: Inter-Area LSP Setup (ABR) R5 (ABR) R7 R3 (ABR) R1 R6 (ABR) R4 (ABR) TE-Summary-LSA PATH PATH ERROR RESV December 12, 2000 Senthil, Sudheer, Thomas

Signaling: Crankback to Preceding ABR Area 0 Area 1 Area 2 R2 (ABR) R5 (ABR) R7 R3 (ABR) R1 R6 (ABR) R4 (ABR) TE-Summary-LSA PATH PATH ERROR RESV December 12, 2000 Senthil, Sudheer, Thomas

Signaling: Use of Secondary Criteria Use of the secondary criteria to minimize crankback Area 0 Area 1 Area 2 R2 (ABR) R5 (ABR) R7 R3 (ABR) R1 R6 (ABR) R4 (ABR) Modified (Secondary) RESV PATH TE-Summary-LSA PATH RESV PATH ERROR December 12, 2000 Senthil, Sudheer, Thomas

Configuration component Routing configuration TE attributes to be summarized TE routes to be summarized LSP setup configuration Primary and secondary criteria of the LSP Signaling configuration Report of notifications December 12, 2000 Senthil, Sudheer, Thomas

Senthil, Sudheer, Thomas Conclusions Defined Concept of criteria = Set of constraints Routing extensions for inter area TE information Signaling extensions for carrying constraints and effective crankback Highlights Finds an “optimal” path to the inter-area destination If TE attribute summary available => most optimal route, less crankback If no TE attribute summary NOT available => sub-optimal route, more crankback For loose and strict source route specifications Faster connection setup time Uses secondary criteria to further reduce the possibility of crankback Uses TE feedback when crankback does need to occur Use of existing routing & signaling models (backward compatible) No new hardware/compute servers with connections into multiple areas December 12, 2000 Senthil, Sudheer, Thomas

Senthil, Sudheer, Thomas Conclusions Scenarios covered TE summary LSA propagated Loose source route: Can be computed with our modified CSPF Strict source route: Can determine apriori, if the resources are available for primary or secondary for the entire inter-area path TE summary LSA not propagated Loose source route: Reduce the crankback with the help of primary and secondary criteria Can check at the head-end of every LSP section if the resources are available for primary or secondary Scalability Routing tradeoffs between the “Selection of the optimal path” Vs. ”Granularity of the route aggregation” “Accuracy of the optimal path” Vs. “Cost of frequent routing updates/TE database” “Distributed dynamic setup” Vs. “Centralized computation” Signaling tradeoffs between the “Providing alternate criteria” Vs. “Simple crankback” December 12, 2000 Senthil, Sudheer, Thomas

Senthil, Sudheer, Thomas What next? Any suggestions, questions? Accept the following as working group documents: draft-venkatachalam-interarea-mpls-te-01.txt draft-dharanikota-interarea-mpls-te-ext-01.txt December 12, 2000 Senthil, Sudheer, Thomas