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Composite Link Framework Issues

Composite Link Framework Issues. Functional requirement #1. The solution SHALL provide a means to summarize routing advertisements regarding the characteristics of a composite link such that the routing protocol converges within the timeframe needed to meet the network performance objective.

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Composite Link Framework Issues

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  1. Composite Link Framework Issues

  2. Functional requirement #1 The solution SHALL provide a means to summarize routing advertisements regarding the characteristics of a composite link such that the routing protocol converges within the timeframe needed to meet the network performance objective.

  3. To Aggregate or Not? • Pro: • More scalable: less information in IGP • Quicker path computation (NBD) • Con: • Crankback during signaling

  4. Crankback • Loop • Compute path across network • Signal path • If success, exit • Exclude link that just failed • Iterate

  5. Costs of crankback • Still have to advertise composite link in IGP • Only saved components • Each failed signaling attempt takes time • There may not be a working path • Ergo: signaling may take an arbitrarily long time • Failure information from one setup may not apply to another: start over

  6. Benefits of crankback • Skip characterizing component • Max bandwidth (4B + 2B overhead) • Max reservable bandwidth (4B + 2B overhead) • Unreserved bandwidth (4B + 2B overhead) • Latency (4B float + 2B overhead) • Component Index (4B id + 2B overhead) • Delay variation (4B id + 2B overhead) • TLV overhead (2B) • Total: 36B per component

  7. IS-IS scalability • IS-IS LSP space: 256 possible fragments • Fragment: 1200B, partially filled, fixed header • Estimate: 80% fill • Some overhead for other TLVs: 75% fill • Available space: 230KB -> 7,000 components • Flooding time: 230KB @ 1Gb/s ~= 2ms • Incremental flooding makes this MUCH shorter • Typically 1 LSP

  8. More LSP space • Increase fragment size • Jumbo frames • More fragments: RFC 5311 • Add additional system IDs • Gives 256 fragments per ID

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