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draft- litkowski - rtgwg - spf - uloop - pb -statement IETF 90 - Toronto

draft- litkowski - rtgwg - spf - uloop - pb -statement IETF 90 - Toronto. S. Litkowski , Orange. Introduction. The draft analyses how different implementations of IGP link state protocols may favor microloops

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draft- litkowski - rtgwg - spf - uloop - pb -statement IETF 90 - Toronto

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  1. draft-litkowski-rtgwg-spf-uloop-pb-statementIETF 90 - Toronto S. Litkowski, Orange

  2. Introduction • The draft analyses how differentimplementations of IGP link state protocolsmayfavormicroloops • The draftdoes not propose any solution but calls for standardizingsome new components of IGP (apart of the protocolitself)

  3. Microloops (reminder …  ) • Trafficgoesfrom S to D • When SD fails, if D converges before E, the trafficwillloopuntil E has converged • Whytaking care about microloops ? • Seeourotherdraft : • draft-ietf-rtgwg-uloop-delay S ---- E | | 10 | | 10 | | D ---- A 2

  4. IGP convergence influence on microloops • IGP convergence time differencebetweennodesiscritical in the microloopphenomenon • Components of IGP LinkState convergence : • Detection(direct or indirect throughprotocol notification) • SPF delay • SPF computation time • RIB/FIB insertion May favormicroloops May behundreds of msec (theorically) Hundreds of msec or seconds NegligeablewithcurrentCPUs (x msec) HW and implementations are more and more powerful in this area

  5. SPF trigger strategies • Multiple implementationexists : • Alwayscompute full SPF • Run Full SPF onlywhenrequired • If a linkfails, twoLSPs are sent, if a SPF has already been computed for LSP1, thereis no need to run full SPF for LSP2 (topology has not change) • If topologydoes not change, onlyrecomputesreachability

  6. SPF delaystrategies • Most (all) implementations are introducing variable delaysbefore running SPF in order to manage churns • Major implementations : • Exponentialbackoff • Twosteps (rapid/slow mode) SPF delay time ^ MD- | xx x | | | | | | x | | | | x | FD- | x xx ID | +---------------------------------> Events | | | | || | | < wait time > FM->BM -------------------->FM SPF delay time ^ | | SD- | x xx x | | | RD- | x xxx | +---------------------------------> Events | | | | || | | < wait time >

  7. Mixingstrategies in a network • Consider : • S strategy : • Full SPF triggeredonlywhennecessary • Twostep SPF delay (Rapid=150ms,Rapidruns=3,Slow=1s) • Separatetimerisused for SPF delay and PRC delay but same values • E strategy : • Alwayscompute full SPF (no PRC) • Exponentialbackoff SPF delay (FD=150ms,ID=150ms,max=1s) S ---- E | | 10 | | 10 | | D ---- A 2

  8. Mixingstrategies in a network S timescale E timescale Event timescale | | | | | | <- t0 Event prefix down | Schedule PRC (150ms) | Schedule SPF (150ms) | | | | | | | | | | | PRC starts | SPF starts | | PRC ends | | | RIB/FIB starts | SPF ends | | | RIB/FIB starts | | RIB/FIB ends | | | | RIB/FIB ends | t0+180ms | | | | | | < - t0+200ms Event prefix up | Schedule PRC (150ms) | Schedule SPF (150ms) | | | | | | | | | | | PRC starts | SPF starts | | PRC ends | | | RIB/FIB starts | SPF ends | | | RIB/FIB starts | | RIB/FIB ends | | | | RIB/FIB ends | t0+380ms | | | < - t0+400ms Event prefix down | Schedule PRC (300ms) | Schedule SPF (300ms) | | | | | | | | | | | | | S ---- E | | 10 | | 10 | | D ---- A 2

  9. | | | | | | | PRC starts | SPF starts | | PRC ends | | | RIB/FIB starts | SPF ends | | | RIB/FIB starts | | RIB/FIB ends | | | | RIB/FIB ends | t0+730ms | | | | | | | | | | | | | | | < - t0+1000ms Event link S-D down | Schedule SPF (150ms) | Schedule SPF (600ms) | | | | | | | | SPF starts | | | | | | SPF ends | | | RIB/FIB starts | | | | | } | RIB/FIB ends | | } | | | } | | | } | | | } | | | } | | | } Micro-loop creation | | | } | | SPF starts | } | | | } | | SPF ends | } | | RIB/FIB starts | } | | | } | | RIB/FIB ends | } S ---- E | | 10 | | 10 | | D ---- A 2 Misalignement of SPF delays

  10. Proposedwork items • Standardize SPF trigger strategy • Standardize SPF timer scope : • Single timer for all computations, or multiple … • Standardize progressive SPF delayalgorithm

  11. Non goal • Otherparametersmaybestandardizedlikefloodingstrategies • Floodingstrategies are criticalpiece of codes in implementationthatmaybe not soeasy to touch …

  12. What’snext ? • WG feedback ? • Do WG considerthatthisis an item to work on ? • We DO ! • Simple to agree and implement … and will help to minimizemicroloops duration or occurrences.

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