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MPLS-TP Assumptions

Simplified BFD Procedures for Bi-Directional LSPs for MPLS OAM (particularly MPLS-TP OAM) George Swallow cisco. MPLS-TP Assumptions. Bidirectional co-routed LSPs OAM carried in an associated channel ITU standard for detection time is 10 ms Send BFD at 3.3 ms

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MPLS-TP Assumptions

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  1. Simplified BFD Proceduresfor Bi-Directional LSPsfor MPLS OAM(particularly MPLS-TP OAM)George Swallowcisco

  2. MPLS-TP Assumptions • Bidirectional co-routed LSPs • OAM carried in an associated channel • ITU standard for detection time is 10 ms • Send BFD at 3.3 ms • Needs to be simple enough for cheap silicon • Support many forms of protection switching • One difficult case !+! Bidirw/ independent switching • Consistent configuration is “guaranteed” by NMS or signaling (GMPLS)

  3. Goals • Maintain Slow Start, but greatly simplified • Elimination of Poll and Final sequences • Initial checking for agreement on timer values • Once session is up, timer values and detect mult can be ignored • Reduce the amount of session state that needs to be kept for checking validity in UP state (CC Mode) • Comparison based only on the two discriminators plus at most 2 of the first 4 bytes of the BFD packet* *Assuming Auth is not in use

  4. Summary of Changes • Poll and Final bits are not used • Timers for each direction are fixed • Deviations from these timers and the implied detect time are tied to the BFD State • Discriminator value considerations

  5. Further changes being considered • Fixed preamble for connectivity verification • Independent Mode with a single BFD session • Limited set of required timer values

  6. Timer Values • Each end is configured with Min Required RX Min Desired TX By default these will be equal, but need not be Detect Multiplier • These parameters MUST agree for session to come up

  7. Timer ValueControl • Up State: TX = configured Min Tx • Entering down state from up state Normal BFD rules apply • All other down state TX = 1 sec; detect time = 3.5 sec • Init State: TX = 1 second • Detect time in Init and Up states If no packet has been received with Up state; Detect timer = 3.5 seconds • (these procedures assume Tx and Rx < 1 second) Detect time changes on receipt of an UP state from neighbor toDetect_Mult*Min Rx

  8. Discriminators “My Discriminator” is locally configured Optionally “your discriminator” value MAY be configured with the following procedures During session initialization • If the received “my discriminator” does not match the configured “your discriminator”, the session remains in the down state In Up and Init States • If the received “My Discriminator” changes the session MAY be declared Down • Latter case is what is expected in a configured environment

  9. Example of Initialization B (DOWN) A(DOWN) TX @ 1 second MyDisc=B32; YourDisc=0 TX @ 1 second Down 10 msec/10 msec MyDisc=A26; YourDisc=0 Down 10 msec/10 msec B Sta (INIT) TX @ 1 second A Sta (UP) TX @10 msec MyDisc=B32; YourDisc=A26 INIT 10/10 msec MyDisc=A26; YourDisc=B32 UP 10/10 msec A Sta (UP) TX @10 msec Change Detect Time A Sta (UP) TX @10 msec Change Detect Time MyDisc=B32; YourDisc=A26 UP 10/10 msec

  10. Fixed Preamble • Used to hold • ASN & IPv4 source and destination • various forms of OAM identifiers (MEG-IDs) • Many possibilities for formats and identification of formats • Nothing decided at this point • Size in packet is not a great issue; size of state per session is a big issue

  11. Independent Mode Single Session • Session Initiation same as bi-directional mode • On • Control Detection Time Expired (1) • Path Down (5) • Send diag (both imply RDI), but stay in UP state • Only enter down state on • Returning from a complete reset of LSP • Admin Down • Neighbor signals Down

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