1. Simplified BFD Procedures for Bi-Directional LSPs

2. Goals Simple static configuration of Active State Maintain Slow Start, but greatly simplified – Fixed values for timers, detect multiplier during session (re- )initialization – 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 *Could be reduced further pending discussion of control bits

3. Summary of Changes since IETF 77 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

4. 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

5. Timer Value Control Up State On entering the 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 to Detect_Mult*Min Rx

6. 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

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

8. Further Simplifications Eliminate ACH TLVs Modify procedures for Independent Mode such that there is only one BFD session needed Limited set of timer values that are required to be supported

9. Eliminate ACH TLVs Replace with a fixed preamble which can contain – various forms of MEG-IDs – other identifiers 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

10. 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