Simplified BFD Procedures
1 / 11

MPLS-TP Assumptions - PowerPoint PPT Presentation

  • Uploaded on

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

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about ' MPLS-TP Assumptions' - espen

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Simplified BFD Proceduresfor Bi-Directional LSPsfor MPLS OAM(particularly MPLS-TP OAM)George Swallowcisco

Mpls tp assumptions
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)


  • 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

Summary of changes
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

Further changes being considered
Further changes being considered

  • Fixed preamble for connectivity verification

  • Independent Mode with a single BFD session

  • Limited set of required timer values

Timer values
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

Timer value control
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


“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

  • Example of initialization
    Example of Initialization

    B (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

    Fixed preamble
    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

    Independent mode single session
    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