Junos OS

Expand all | Collapse all

Inline BFD vs distributed BFD

  • 1.  Inline BFD vs distributed BFD

    Posted 05-31-2019 02:04

    Hello everyone


    I don't know the difference between inline BFD and distributed BFD.


    I found Inline means that BFD/FLOW service run from PFE. so distributed BFD is equal to inline BFD?


     I'd be grateful if someone could tell me the difference in detail.


    Thanks in advance.

  • 2.  RE: Inline BFD vs distributed BFD

    Posted 05-31-2019 03:00



    Distributed Mode is that Periodic packet management (ppmd) which is the daemon responsible for BFD is to be run on Routing Engine's CPU and line cards CPU , this is as opposed to centralized mode where it will be run on RE only.

    Inline mode delegates the processing  to the forwarding ASIC (that is, to the hardware). By enabling inline mode the load on the CPU of the line-card is reduced and also  faster transmit and more aggressive detect time is achieved.



  • 3.  RE: Inline BFD vs distributed BFD

    Posted 06-02-2019 21:49



    That was very helpful, thank you!



  • 4.  RE: Inline BFD vs distributed BFD

    Posted 05-31-2019 06:43

  • 5.  RE: Inline BFD vs distributed BFD

    Posted 08-14-2020 03:27

    explained very well under the section  "Periodic packet management daemon" 





    there is actual slight difference between distributed and inline bfd session. We can safely say that inline is enhanced version of distributed mode. 


    Distributed Mode:-


    For several years, ppmd has not been a single process hosted on the Routing Engine and now it has been developed to work in a distributed manner. Actually, ppmd runs on the Routing Engine but also on each Trio line card, on the line card’s CPU, where it is called PPM Manager, also known as ppm man. The following PFE command shows the ppm man thread on a line card CPU:

    NPC11(R1 vty)# show threads
    54 M  asleep    PPM Manager           4664/8200   0/0/2441 ms  0%

    The motivation for the delegation of some control processing to the line card CPU originated with the emergence of subsecond protocols like BFD.


    Inline Mode:- (it is only not limited to Trio chipset but also Available in latest Broadcom Trident chipsets) 


    Recently, the Trio line card offers a third enhanced version of ppm, driven also by the BFD protocol in scaled environments, which is called inline ppm. In this case, the Junos OS has pushed the session management out to the packet forwarding engines themselves


    we can disable distributed and inline ppmd via 


    set routing-options ppm no-delegate-processing
    set routing-options ppm no-inline-processin