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.
there is actual slight difference between distributed and inline bfd session. We can safely say that inline is enhanced version of distributed mode.
For several years,ppmdhas not been a single process hosted on the Routing Engine and now it has been developed to work in a distributed manner. Actually,ppmdruns on the Routing Engine but also on each Trio line card, on the line card’s CPU, where it is calledPPM Manager, also known asppm 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
Please mark this as accepted solution if it works for you