[c-nsp] BFD on ME3600/ME3800/7600s

[Adam Vitkovsky]

> James Bensley
> Sent: Friday, May 27, 2016 7:21 PM
>
> On 27 May 2016 at 18:07, Adam Vitkovsky <Adam.Vitkovsky at gamma.co.uk>
> wrote:
> >> James Bensley
> >> Sent: Friday, May 27, 2016 2:28 PM
> >> To: cisco-nsp at puck.nether.net
> >> Subject: Re: [c-nsp] BFD on ME3600/ME3800/7600s
> >>
> >> In echo mode the local node sends echo packets at the specified
> >> interval of 50ms, the remote node loops them back in hardware
> >> (because they are UDP packets they shouldn't be punted to the CPU)
> >> and the local node receives and checks it's own echo packets.
> >>
> > Hmmm and what about the remote node?
> > If all the remote node does is looping packets back in HW -how does it
> know that the link is still operational please?
>
> It works the same as I described for the local node. So above I have only
> described the operations of BFD echo mode from the perspective of just one
> node, the "local" node. BFD in echo mode does have to be configred on both
> nodes it you want both nodes to support bidirectional forwarding detection.
>
> > So in echo mode only one node is sending echo packets and the other
> node is just responsible for looping them?
> > I was under the impression that if you configure BFD echo mode on both
> ends then both ends will TX and check own packets as well as loop each
> other's packets.
> > Also I would have thought that in echo mode since each side is responsible
> for checking its own packets independently of the remote end then each
> side can also run its own timers -though I'm not sure if also in echo mode
> there's timers negotiation that makes sure one doesn't shoot himself in the
> foot.
>
> Yeah so two back-to-back routers R1 and R2. R1 sends echo packets, R2 loops
> them back, R1 checks them. R2 sends packets, R1 loops them back,
> R2 checks them. As I said above, I was just describing the operations from
> the perspective of one node which I called the "local" node.
>
> Apologies if what I originally said wasn't clear.
>
Alright then so indeed nodes participating in echo mode have to do more work as nodes participating in non-echo mode. That's why assume it performs slower (comparing performance of both modes in SW).

To do list of one of the nodes in non-echo mode:
Tx at a given rate.
Reset dead timer if hello from remote node received.

To do list of one of the nodes in non-echo mode:
Tx at a given rate.
Reset dead timer if own hello received.
Loop partner's hellos at a given rate.
-I'm not sure but doesn't it also put local time while looping to facilitate one way delay measurement?


adam


        Adam Vitkovsky
        IP Engineer

T:      0333 006 5936
E:      Adam.Vitkovsky at gamma.co.uk
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