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

[James Bensley]

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.

Cheers,
James.