Re: Failure Detection (was Re: soft state (was Re: shim6 and bit errors in data packet headers

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 6-jun-2005, at 20:12, Erik Nordmark wrote:

> In my mind, given that some ULPs might not provide any advice and  
> we want to provide failover on that case, we need the default  
> behavior of the shim to be to probe at some frequency (once every  
> 10 seconds or so?) when the ULP is sending packets.

Probing when you're sending is rather superflous: you're already  
sending in that direction so no need to send more. Having the other  
end send keepalives accomplishes the same thing with lower overhead:  
you get feedback that the other end is still there, but packets only  
flow in the otherwise idle direction.

> Once we have the above, then I don't see what negative ULP advice  
> would add. We clearly can't always send probes on negative advice,  
> since that could mean that a congestive loss in the network would  
> result in negative ULP advice, causing the host to send more  
> packets, which could make the congestion worse.

:-)

Well I would hope it would result in a rehoming so a non-congested  
path would be selected.

> If ULPs with different desires use the same ULID pair, then  
> presumably the shim would have to operate on the minimum of the  
> requested times. And the shim presumably needs to ensure that it  
> doesn't try to probe more frequently than a conservative RTT  
> estimate no matter what the ULPs desire.

Conservative RTT could be 1 ms on fast ethernet...