Re: failure detection

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

On 14-aug-2005, at 16:49, Paul Jakma wrote:

> > An implementation that uses upper layer advice would only initiate  
> > a probe/reply sequence when the upper layer is unhappy.

> This kind of thing worries me.

Apparently... I don't really get why, though.

> Assuming it will be possible to have the upper layer 'direct' shim6  
> is assuming:

> - OS maintainers will be prepared fundamentally change their network
>   stacks to support shim6

Well, obviously they have to implement it or it won't work, no pain  
no gain.  :-)

> - Worse, assuming upper layers even /have/ a notion of being
>   unhappy or happy.

I'm sure there will be ones that have such a notion and equally sure  
there are ones that don't.

> Don't try get clever, cause the upper layer knows /more/ than shim6  
> does:

Just now you questioned whether the upper layer knows enough to be  
unhappy!

> - It might have a list of addresses it wants to try, don't delay it

It doesn't. The application may have a list of addresses, but TCP or  
UDP only see a single one.

> It is *much* better for the data-layer to signal *up*:

>     "sorry, it's unreachable"

> as soon as it can, and let the transport or the application or  
> maybe even the *user* get on with trying potential alternatives  
> than for the data-layer to try aimlessly continue on for a  
> significant period of time with complicated reachability tests.

So basically you're saying that applications can multihome better  
than the network stack? I disagree.