Re: RE: AD request / L2 Triggers Chapter Statement

Lloyd Wood wrote:
> On Fri, 5 Jul 2002, Joe Touch wrote:
>>
>>Given that IP is stateless and connectionless,
> 
> 
> As if.
> 
> A link interface is allocated an IP address and mask. That's state.
> The link interface is either up or down. That's your immediate
> connection to the subnet.

That's not IP state. That's link state. There's nothing IN IP that knows 
about that assignment.

> (and ICMP is all about telling others about your IP state.)

ICMP is to indicate errors, but not stateful ones. The error can easily 
have disappeared, or the message can be deleted.

>>There is no way to push information through a stateless system into a
>>stateful one (e.g., TCP, or to application layers, e.g., routing
>>protocols or user applications that are carried as data inside transport
>>protocols).
> 
> You're saying that if a link goes down there's no way to tell routing
> about it, because IP gets in the way and routing is above IP?

That sort of info is a MIB. It isn't passed via IP, so much as 
transparently through it.

There is no place _IN_ IP to store the "this link is down" state, as 
noted above.

> (Fortunately, routers that know about links and know about routing
> tables can use the information regardless if it's useful.)

Routers know out-of-band info about links, communicated as data already. 
If this is all about arguing for a MIB, why? Just do it.

> When the link on a host goes down, will the TCP stack continue to
> accept data from the application even though it can't be sent? (Phil's
> kick-TCP-when-the-link-comes-up also springs to mind.)

A link on a host going down isn't enough; the host might be multihomed, 
at which point routing comes into play. And where's that routing - on 
the host, or a few hops down?

You really want to kick TCP whem a phone line 100 miles away goes down, 
even if it isn't necessarily connected to your machine? That's what 
routing is for.

----

What appears to be desired here is:

	a realtime MIB for link state
	a routing protocol that reads and reacts to the MIBs on
	microsecond timescales

None of this is IP.

Joe




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