> > But my memory tells me this:
> > 
> >   - Host Unreachable should be ignored for an *existing* TCP connection
> >     (it is considered an transient error)
> >   - Host Unreachable should make a TCP connection *setup* fail
> 
> Its a heuristic some systems use. It breaks horribly on certain kinds of
> ISDN dial on demand networks, and the RFC says its a temporary error 

Hi,

OK, I can see the ISDN dod problem.
But one could argue that these routers shouldn't send an ICMP Destination
Unreachable for a packet that *can* be delivered.  It just takes some
actions (eg. bringing up the link) to accomplish it, but the destination
*is* reachable ..

I did some quick RFC-1122 scanning.  It says "TCP MUST NOT abort the
connection" (in case of a ICMP Destination Unreachable).
But there is no connection yet.  Well at least not an *established*
connection.

Anyway, I remember going through this some years ago and finding explicit
RFC indications for the second heuristic.  I'll try to find it.  Maybe I'm
wrong.  If I find something I'll be back.  Otherwise I'll shut up :-)

        Greetings,
        Rob van Nieuwkerk
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