Re: 2.2.2-ac7 TCP ignores ICMP host unreachable ??

Rob van Nieuwkerk (robn@verdi.et.tudelft.nl)
Thu, 04 Mar 1999 02:14:07 +0100

> > 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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