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SubjectRe: 2.2.2-ac7 TCP ignores ICMP host unreachable ??
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Rob van Nieuwkerk wrote:
> > > 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 :-)

Well, your above quote seems to "allow" the 2.0 behaviour.

When you've got an established connection, you KNOW it is a temporary
error: you reached the host during connection setup just fine. This
implies that you can safely guess that it is a permanent error when
you get it on the connection setup.

The people who get a "host is unreachable try again later, if the
problems persist, contact the systems administrator" window, are
invited to try again later. Two seconds later should work.

Even if RFCs recommend the 2.2 behaviour, I'd personally like an
option to be non-RFC compliant. We already have those (always-defrag
comes to mind).


Regards,

Roger.


--
** R.E.Wolff@BitWizard.nl ** http://www.BitWizard.nl/ ** +31-15-2137555 **
*-- BitWizard writes Linux device drivers for any device you may have! --*
* Never blow in a cat's ear because if you do, usually after three or *
* four times, they will bite your lips! And they don't let go for at *
* least a minute. -- Lisa Coburn, age 9

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