Re: [exim] SMTP connection lost

On Thu, 2010-08-12 at 21:17 -0400, W B Hacker wrote:
> Grep the list archives. ISTR an issue two or more years ago wherein some (many?)
> broadband providers were - in essence - 'stealing' bytes for one overhead reason
> or another, AND ICMP was now-and-then firewalled (or ignored?), so the hosts
> could not negotiate a mutually useful MTU size - at least for anything that
> needed a full MTU (HELO and other basic 'handshakes' would not, but headers
> probably would, 'DATA' almost always would do...).
>
> Not (exclusively) an Exim issue - it's 'sub-optimal' configuration of the
> underlying TCP/IP...

I wouldn't describe that as 'sub-optimal' -- even with the quotes. It's
broken, plain and simple.

If ICMP is filtered and you can't ping the host you're trying to
communicate with, then all bets are off. Thinks might *look* like they
work at first glance, but they're quite likely to be broken.

If you're trying to diagnose any kind of network issue and ICMP is not
getting through, then fix that before attempting to do *anything* else.

(It *is* possible to filter only certain types of ICMP, so connectivity
is only mildly broken and TCP connections actually work OK. But most
people clueless enough to filter ICMP at all are also clueless enough to
get that wrong.)

--
dwmw2