[ILUG] ESMTP weirdness with one of {cisco|adsl}

[Ronan Waide]

Hi folks,

A little off-topic for ILUG, but.

I'm digging into a problem here that's making no sense. I've got a
mail server sitting behind a Cisco which talks to the rest of the
world via an ADSL line provided by eircom. At present, if I try using
EHLO to any server anywhere, I get a 502 response. This obviously
means I can't go pick up mail from my secondary MXs, because no EHLO
-> no ETRN.

So.

In pursuit of this problem, I've done a variety of tests and tcpdumps
and ethereal traces and what not. Suffice to say it looks like
something is filtering the SMTP channel, converting my outbound EHLO
to NOOP, and converting the response (250) to 502.

If I try another port, e.g. run up a sendmail server on port 4242 and
EHLO to that, I get a 250 response like I'd expect. I'm pretty sure
that all the Cisco is doing here is providing NAT services, since
filtering EHLO seems to me like something you'd have to explicitly
enable in the config somewhere.

So. Am I to arrive at the conclusion that Eircom are messing with my
EHLO stream, or is this some new Cisco feature I should be aware of?
And if the latter, how do I turn the damn thing off?

Cheers,
Waider.

ObLinux: I've been using a variety of Linux servers for my tracing :)
-- 
waider at waider.ie / Yes, it /is/ very personal of me.

buzzard says, "If you are willing to put aside your kneejerk human speciesism,
    the AIs are perfectly sympathetically 'no worse' than humans." <matrix>