RE: ISP port blocking practice

["Brian Johnson" <bjohnson () drtel com>]

Brian J.

> -----Original Message-----
> From: Ricky Beam [mailto:jfbeam () gmail com]
> Sent: Friday, September 03, 2010 9:30 PM
> To: Owen DeLong; Patrick W. Gilmore
> Cc: NANOG list
> Subject: Re: ISP port blocking practice
>
> On Fri, 03 Sep 2010 08:12:01 -0400, Owen DeLong <owen () delong com>
> wrote:
> > Really?  So, since so many ISPs are blocking port 25, there's lots
less
> > spam hitting our networks?
>
> Less than there could be.  It appears a lot less effective because
there
> are so many ISPs not doing any blocking.  Both of my residential
> connections are open, and always have been. (even dialup was unblocked.
> which I always found odd since the UUNET wholesale dialup agreement
> requires the RADIUS response contain a packet filter limiting port 25
to
> your mail server(s).)
>
> If I block port 25 on my network, no spam will originate from it.
> (probablly) The spammers will move on to a network that doesn't block
> their crap.  As long as there are such open networks, spam will be
> rampant.  If, overnight, every network filtered port 25, spam would all
> but disappear.  But spam would not completely disappear -- it would
just
> be coming from known mailservers :-)  thus enters outbound scanning and
> the frustrated user complaints from poorly tuned systems...
>
> --Ricky

This is what we (network admins) get paid to do! If we are running a
server that is a security risk to the net, then we can't complain when
it gets filtered. It is our job to do our due diligence and ensure our
servers are not spam hot-beds or open relays (or other bad stuff,
etc...).

The port 25 blocking simply prevents the largest volume of hosts in an
ISP network, the users, from being a spam delivery platform.

- Brian


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