Finding asymmetric path

Suresh Ramasubramanian ops.lists at
Sat Nov 28 21:02:31 CST 2009

Yes - term the account would be my recommendation

And if you filter port 25 traffic do it both ways

Read these old nanog threads .. and[email protected]/msg28863.html

On Sun, Nov 29, 2009 at 3:58 AM, William Herrin
<herrin-nanog at> wrote:
> On Sat, Nov 28, 2009 at 2:14 PM, ML <ml at> wrote:
>> Brielle is correct.  The customer in question is spamming networks and we
>> are having trouble filtering them because another provider allows them to
>> source traffic however they please.
> What trouble? SMTP requires two-way traffic with a static port number
> that nothing else uses. If for some reason you don't want to simply
> terminate their account altogether, block packets outbound to your
> customer sourced from TCP port 25 but not from your SMTP smarthosts.
> Seriously though, if you can prove they're spamming (regardless of
> whether the packets pass through your network) save yourself some
> grief and just terminate the account.
> Regards,
> Bill Herrin
> --
> William D. Herrin ................ herrin at  bill at
> 3005 Crane Dr. ...................... Web: <>
> Falls Church, VA 22042-3004

Suresh Ramasubramanian (ops.lists at

More information about the NANOG mailing list