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

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

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