North American Network Operators Group

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RE: Customer-facing ACLs

  • From: Frank Bulk
  • Date: Sat Mar 08 00:33:47 2008

The last few spam incidents I measured an outflow of about 2 messages per
second.  Does anyone know how aggressive Telnet and SSH scanning is?  Even
if it was greater, it's my guess there are many more hosts spewing spam than
there are running abusive telnet and SSH scans.  


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Mark
Sent: Friday, March 07, 2008 10:02 PM
To: Dave Pooser
Cc: [email protected]
Subject: Re: Customer-facing ACLs

> Blocking port 25 outbound for dynamic users until they specifically
> it be unblocked seems to me to meet the "no undue burden" test; so would
> port 22 and 23. Beyond that, I'd probably be hesitant until I either
> getting a significant number of abuse reports about a certain flavor of
> traffic that I had reason to believe was used by only a tiny minority of
> own users.

Sorry, I must've missed something.
Port 25 outbound (excepting ISP SMTP server) seems entirely logical to me.

Port 22 outbound? And 23?  Telnet and SSH _outbound_ cause that much of a
concern? I can only assume it's to stop clients exploited boxen being used
to anonymise further telnet/ssh attempts - but have to admit this
discussion is the first i've heard of it being done 'en masse'.

It'd frustrate me if I jacked into a friends Internet in order to do some
legitimate SSH based server administration, I imagine...

Is this not 'reaching' or is there a genuine benefit in blocking these
ports as well?