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. Frank -----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Mark Foster Sent: Friday, March 07, 2008 10:02 PM To: Dave Pooser Cc: nanog@merit.edu Subject: Re: Customer-facing ACLs
Blocking port 25 outbound for dynamic users until they specifically request 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 started 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 my 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? Mark.