I Second that. AT&T blocks ports (depending where you are) but won't come right out and say it. On a call to them over a year ago while testing DSL versus Cable in San Jose, it took almost an hour to get them to admit that they were blocking ports 137-139, and even then there was no formal acknowledgement of this blocking. If I was a betting man, which I'm not, I'd bet on them blocking udp 53 as well. No standard as I see it, depends on the child company managing the cable service. Just my 2¢s tho -Joe ----- Original Message ----- From: "Joseph Barnhart" <flaboy@fdt.net> To: "Matthew S. Hallacy" <poptix@techmonkeys.org> Cc: <nanog@merit.edu> Sent: Sunday, October 27, 2002 8:46 PM Subject: Re: How to secure the Internet in three easy steps
Not really
On Sun, 27 Oct 2002, Matthew S. Hallacy wrote:
On Sun, Oct 27, 2002 at 02:35:23PM -0500, Eric M. Carroll wrote:
Sean,
At Home's policy was that servers were administratively forbidden. It ran proactive port scans to detect them (which of course were subject
to
firewall ACLs) and actioned them under a complex and changing rule set. It frequently left enforcement to the local partner depending on contractual arrangements. It did not block ports. Non-transparent proxing was used for http - you could opt out if you knew how.
While many DSL providers have taken up filtering port 25, the cable industry practice is mostly to leave ports alone. I know of one large
Untrue, AT&T filters the following *on* the CPE:
Ports / Direction / Protocol
137-139 -> any Both UDP any -> 137-139 Both UDP 137-139 -> any Both TCP any -> 137-139 Both TCP any -> 1080 Inbound TCP any -> 1080 Inbound UDP 68 -> 67 Inbound UDP 67 -> 68 Inbound UDP any -> 5000 Inbound TCP any -> 1243 Inbound UDP
And they block port 80 inbound TCP further out in their network. Overall, cable providers more heavily than cable providers.
I'd say that AT&T represents a fair amount of the people served via cable internet.
Regards,
Eric Carroll
-- Matthew S. Hallacy FUBAR, LART, BOFH Certified http://www.poptix.net GPG public key 0x01938203
------------------------- Joseph Barnhart Florida Digital Turnpike Network Administrator http://www.fdt.net http://www.agilitybb.net -------------------------