North American Network Operators Group

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Re: Customer-facing ACLs

  • From: Justin M. Streiner
  • Date: Fri Mar 07 15:11:40 2008

On Fri, 7 Mar 2008, Justin Shore wrote:

Do you block any customer-facing egress traffic at all? What about ingress? SMTP, NetBIOS, MS-SQL, common proxy ports (3128, 6588)?

What ICMP types do you allow or disallow?

In my previous life, I worked at a mid-sized ISP. A common practice for bridged DSL customers was to block outbound traffic to the various Netbios ports, along with a few other ports that were added at the time to keep Slammer and friends under control. We also deployed filters through RADIUS that covered much of the same ground for dialup and PPPoE DSL users and it worked reasonably well.

I do recall weighing the merits of extending that to drop outbound SMTP to exerything except our mail farm, but it wasn't deployed because there was a geat deal a fear of customer backlash and that it would drive more calls into the call center.