nanog mailing list archives
Re: ISP port blocking practice
From: Claudio Lapidus <clapidus () gmail com>
Date: Sun, 5 Sep 2010 14:36:30 -0300
Hello all, On Fri, Sep 3, 2010 at 11:30 PM, Ricky Beam <jfbeam () gmail com> wrote:
If I block port 25 on my network, no spam will originate from it. (probablly) The spammers will move on to a network that doesn't block their crap. As long as there are such open networks, spam will be rampant. If, overnight, every network filtered port 25, spam would all but disappear. But spam would not completely disappear -- it would just be coming from known mailservers :-) thus enters outbound scanning and the frustrated user complaints from poorly tuned systems...
That won't be probably the case. Here recently we conducted a rather comprehensive analysis on dns activity from subscribers, and we've found that in IP ranges that already have outgoing 25 blocked we were still getting complaints about originating spam. It turned out that the bots also know how to send through webmail, so port 25 blocking renders ineffective there. --cl.
Current thread:
- RE: ISP port blocking practice, (continued)
- RE: ISP port blocking practice Paul Stewart (Sep 03)
- Re: ISP port blocking practice Doug Barton (Sep 03)
- Re: ISP port blocking practice Franck Martin (Sep 03)
- Re: ISP port blocking practice Owen DeLong (Sep 03)
- Re: ISP port blocking practice John R. Levine (Sep 03)
- Re: ISP port blocking practice Robert E. Seastrom (Sep 08)
- RE: ISP port blocking practice Brian Johnson (Sep 12)
- Re: ISP port blocking practice Patrick W. Gilmore (Sep 03)
- Re: ISP port blocking practice Ricky Beam (Sep 03)
- Message not available
- Re: ISP port blocking practice Patrick W. Gilmore (Sep 03)
- Re: ISP port blocking practice Claudio Lapidus (Sep 05)
- Re: ISP port blocking practice Patrick W. Gilmore (Sep 05)
- Re: ISP port blocking practice Franck Martin (Sep 05)
- Re: ISP port blocking practice Paul Ferguson (Sep 05)
- Re: ISP port blocking practice Jon Lewis (Sep 05)
- Re: ISP port blocking practice Owen DeLong (Sep 05)
- Re: ISP port blocking practice Franck Martin (Sep 05)
- Re: ISP port blocking practice Jon Auer (Sep 06)
- Re: ISP port blocking practice Scott Howard (Sep 11)
- Re: ISP port blocking practice Brett Frankenberger (Sep 06)
- Re: ISP port blocking practice Patrick W. Gilmore (Sep 06)