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RE: Cable Modems Need Open Ports?
From: "Mike Marcus" <mmarcus () nelsonpub com>
Date: Mon, 4 Nov 2002 16:20:20 -0500

To All,
        Thanks again for all your replies.  It appears that since my new DOCSIS
modem any changes filter changes I make to the netgear router will cause the
problem.  If I power down the modem and router, power up the modem and then
the router everything is just fine.  This symptom did not show up with my
older cable modem (pre-DOCSIS).  So this appears to be a sync problem
between the router and the modem.  Once they are up, all is fine.  I will be
getting another router with more firewall features and will try it with the
new modem.  Thanks again to all who participate.  The information is


-----Original Message-----
From: Raoul Armfield [mailto:armfield () amnh org]
Sent: Monday, November 04, 2002 3:27 PM
To: Case CCC; Mike Marcus
Cc: security-basics () securityfocus com
Subject: RE: Cable Modems Need Open Ports?

I have a linksys router with a cable modem and have block everything
incoming and have no problems resolving dns names.  It seems to me that it
shouldn't need to connect through port 53 since you are making the requests.
Isn't port 53 listening for inbound requests?

:-----Original Message-----
:From: Case CCC [mailto:case_list () operamail com]
:Sent: Saturday, November 02, 2002 12:46 AM
:To: Mike Marcus
:Subject: Re: Cable Modems Need Open Ports?
:I believe port 53 is required to resolve the namespaces,
:like yahho.com to 64.58.79.x... Also, port 59 is used
:by new file to talk back and forth to the server that
:keeps the token lists.
:I would recommend doing a google search with
:'TCP/IP Ports 53 59'
:Try blocking one or the other see what happens,
:trial and error is a harsh mistress but a great
:external IP i assume you mean the WAN side on you
:router/modem NIC.
:> I was "playing" with setting on my router that is connected to a
:cable modem
:> (Comcast is the ISP).  After blocking incoming (from wan) UDP
:and TCP ports
:> 53 and 59 the router lost its external IP.  Any ideas?
:> Thanks,
:> Mike
:Get your free email from http://mymail.operamail.com
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