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Old 12-01-2003, 05:24 PM   #1
Registered: Jun 2003
Posts: 92

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comcast smtp port 25


i had comcast cable internet.
I setup a qmail server, i was enable to send email from LAN, and i was able telnet 25

but i wasn't able to telnet it from outside... i was able to telnet from outside in port 21(ftp)..

i wonder are there any one having the same problem as my...

Old 12-01-2003, 06:47 PM   #2
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Registered: Jul 2003
Location: Silicon Valley, USA
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Comcast probably does block inbound connections on port 25/tcp. You can verify this by using a crossover cable to plug a computer (laptop is easy) into the external interface of your route/gateway (could be the "WAN port" on those Linksys/D-Link/etc "broadband routers" or the outside NIC if you're using a dual-homed PC as a gateway). Make sure you give your laptop an IP from the DHCP pool for Comcast (try giving it your normal gateway address) and then telnet to your external Internet IP on port 25.

So here's how it would work...

Say you have a Linksys broadband router. The WAN port plugs into your cable modem. The WAN port gets the IP, your gateway on the Comcast side is Your LAN network is (or /16, or whatever) and the inside IP of the router is

What you want to do is configure your laptop with the IP and plug it directly into the WAN port (remove the cable going to the cable modem). Now telnet 25... If it works, then Comcast is blocking port 25. Tough luck If it does not work, then you have your firewall misconfigured.
Old 12-02-2003, 09:43 AM   #3
Registered: Oct 2003
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>but i wasn't able to telnet it from outside

It is also possible that the ISP you tried to connect from has blocked outgoing port 25 connections.
Old 01-02-2005, 12:19 AM   #4
Edward Reponte
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Registered: Jan 2005
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Cool Setup the PORT Forwarding in the Router

I have a single COMCAST Broadband connection too. I set up the Port Forwarding in the Router to allow FTP, TELNET, SSH and HTTP request to be forwarded to another host beyond the router. I have a Linksys too.

Hope this helps.



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