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Tyler
join:2010-06-04
North East, PA

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Tyler

Member

[Connectivity] DPC3939 and Web Server/Camera

I don't know the specific terminology to use, so bear with me.

I have the Xfinity X1 package with the DPC3939 Gateway Modem. I have a security camera management page that simply runs over port 80 and a camera that runs on port 1234 (as an example). With the proper port forwarding in place, I can successfully access the page and camera from an outside network, however while I am on my WiFi or LAN, I cannot access the pages as I normally would by going to »webpage.com as it seems like there is some type of issue with LAN requests going out and coming back through the WAN.

Has anyone else with this modem experienced this, maybe anyone that is running any type of web server? I know I read something about it somewhere that this modem/gateway doesn't support lan to wan requests, but I'm at a loss for finding that article.

NetFixer
From My Cold Dead Hands
Premium Member
join:2004-06-24
The Boro
Netgear CM500
Pace 5268AC
TRENDnet TEW-829DRU

2 edits

NetFixer

Premium Member

Re: DPC3939 and Web Server/Camera

I am not familiar with that particular gateway box, but it is a fairly common symptom for resi/soho NAT routers to not properly support what is called NAT Loopback. The Comcast business class SMC gateway is an example of a Comcast gateway that I do know does not support NAT loopback (one of the reasons that I dumped it).

The most common workaround is to create a hosts file on each PC on your LAN, and have it point the public hostname being used by a local server to its local private IP address. This does have a disadvantage if you have many portable devices that may be randomly connected to your LAN or to an external network. A more elegant and versatile solution is to disable the DHCP server in the gateway box and run a local DHCP and DNS server on an "always on" local PC; that way portable devices using DHCP would automatically get the local IP address when attached to the LAN, but would get the public IP address when using an external network. The local DNS server route is what I did when I was using the SMC gateway with the NAT Loopback problem (I still use a local DNS server, but now it only provides local hostname (*.dcs-net.lan) resolution and passes public DNS queries to Comcast's DNS servers).

For example if the public hostname for your IP camera web site is mycamera.mydomain.com, and its LAN IP address is 10.0.0.20, then you would need a hosts file with the entry 10.0.0.20 mycamera.mydomain.com (or a DNS "A" record with the same information in a local DNS server).