port forwarding stopped working

Our router is set up to provide addresses on the local network using DHCP, in a range starting at 10.1.10.150. We have some servers on the local network that have fixed IP addresses *below* that range. We set up port forwarding (using non-common port numbers) to provide external access to those servers.

This has worked flawlessly for some years now. A few days ago, it stopped working. Port testing tools would show the port(s) in question to be closed.

We contacted Comcast and a support technician had us lower the DHCP range (down to 10.1.10.2) to include the servers, even though they have fixed IP addresses, and that seems to work. We confirmed it yesterday by setting it back to 10.1.10.150 (broken), and 10.1.10.2 (fixed).

Why is this suddenly necessary? No one in our organization changed the router in any way. And also, the documentation (https://business.comcast.com/help-and-support/internet/comcast-business-ip-gateway-static-firewall/) says:

"If the IP address of the local server PC is assigned by DHCP, it may change when the PC is restarted. To avoid this, you can assign a static, private IP address to your server by manually configuring the server’s IP settings. Be sure that the assigned IP is outside the range of DHCP addresses set on the Comcast Gateway but in the same subnet as the rest of your LAN".

I'm nervous to leave it this way, it seems like if we add a server and forget to give it a fixed address, might it get one vis DHCP that collides with one of the existing servers?

Responses

Comcast_JamesC

Official Employee

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41 Messages

3 years ago

Greetings, @fred_ross_perry! Thanks so much for taking a moment out of your busy day to leave a post on our community forum. I'm sorry to hear you're having issues with your network settings, but you have definitely come to the right place for assistance.

I'm unable to tell from your description alone why you would suddenly need to change your DCHP range, but if you could send our team a private message with your full name, business name, and the service address associated with your account, I'd be more than happy to look into this for you.

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fred_ross_perry

New Contributor

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5 Messages

3 years ago

Not sure how to address a PM to your team, plz advise...

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Comcast_JamesC

Official Employee

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41 Messages

My apologies for not explaining the process, but it may have recently changed, and I wasn't sure which option was currently available. Regardless, to send a Private Message, please click on the chat icon in the top-right corner of the screen, next to the bell icon, and then type or select "Xfinity Support" to initiate a live chat. The old option was to select "Comcast Business" or simply "Business", and that one may still be available as well, depending on when you set up your account. Regardless, please let me know if you encounter any issues. I look forward to speaking with you about this.

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3 years ago

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JohnK626

New Contributor

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1 Message

3 years ago

Same problem for me... port forwarding suddenly stopped working after working fine for over 2 years. Cisco DPC3941B router, DOCSIS Software Version 2.3.10.13_5.5.0.5, Software Image Name DPC3941B_4.8p9s3_PROD_sey. Fixed in similar manner as described above.

To get around this:

1. Under Gateway->Initial Setup, change the DCHP address range to include your machines with fixed ip addresses.

2. Under Connected Devices->Devices make certain your fixed ip address server is set up as a device entry with a fixed ip address and not DHCP or no entry as mine was previously. I am hoping this second step prevents the router from assigned that ip address to another box if the server is turned off.

The frustrating parts...

1. There was no notification of this router configuration change.

2. I spent more than an hour playing with the port forwarding, deleting and trying to recreate entries, only to get vague messages that there was something wrong with the data entered and that it didn't get saved... and then finding that it DID get saved but with empty entries for port and IPV4 address. AT LEAST FIX THE ERROR MESSAGE AND GIVE THE PEOPLE THAT DISCOVER THIS PROBLEM A HOPE OF SOLVING IT!

3. I've been involved in networking (including writing network transports) for what feels like forever (over 30 years) and have always configured DHCP for a separate range from my fixed IP addresses... I don't know why someone would insist on an overlap for their port forwarding to work. It would never have occurred to me had I not tripped across this post!

THANK YOU FRED!

And someone please tell Cisco to clean up their software!

John K.

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fred_ross_perry

New Contributor

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5 Messages

3 years ago

Thanks @JohnK626 . I have the same router model and software that you do.

There was apparently a planned outage on July 9th at 2:09am, which is likely when the software update happened.

I tried to find out some details about the updated software version, to no avail.

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iatinc

New Contributor

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9 Messages

3 years ago

This "fix" worked for me too but it's so gay. Wondering what will happen after the next power outage when the all the machines using DHCP restart in random order, competing with static-ip servers for the same IPs...

As it is, the surprise update broke our web orders and alienated hundreds of customers for more than half a day.

Tier 1 rep clueless and told me that our (unchanged) port forwarding config would never work, despite that it has for years until exactly when the FW update hit. Funny, she was arguing that port forwarding cannot do exactly what its purpose is.

(edited)

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