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[dougjensen]

Like millions of other households, I (have to) use Comcast Xfinity for internet (and other) service. The router is part of their cable box, and there is no user way AFAIK to do things like port forwarding. So unless there is some work-around that is not mentioned in the MC25 documentation, it seems I cannot access my PC-resident media with another device (smartphone, tablet, laptop).

[wer]

What you can do is buy your own router.

https://www.xfinity.com/support/articles/list-of-approved-cable-modems

[hoyt]

Are you sure you have no access?  I had Comcast, but had my own modem - it's the right move to avoid the $7 monthly rental fee, when you can buy a modem and router for less than that within a few months.  However, with AT&T they supply a modem with no monthly rental fee, and I have to use it, but I can still access it.  With a different ISP before, same thing. 

https://howchoo.com/g/mwiyywixmgz/how-to-log-in-to-a-comcast-xfinity-router

[dougjensen]

My Comcast Xfinity service is Internet (both wired and Wi-Fi), TV with voice control, and telephone. The Xfinity interface box connects to the residence cable wiring. One cable modem was supplied and I added another of my choice (after confirming compatibility with my service speed). Comcast tells me that there is no marketplace alternative device (unsurprisingly).

[dtc]

There are several articles on xfinity's website about port forwarding.

https://www.xfinity.com/support/articles/xfi-port-forwarding

https://forums.xfinity.com/t5/Internet/ANSWERED-How-to-set-up-Port-Forwarding-on-your-Comcast-modem/ta-p/3030290

[dougjensen]

Thank you. The referenced instructions do not work for me--for example, I am unable to access my Xfinity cable box IP address. I called Comcast tech support and was told that my cable box--which provides VOIP and smart television (including Netflix, Amazon Prime, You Tube, etc.) as well as wired and WiFi Internet--does not allow user access for things such as port forwarding. Since this is a weekend, I believe I got a lowest level tech support person who may not know the correct answer, so I will call again Monday during normal business hours to see if I get a different answer.

[dtc]

Did you try accessing through your user account also?

If you really have no access to such features, you may need a different service/model.  This works with normal X1 xfinity modems.  Maybe it is the VOIP.  If so, maybe a separate VOIP phone would make sense.

[dougjensen]

I did try by accessing it through my user account. The cable box is not a modem, it is a lot more functional than that (as you note regarding VOIP), although I do use two modems in conjunction with it to get Ethernet connections for the Internet. Without the modems the box provides only Wi-Fi Internet access. My residence is in a community which allows only Comcast Xfinity for not only Internet but also for VOIP telephone and TV. No other TV, telephone, and Internet services and equipment are allowed.

[wer]

If you provided the model of cable box you have, people might be able to give better guidance.  There will be a label on it somewhere.

It's an all in one device, yes?  DVR, phone, Wifi, router, channel guide all in one box?

[hoyt]

Thank you. The referenced instructions do not work for me--for example, I am unable to access my Xfinity cable box IP address. I called Comcast tech support and was told that my cable box--which provides VOIP and smart television (including Netflix, Amazon Prime, You Tube, etc.) as well as wired and WiFi Internet--does not allow user access for things such as port forwarding. Since this is a weekend, I believe I got a lowest level tech support person who may not know the correct answer, so I will call again Monday during normal business hours to see if I get a different answer.

I think I'm understanding that your network is like this:

Coax Cable > Comcast supplied box > Your own router (wifi, etc)

Is that correct?  What gives you your IP?  Your router or the box from Comcast?

If it's your router, you likely need to plug directly into the Comcast box to access the IP noted in the online guides.  You said it only provides wifi, but it has to at least have one ethernet connection, because I think that's what you said your router is plugged into? 

With my AT&T service that's what I have (Fiber > AT&T box (that's capable of providing VOIP) > my Router).  I had to access the AT&T box to turn enable a DMZ done.  The IP that I needed to access was 192.168.0.1, but once I was assigned an IP from my own router, it wouldn't resolve that address.    So I needed to get an IP from the AT&T box, by plugging directly into it, and then accessing the IP.  Once in there I could enable DMZ (or whatever they called it).  At that point, you tell the provided box to send all commands to a certain IP, mac address or ethernet port (your router).  Then your router is able to take over the actual routing capabilities that you want.

[hoyt]

... although I do use two modems ...

Can you explain this part?  Do you mean two routers?  Or a router and a switch perhaps?

[dougjensen]

@wer: Sorry for the delay on the model number. I don't have that yet (long story) but meanwhile I discovered that the cable box is two boxes, a bigger one with the channel display facing into the room, and a slightly smaller one that appears to be the Wi-Fi box.

@hoyt: Thank you for that information. I have a main cable box with an auxiliary Wi-Fi box, the main box is connected to Comcast by a cable that enters my residence underground from outside. The main cable box provides cable service (Internet, TV, VOIP) throughout my residence. I have two PCs that each have a standard off-the-shelf Motorola cable modem to RJ45 for Internet access; and I have one PC and multiple phones and tablets that use the Wi-Fi service for Internet access. My IP's come from Comcast via the main box or the Wi-Fi box.

[hoyt]

@wer: Sorry for the delay on the model number. I don't have that yet (long story) but meanwhile I discovered that the cable box is two boxes, a bigger one with the channel display facing into the room, and a slightly smaller one that appears to be the Wi-Fi box.

@hoyt: Thank you for that information. I have a main cable box with an auxiliary Wi-Fi box, the main box is connected to Comcast by a cable that enters my residence underground from outside. The main cable box provides cable service (Internet, TV, VOIP) throughout my residence. I have two PCs that each have a standard off-the-shelf Motorola cable modem to RJ45 for Internet access; and I have one PC and multiple phones and tablets that use the Wi-Fi service for Internet access. My IP's come from Comcast via the main box or the Wi-Fi box.

What do your motorola boxes plug into (the other end, not the RJ45 to the PC)?  The 'main cable box'?  And the MC instance that you're trying to access is on one of those two computers?  I'm asking because you're calling these modems, which would indicate that they operate as a different network.  If these are actually modems, then you'll need to access your computer by leaving your wifi network, and accessing this hard wired network.  In that case, you need to access the motorola setup page to open port access.  That seems strange though, so I'm wondering if this isn't really what you mean?

I don't have Comcast anymore, but I seem to recall if I signed into the webpage it would tell me the model of the modem that I had.  If you go to my.xfinity.com and sign in, there should be a Devices section under the internet choices, which will list that out.

[dougjensen]

@hoyt: One of the PCs is connected to a Comcast-provided CISCO DPC3941T data/voice modem which provides an RJ45 jack for the Internet and also provides an RJ11 connector for VOIP telephone service at the desk where that PC is. My personally owned Motorola (data only) cable modem for the second PC connects to a male F connector in a wall (there are numerous such F connectors mounted in the walls throughout the building). A TV is also connected to one of those connectors. The cable in the walls throughout the building connects to the Xfinity "set top box" (as Comcast calls it on my account page, without a model number). The third PC (a laptop) connects to the Internet through the Wi-Fi provided by the Wi-Fi box that is connected to the set top box. Smartphones and tablets also use Wi-Fi. The set top box connects to a Comcast cable that is brought in underground from outside. The MC instance I want to use would be on the PC connected by the Motorola cable box to the building's cable. I hope this is clearer.

[BradATIMA]

Do the computers connected to the Cisco modem and the Motorola modem have the same external IP address or do they have different external IP addresses? Does a device connected via WiFi have the same or different external IP address? Going to a site like https://www.whatsmyip.org/ on each computer will show you the external IP address for that machine.