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Missing IPv4 Alongside Present IPv6

New Poster

Missing IPv4 Alongside Present IPv6

Hello,

My problem is defined more in-depth amongst these threads, except with a few minor caveats:

Example 1

Example 2

Example 3

Example 4

 

Specifically - my Internet is working as I type this, as it has worked since I began my venture into Comcast's Xfinity Internet. However, I've purchased new equipment for my LAN and when I try to implement the primary AP / router it becomes messy; no IP(s) received from modem, intermittent local-DNS, botched internal pre-configured routes, and even making my own DHCP inoperable. After many calls to technical support to try to work my way up the ladder, I did manage to talk to someone who could see my problem on their (your) end; however he was ultimately unable to solve anything due to "how the system works," mostly regarding DHCP allocation / provisioning. We tried everything that was mentioned on the aforementioned forum posts, per my request, but the only thing that came of it was an inquiry for a technician. So, as it stands, my modem displays "NONE" under "IPv4 Address" and my new router / gateway displays "0.0.0.0" in its 'ifconfig.'

 

Checking the system log only gives generic messages:

'SYNC Timing Synchronization failure' - 'Loss of sync' / 'Failure to acquire'
'Honoring MDD; IP provisioning mode = IPv6'
'Unrecognized OID'

 

Alas, I wanted to try my luck on these forums because all of these posts have one thing in common: they were solved / fixed / answered in PM's or outside of the public discussion. The forum suggests that we not PM representatives explicitly, so here I am. I do see that @ComcastJohnN is mentioned frequently, amongst many other people that offer troubleshooting advice and general feedback (of which I've followed all to a T). Aside from what has been covered, I've also tried spoofing my verified MAC onto the router to see if it would be able to pass as the device that Comcast's system expects, but that didn't work either. I know for a fact that the MAC attached to my account is the "HFC MAC," which appears to be a common oversight, because it is specifically described as "HFC" on the sticker and on my modem's (MB8600) configuration page.

It truly is a mystery why my old router (RT-AC5300) continues to work with just this IPv6 address, perhaps some kind of tunneling / rerouting / IPv6 to 4 translations? Regardless, I realize there are many ways to incorporate this 'working router' into my setup, but that's something that isn't viable to me for many reasons. Ideally I'm able to utilize the equipment I've invested in.

Thanks for reading.

Official Employee

Re: Missing IPv4 Alongside Present IPv6

Can you summarize what the actual symptoms are that you're experiencing? 

 

One common misunderstanding is that our modems are managed only via IPv6, so when people look at the modem page  and only see  a v6 address, they think their own equipment is not getting a  v4 address, which is not the case. When you boot your modem, the modem itself communicates to management tools using IPv6 only, but the equipment you have connected to the modem--like your router--will get an IPv4 address assigned via DHCP. If you're using  a gateway, which is really just a combination of modem and router, that IPv4 address assignment will be on the gateway. 

 

Another common problem is that people add other devices that act as DHCP servers on their  network. A common culprit is Apple Airport Extreme, but it can be any number of things. When one of  your devices boots up, it sends out a DHCP request for a v4 address and it will use whichever response it receives first. If you have multiple devices handing out v4 addresses, you will have conflicts and some devices will  have the wrong IPv4 information and will not be able to access the internet. You only want one DHCP server on your network..


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New Poster

Re: Missing IPv4 Alongside Present IPv6

Thanks for the prompt reply, John.

My modem is standalone and effectively a bridge. I did not mean to use the term gateway in the sense of a two-in-one. Still, the information you provided in your first paragraph confuses me - is it not the modem receiving the IP(s) and general configuration from Comcast in order to pass it on to my router? My modem is intended to be nothing more than this described 'gateway.'

I'm aware of the conflicts that occur when running more than a single DHCP server without proper configuration; I assure you I'm only running one. My LAN consists of many hosts that are behind a few managed switches (in-wall Ethernet) and / or WLAN access points. Currently, I've a dedicated machine acting as my DHCP and DNS (forwarded) server. I'd like to repurpose this machine and rely on the simplicity of a dedicated router. Therefore, my intentions were to run the AC5300 as some kind of exclusively-managed WLAN AP whilst this router takes its place.

My issue is as follows: the (new) router receives no IP from my modem, despite an attempted reprovision and reformat. However, oddly enough, temporarily putting my (old) router in place of the new one (e.g. between the hosts/APs/switches and my Comcast modem) and power cycling my modem provides the router with an IPv6 address. Your explanation helps me understand why I'm receiving 'mysterious' IPv4 access via an IP that's given to my router (which my modem doesn't seem aware of), but I'm still at a loss for what I need to do to get this effect on my new router. Perhaps there's something in the configuration that I'm unaware of? The first thing I tried was cloning the MAC of my old router onto my new one, and then again to represent the modem. Am I wrong in thinking that these attempts should be a surefire workaround to my issue?

Thanks again for the response.
Official Employee

Re: Missing IPv4 Alongside Present IPv6

If the modem is in bridge mode, it has very little to do with handing out addresses to your equipment. But it does get its own IPv6 address for management purposes. When people go to the modem web admin page  and see only an IPv6 address, they sometimes think that is a problem, but it is not. That has no bearing on the addressing of other network devices. It's only the modem's own IPv6 address.

 

In  your case, it sounds like the wrong HFC MAC was entered into the system when  you got your new modem. That can cause an entry to  get stuck in a backend system that has to be manually cleared out. Until it is cleared out, IPv4 DHCP does not work correctly.

 

Please send me a private message with your HFC MAC (may  also be called CM MAC or CMAC) and I'd be happy to take  a look.


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Official Employees are from multiple teams within Comcast: CARE, Product, Leadership. We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark the post as Best Answer!
Highlighted
New Poster

Re: Missing IPv4 Alongside Present IPv6

I am just posting here because I was told the software for the forums won't allow direct messages until I've made my first post. I seem to be running into the standard issue of having IPv6 but not IPv4 working on my surfboard SB6141, so I'll send the HFC MAC via DM.

New Poster

Re: Missing IPv4 Alongside Present IPv6

@ComcastJohnN
Will you pm me sir. Having the same issues with only being able to access YouTube and google. Nothing else works. Xfinity XB6.
New Poster

Re: Missing IPv4 Alongside Present IPv6

I am having a similar issue. Very few websites work when I'm connected via ethernet cable, but work if I switch to wifi. Can you help me with this? I'm not sure if what to do.