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Unable to receive an IPV6 prefix with DHCP

Frequent Visitor

Unable to receive an IPV6 prefix with DHCP

Until recently, IPv6 was working on my network. My router was able to request and receive a ::/60 prefix via DHCPv6 PD.

 

Recently that's stopped working. My router sends solicitations but there's no response, confirmed via packet capture.

 

DHCPv4 still works.

 

When I attach a different router to my modem, it is able to receive an IPv6 prefix successfully. Normally this would lead me to suspect that my router is at fault, but the packet capture seems to confirm that my router is properly soliciting a prefix and that no response is forthcoming.

 

I tried to contact customer service, but the agent didn't seem to know what DHCP or IPv6 are, and claimed to have escalated my issue but didn't provide any kind of information for me to track that escalation. I never heard anything back after that interaction.

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Contributor

Re: Unable to receive an IPV6 prefix with DHCP

 

What routers are you using?

 

I think I would start by powering off both the modem and router, wait 30 seconds and power on modem first, wait till it normalizes and then power on the router.

 

If that does not work, power cycle the router and if you have a backup of the router when it was working, reload else reenter all of the settings.

Diamond Problem Solver

Re: Unable to receive an IPV6 prefix with DHCP


@Bert-X wrote:

 

 

If that does not work, power cycle the router and if you have a backup of the router when it was working, reload else reenter all of the settings.


OP. FWIW, a simple power cycle operation of the device will not wipe out any customized settings. Only a full reset back to factory defaults does that.

Frequent Visitor

Re: Unable to receive an IPV6 prefix with DHCP

Have tried both reboots and factory resets of both devices (modem and router), no dice.

 

Modem is an SB6121, router is a Mikrotik hAP AC. (The alternate router which was able to get a lease is an Apple Airport Express.)

 

I suspect that I may have some kind of DHCPv6 lease associated with my router, stuck in a bad state in Comcast's systems (this would explain why my backup router is able to get a lease). Unfortunately my router uses a fixed DUID tied to its hardware MAC address and even with a factory reset I can't change that.

Frequent Visitor

Re: Unable to receive an IPV6 prefix with DHCP

Is there nobody who can offer me any advice on this? Two months and still no prefix.

 

I found a very similar thread on the business support forums:

http://forums.businesshelp.comcast.com/t5/IPV6/Suddenly-unable-to-get-a-v6-prefix/m-p/34509

 

It's marked as solved, but unfortunately the solving was all done privately, so it's useless to me, and I can't even reply because I'm not a business customer. It sure sounds like there's just some bad state somewhere in Comcast's systems associated with my DUID, if only I could get ahold of someone who knows how to clear that out.

 

I've tried calling Comcast, but the response was basically "the settings on your modem must be wrong, and since you don't rent it, there's nothing we can do. It's not supported." (false, the modem configuration is controlled by Comcast even though I own it. And my modem is on the list of supported models, and supports IPv6 - and was working perfectly well previously.)

Silver Problem Solver

Re: Unable to receive an IPV6 prefix with DHCP

Can you change the MAC address of the router? Addresses handed out by DHCP are typically based on the Ethernet MAC address the router or gateway presents to the network, not the modem's HFC MAC address. You will need to reboot the modem after changing the router's MAC address.

Frequent Visitor

Re: Unable to receive an IPV6 prefix with DHCP

I have tried changing the MAC address.

 

Unfortunately, on my router, this does not change the DHCPv6 DUID (which is a unique, static ID used instead of the MAC address to identify clients in DHCPv6). It's generated from the MAC address on my router, but once it's generated, it's fixed, and there's no way to change it (changing the MAC address does not change the DUID).

Official Employee

Re: Unable to receive an IPV6 prefix with DHCP

Hi @jdfrench

 

Sorry for the delayed reply. Can you please go into router settings, advanced, and if you have the option, "allow ipv6". This should allow the WAN address of the router to allow ipv6.  

Frequent Visitor

Re: Unable to receive an IPV6 prefix with DHCP

 

Yes, IPv6 is enabled on my router.

 

To go into more detail, my router is running a DHCPv6 client on its WAN interface and attempting to lease an IPv6 prefix, which is typically (part of) what is implied by "enable IPv6". The router is properly sending DHCPv6 'solicit' messages on its WAN interface, with the proper fields set (request prefix, prefix hint of ::/56). It does not receive a response (DHCPv6 'advertise' message).

 

I've double-checked all the settings on the router, including restoring a backup from a time when I'm certain that IPv6 was working normally. The IPv6 firewall is set to allow UDP on port 546 (the port used by DHCPv6 clients).

Official Employee

Re: Unable to receive an IPV6 prefix with DHCP

Ok, thanks for clarifying. Can you please provide your first and last name, the phone number associated with your account, and the MAC address of your modem in a private message? I'd like to review your account and see if I'm able to help fix this.

 

To send a private message click on my name "ComcastChe", then click send a message. 

 

Frequent Visitor

Re: Unable to receive an IPV6 prefix with DHCP

To avoid going silent after taking things to private messages like every IPv6 thread I found while trying to fix this myself:

 

Thanks to Che for taking a look at this! I have a Comcast tech coming by today. If we are able to solve this, I'll post an update here with whatever the issue & fix turn out to be.