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NetFixer
Bah Humbug
Premium
join:2004-06-24
The Boro
Reviews:
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2 edits

[IPv6] IPv6 problems with router's factory MAC address

At 0:dark:thirty this morning, I was doing some equipment shuffling that required me to temporarily disconnect my D-Link DIR655 router. It appeared to survive the disconnect and it reported that it was back online after it was reconnected. However, I did notice that its network IPv6 PD prefix had changed from 2601:5:C80:90::/64 to 2601:5:C80:A0::/60 as shown in the two screen shots below.


Old



New


With the new 2601:5:C80:A0::/60 PD prefix, my outbound IPv6 connectivity terminated at the DIR655's LAN, but I could do pings to IPv6 hosts on the Internet from the DIR655's internal ping test page. Connected PCs were receiving an IPv6 address in the 2601:5:C80:A1::/64 range, but they could not get traffic past the router's LAN. The DIR655 did however respond to IPv6 pings on its LAN using both the local and Internet IP addresses. The router's IPv4 WAN address did not change, and IPv4 connectivity was not effected.

I tried everything I could think of to get IPv6 connectivity back again:

Disabling and re-enabling the DIR655's IPv6 firewall made no difference.

Factory default reset on the DIR655, and minimal manual config didn't help.

Factory default reset on the DIR655, reverting the firmware to the 2.03 level mentioned in the Comcast documentation at »mydeviceinfo.comcast.net/?homega ··· egateway followed by minimal manual config didn't help either.

I also tried using Comcast's 6to4 tunnel instead of native IPv6, with similar negative results.

All of the above things were tried with the DIR655 isolated from my network with only a single notebook PC attached, so there was no interaction with anything on my network. During this time, I reverted my network to use my old Netgear WNR1000v2-VC, and neither it nor devices behind it had problems with native IPv6 connectivity.

Finally, in desperation, I cloned the DIR655's WAN MAC with the MAC address from a retired D-Link DVG5102s VoIP ATA (because I have seen MAC cloning fix weird Comcast network/routing problems). After doing that, my IPv4 IP address changed as expected (previously that had not changed), and my network IPv6 PD prefix changed to 2601:5:C80:84::/64 as shown below.


Cloned


With the cloned MAC address, everything works as expected (and I was also to upgrade back to the latest 2.10 firmware release), but if I change back to the original factory MAC address (which had previously been working just fine), the IPv6 problem returns.

This post is primarily just a "heads up" to anyone who might suddenly find their IPv6 connection no longer works (even though the parameters seem to be correct). I am not necessarily looking for help, since I consider the cloned MAC address to be a "fix" (although it should not be required). I will however work with any Comcast tech who wants to do a postmortem to find out why it is happening.

FWIW, while the culprit might seem to be the "/60" PD assignment, I previously have received "/60" PD assignments on this router (it is totally random whether I get a "/60" or a "/64"...it happens with no changes on my end) and did not experience any problems because of it.
--
A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed.

When governments fear people, there is liberty. When the people fear the government, there is tyranny.

voiptalk

join:2010-04-10
Gainesville, VA
It may be a SWAG, but what makes sense is ....

The /60 that initially caused the problem was not being properly inserted into the CMTS and traffic was unable to route back to you.

Changing the MAC also changed the DUID. That gave you a new PD assignment that was routing properly.

When you changed it back, the old DUID re-appeared and you got the bad addressing back.

So, it's not really the MAC address, per se. But, the DUID value that is derived from it.

Thoughts?


NetFixer
Bah Humbug
Premium
join:2004-06-24
The Boro
Reviews:
·Vonage
·Comcast Business..
·Cingular Wireless
said by voiptalk:

It may be a SWAG, but what makes sense is ....

The /60 that initially caused the problem was not being properly inserted into the CMTS and traffic was unable to route back to you.

Changing the MAC also changed the DUID. That gave you a new PD assignment that was routing properly.

When you changed it back, the old DUID re-appeared and you got the bad addressing back.

So, it's not really the MAC address, per se. But, the DUID value that is derived from it.

Thoughts?

True enough with regards to what happened after I cloned a different MAC address into the DIR655's WAN, but the problem occurred with absolutely no changes to the DIR655 on my end. All I did was to power cycle the DIR655 (something that I have literally done 100's of times previously with no problems getting a usable IPv6 connection). There was no reason for the DUID to to have changed (and looking at the saved logs, I don't see where it changed until I cloned the MAC address), or for Comcast to arbitrarily change the PD prefix (or its allocation length).

Here are syslog excerpts showing the last refresh for the PD prefix 2601:5:c80:90::/64 assignment, the first occurrence of the PD prefix 2601:5:c80:a0::/60 assignment, and the assignment of the PD prefix 2601:5:c80:84::/64 for your enjoyment (or for anyone else who is curious):





--
A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed.

When governments fear people, there is liberty. When the people fear the government, there is tyranny.


NetFixer
Bah Humbug
Premium
join:2004-06-24
The Boro
Reviews:
·Vonage
·Comcast Business..
·Cingular Wireless
reply to NetFixer
After reading NetDog See Profile's post »Re: [IPv6] Comcast IPv6 Address Assignment/Delegation I tried using the DIR655's factory MAC address again, and now it gets a 2601:5:c80:8e::/64 PD prefix, and IPv6 works OK again with the factory MAC address. Apparently, I got caught in the middle of the CMTS config changes.



--
A well-regulated militia, being necessary to the security of a free State, the right of the people to keep and bear arms shall not be infringed.

When governments fear people, there is liberty. When the people fear the government, there is tyranny.