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For my home LAN I use an ASUS RT-N66U running the Asuswrt-Merlin (374.43 LTS) fork which is a nice simple and stable firmware and also updated regularly. My ISP is BT in the UK.

I have been using only IPv4 but decided to switch on IPv6, which BT supports.

The settings that work seem to be straightforward and mostly default:

Connection Type: Native
Interface: PPP
DHCP-PD: enable
MTU: 1492

LAN Options:

Auto Configuration: Stateless
LAN Prefix Length: 64

Enable Router Advertisement: Enable
Enable DHCPv6 Server: Disable

I also used these "Special ISP Options" (the first two are default while the third is not):

Enable IPv6 MTU advertisement: Yes
Release addresses on exit: Yes
Prefix delegation requires address request​: Yes

The issue seems to arise with this last setting.

If I set it to Yes, then I get IPv6 working but my log fills up with these messages - about 1 a second:

dhcp6c: dhcp6c state change detected SOLICIT​

Apart from the log messages, everything else seems to be working. My router doesn't get a global WAN IPv6 address but apparently BT don't provide one anyway. I think maybe that is the cause of the message: my router is requesting a WAN side global address and not getting one.

However, it seems that I do need this setting to get a prefix from BT. If I change the setting to No then the log messages stop but I also lose the IPv6 Gateway and the delegated prefix and, of course, IPv6 stops working.

I can't seem to get IPv6 working without the log filling up (and presumably wasted Solicit messages going out every second).

Any suggestions for what's going on and how to proceed?

Franck Dernoncourt
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strubbly
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1 Answers1

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So, just in case anyone comes to this thread in the future, I seem to finally have a solution.

To get IPv6 working on BT, all the settings are pretty much default except

Prefix delegation requires address request: Yes

That seems to work but also I get the above mentioned log messages - a couple a second. I actually had that running for a long time and just ignored the log - most things seemed to be working. But I finally looked at the log problem again and found what seems to be a more sensible fix which is in the nvram options. It seems I need to disable rapid-commit for dhcp6c client. I don't really know why but that seems to work. So I SSH in and enter

nvram set ipv6_isp_opt=8
nvram commit && reboot

and my log no longer fills up with rubbish. While it's possible I may still have something wrong, I'm getting proper IPv6 on all my clients and the log looks good so I think that's right.

strubbly
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