Tunnel problems caused by IPv6 Router Advertisements from bog-standard PlusNet router
Now here's a thing. Anyone using an IPv6 tunnel might want to watch out for this.
I've just noticed my bog-standard PlusNet router is sending IPv6 Router Advertisements to my internal network. At the moment the RAs are not doing anything useful, they are missing any prefix settings.
I don't know when it started. I've been a very happy HE IPv6 tunnel user for several years, and it has been so reliable I don't check it on any regular basis. It just happened that today I noticed one of my laptops had only a link-local address, no routable address. It took a while to work out what was going on.
I'm not on the IPv6 trial, and never have been. I'm just a standard PlusNet customer, on FTTC.
So it looks like maybe PlusNet are Doing Stuff to prepare IPv6 for the masses.
In case it helps anyone, I see my router (the usual Technicolor Gateway) has some new firmware from when I last checked: 10.2.5.2.FO. The web interface has changed quite a bit from when I last looked.
The RAs look like this:
#
# radvd configuration generated by radvdump 1.9.1
# based on Router Advertisement from fe80::a6b1:e9ff:fe7b:3400
# received by interface p2p1
#
interface p2p1
{
AdvSendAdvert on;
# Note: {Min,Max}RtrAdvInterval cannot be obtained with radvdump
AdvManagedFlag off;
AdvOtherConfigFlag on;
AdvReachableTime 0;
AdvRetransTimer 0;
AdvCurHopLimit 64;
AdvDefaultLifetime 0;
AdvHomeAgentFlag off;
AdvDefaultPreference medium;
AdvSourceLLAddress on;
}; # End of interface definition
Now I'll have to work out what to do about it: I'm not keen on my IPv6 becoming unreliable. 
@sdfranks wrote:
I've just noticed my bog-standard PlusNet router is sending IPv6 Router Advertisements to my internal network.
That's naughty
Now I'll have to work out what to do about it:
One obvious solution is to ditch the cheap rubbish most ISPs supply and use a decent router. The only reason I'm still using the PN supplied one at home is I haven't had the time to sort out my IT stuff and roll my own (having left a lot of it still running at my parents' house.)
Or just turn off IPv6 in the router and see if that stops the RAs.
In any case, you are allowing an external third party to mess with your router (firmware updates & settings change) ? I always turn off stuff like that.
But I suspect your are being a bit optimistic suggesting it's them getting ready for IPv6 rollout. From following what has and hasn't been said here, it's clear they aren't treating this as a high priority, and there's no indication that anything might be imminent. More likely is that the manufacturer has cooked a new firmware version and they've just rolled it out to all users - or at least all those who haven't disabled it. It's likely that the new firmware just coincidentally has different IPv6 settings/behaviour - sending out RAs (it is a router after all) but without any prefix(es) as there's no IPv6 delegation from the ISP. In the target market, sending RAs even if you don't have anything to offer won't break anything - those of us using tunnels etc aren't the target market for these devices 
All fair points, especially about being overly-optimistic. I really ought to know better.
Like you, I tend to replace the ISP-supplied router; but I've just never had any need since I got FTTC. Perhaps until now, anyway.
Actually it is handy that PlusNet has kept my router up-to-date on firmware, it saved me having to do it. And to be fair to them, all my customisation has remained intact, including odd stuff that is only possible using the command-line interface.
Thanks for your comments.