My ISP gives me a unique /128 IPv6 address


My ISP gives me a unique /128 IPv6 address, which is happily and expectedly taken by OpenWRT.

Usually an ISP gives at least a /64, thus one can connect more computers than ever dreamed of...

But what can I do of a /128 while keeping OpenWRT front?
Can it be bridged somehow (to my Linux PC)?
Or do I have to connect directly the PC to the ISP modem? (bypassing OpenWRT)

Thanks a lot.


Thanks for the prompt reply. Very active and great support (as usual).

It looks like quite a heavy setup, but that's a solution, at least. (Didn't know that package even existed!)
I'll try a couple other things first
(TBH our OpenWRT router works so well currently, I'll install the package and setup only it if it is really necessary)

Thanks again.

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Talk to your ISP and your local regulator, in IPv6 at the very least the whole final 64bit are considered to be the interface identifier and are supposed to be under control of the endsystems. Actually the recommendation is to assign a /48 or a /56 to each end customer site, so that subnets can be created there. A/128 is something useful for a infrastructure supplier that uses say, a router and only ever needs a single rather permanent address. So this might be a simple oversight of your ISP.


I'm in Japan ...........

Does your ISP advertise the IPv6 address over PPPoE tunnel or using DHCP?

P.S. I don't know how things work in Japan but you should definitely tell your ISP to give you at least a /60 of global unicast IPv6 addresses.

DHCPv6 from the router.

How does it work in Japan?
You want to cry? Or laugh, depending? On my side, that was crying.

So I need an IPv6 connection to test some servers configuration, from the comfort of my home office.

First, I try the fixed fiber connection.
My OpenWrt is v6 configured but has never seen an IPv6 around.
So I call the ISP who says that I need to fill a form to get IPv6 ; that'll take a few days, the IPv6 allocation is case-by-case... and there is no guarantee I might get one, depending on my location in Japan.
I was a bit intrigued (and worried) about the "get one", but... so be it.

Then try IPv6 from the phone company
I was a bit in a hurry, so I try with my phone provider ; my iPhone v11 knows how to deal with v6.
I call the support, they have to call me back because it's a pretty tecky matter. Sure.
Finally, I get to talk to someone tech-savvy who says...
"Actually, we cannot provide IPv6 right now, because we tend to stop supporting it...".

Back to the fixed fiber ISP
The location is ok, the support calls me to setup IPv6...
I need to switch off the modem, and switch it back on... They say to my surprise "you get one IPv6"...
So I checked OpenWrt: I indeed got a /128.

  • me: what do you want me to do with that? I don't work directly from the router...
  • them: actually you have to disconnect the router and plug the PC directly to the modem...

After a good hour of discussion, citing Iljitsch van Beijnum in his excellent IPv6 book (p.20),
"everyone gets a /48 unless they are absolutely, positively, never going to need more than a single subnet, in which case they get a /64".
So they said they're going to change the infrastructure, and by next March (2022), it'll be better...

NB1: the ISP has been assigned a /32 by JPNIC/APNIC in 2004...
NB2: changing of phone provider tomorrow

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You could grab a free /64 and /48 from if your ISP won't give you any more than a /128 .