CentOS - May 2022 - IPv6 token with /60 and prefix delegation

I'm trying to figure out how to assign a "static" address that 
automatically sets the prefix to what the ISP delegates. It seemed like the 
token system would accomplish that, but reading the kernel source code, 
I've discovered that tokens only work with a /64 delegation. My ISP offers 
a /60, so the token is ignored and I get a random address, instead.

Is there some way to use prefix delegation to pick a /64 from the /60 and 
loop it back onto the same interface to make it use the token? Or is this 
/64 restriction actually a kernel bug?

See line 2788 here, where the token is ignored if the prefix isn't /64:

<https://elixir.bootlin.com/linux/latest/source/net/ipv6/addrconf.c>

Am I reading the code wrong? It looks like all the autoconf stuff that 
computes interface addresses breaks with smaller prefixes.

On 5/8/22 05:00, Kenneth Porter wrote:
> I'm trying to figure out how to assign a "static" address
that
> automatically sets the prefix to what the ISP delegates. It seemed like 
> the token system would accomplish that, but reading the kernel source 
> code, I've discovered that tokens only work with a /64 delegation. My 
> ISP offers a /60, so the token is ignored and I get a random address, 
> instead.
> 
> Is there some way to use prefix delegation to pick a /64 from the /60 
> and loop it back onto the same interface to make it use the token? Or is 
> this /64 restriction actually a kernel bug?
So right now, you're assigning a /60 address to your LAN interface?  If
so, you almost certainly shouldn't do that.  Instead, you should (as you
say) pick a /64 from within the delegated /60 and use that subnet.  (The
other /64 subnets within the /60 can be used for other VLANs.)

The details of doing this are going to be dependent on what software
you're using to manage the network - NetworkManager, ISC DHCP client,
etc.

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