I'm trying to run a personal web service from my lan, on IPv6. I want it to be visible on the public internet, and behind a AAAA record. I need to balance ease of setup, and graceful reconfiguration when the IP prefix from my ISP change.

Which address should I bind to? A local IPv6 address + NAT, or should I embrace globally routable options pushed down to the host via prefix delegation?

My hosts are behind an OpenWRT router, IPv4 + IPv6. OpenWRT gets a /56 prefix delegated by my ISP. I’m using a SLAAC + DHCPv6 combo setup (aka stateless+stateful). The router runs iptables with a layer of config porcelain on top, and for ipv6 only allows wan-to-lan traffic of already-established connections.

I’m willing to give this no-NAT thing on IPv6 a go. I’m okay with punching ports/IPs open in the stateful firewall, but I would like to avoid address translation.

On my stateless+stateful IPv6 setup, my hosts on the lan do autoconfiguration, and also do DHCPv6 to get addresses on a ULA prefix (fd00:cafe::), so they get the following set of addresses:

fd00:cafe::4/128                    # ULA local (by dhclient -6)
2001:2:3:4:a8a8:efcf:d96d:1315/64   # slaac+privacy global
2001:2:3:4:22f:bcff:fe12:1234/64    # slaac+EUI64 (macaddr)
fd00:cafe::a8a8:efcf:d96d:1315/64   # slaac+privacy local
fd00:cafe::22f:bcff:fe12:1234/64    # slaac+EUI64 (macaddr)
fe80::21f:bcff:fe08:c07a/64         # link local

The 2001:2:3:4: addresses are routable on the public internet. The fd00:cafe:: are routable only locally on my subnet (ULA). The fe80: of course isn't routable.

The v6 IP I pick for my service will have to end up in an AAAA DNS record somewhere, so it would be preferable if it didn't change every hour or so.

• The prefix delegated by my ISP doesn't seem to change, ever, until I reboot the router. So the globally routable prefix is usable with a little bit of dyndns goop.
• The slaac+EUI addresses say a bit about my mac address, and I don't like that.
• The slaac+privacy addresses are privacy-preserving, but rotate every few half-hours, and that is less desirable. Addresses stick around if they are still in use, but they would be released everytime I started the service (and dns would need to be updated).
• Another option is to just statically pick a suffix I like for my service (e.g. ::d00d), with the same globally routable prefix and statically assign that to my nic, like so:

$ sudo ip -6 addr add 2001:2:3:4::d00d/64 dev eth0

(NOTE: I’m using OpenWRT, and I haven’t found a way to add a dynamic DHCP lease reservation for something like this (i.e. take global prefix, and slap "d00d" at the end). So static configuration on the host is perhaps necessary. )

Then in my applications, I could bind to that address only.

# ./myserver -l 2001:2:3:4::d00d/64 -p 8080

Now, once I’ve got a listening socket bound to a publically routable IP on the host, what's the best way to inform the router to let the SYN packets flow in for it? I need a hole punched here. UPnP, NAT-pmp?

Am I thinking about this the wrong way around? What’s the typical setup on IPv6?

Update

I changed /etc/config/dhcp on my router to specify a hostid suffix for a dhcp reservation, and restarted odhcpd. I was hoping I would receive an extra IPv6 with the wan prefix and my chosen suffix, but no luck. The dhcp6 client on my host still doesn't receive that extra IP. Probably related to this odhcpd issue 61.