Alpine container statefull IPv6 => no IP assigned

Incus
, ,
1

Hello,

are there any known gotchas with Alpine containers not retrieving any IPv6 address on a stateful DHCP setup?

I assigned the provided public IPv6/64 network to incusbr0 and configured statefull DHCP for website hosting etc. (IPv4 is backup for now and private IP)

config:
  ipv4.address: 123.123.123.1/24
  ipv4.dhcp.ranges: 123.123.123.20-123.123.123.254
  ipv4.nat: "true"
  ipv6.address: 2a01:aaaa:bbbb:cccc::1/64
  ipv6.dhcp.stateful: "true"
  ipv6.nat: "false"
  ....

Spinning up any Ubuntu or Debian container and assign a static IPv4 or IPv6 works without any issues. Can ping the gateway,host, internet out of the container and I can ping the container from my homenetwork. In short all working properly.

However, if I launch any Alpine container they only get an IPv4 assigned but no IPv6 regardless if I assign an address or leave it empty on Incus config. The only way to get IPv6 working in Alpine is to edit /etc/network/interfaces like this:

auto eth0
iface eth0 inet dhcp
iface eth0 inet6 static
    address 2a01:aaaa:bbbb:cccc::123/64
    gateway 2a01:aaaa:bbbb:cccc::1
hostname $(hostname)

After restarting the network IPv6 stack works like IPv4. Container can reach internet and it can be pinged from the outside world.

Incus version is 6.14 and host OS Debian 12.

Any inputs or thoughts are welcome…

2

Sounds like Alpine doesn’t have a dhcp6 client - or maybe you need to install something extra to get it?

I presume you already tried

iface eth0 inet6 dhcp

?

3

I tried multiple different ways by looking at their docs, finding block posts, etc.

Kind of tried this first beside all the other options found.

Just taken another approach and came across this link Enable IPv6 DHCP by default although 5 years old it seems it still works:

apk add dhclient

cat <<EOF >> /etc/network/interfaces

iface eth0 inet6 manual
  post-up dhclient -6 eth0
EOF

/etc/init.d/networking restart

Results into a proper IPv6 config dynamic or static configured in Incus.

Based on the linked post IPv6 implementation in udhcpc is rather incomplete (used by Alpine). I’m pretty sure Incus or better DNSMasq does the right thing as other distros are working properly.

Think this note is key:

In summary, while udhcpc can be used for IPv6, its reliance on Router Advertisements for address assignment can lead to unstable IPv6 addresses. For more stable and manageable IPv6 networks, consider using a dedicated DHCPv6 server and client.

Not sure if there is an option to use “Router Advertisements” with Incus and if this would solve the real issue?

Would prefer a native solution but can live with the approach above. Not sure if I can call it solved.

4

(Aside: that link you gave doesn’t work for me. It says “Error: access denied: denied by administrative rule”. It thinks I’m an AI bot, although I’m just browsing from Firefox or Chrome with no plugins worth mentioning, definitely no Javascript blocking)

The most direct way to prove this would be: install Alpine as a VM, manually, using their supplied ISO image. If it can’t pick up an address via dhcp6 then it’s an issue with Alpine and nothing to do with Incus. You could then take it up with them directly.

If on the other hand dhcp6 client does work in the VM, then you can work out what’s different between that and the container/VM images on images.linuxcontainers.org.

5

Cut and paste from google, properly only works using direct google link? Search for “alpine dhcp6 client” and it came up under top 5 links. Sometimes you are able to click it only through goole.

Right, given all the things I read about it I kind of think this is an Alpine issue. Will try the ISO approach during the next days.

What I noticed, the default /etc/network/interfaces doesn’t contain anything about IPv6 which makes me believe there is no IPv6 support on default but might be mistaken.

6

I found it. Your link has some trailing stuff ?__goaway_challenge=...etc - if I strip all that off, it works.

7

Great you found it. Here is another link to look at https://gitlab.alpinelinux.org/alpine/aports/-/issues/?sort=created_date&state=opened&search=ipv6&first_page_size=20

It kind of points all in direction of Busybox missing some implementation details?
At least I’m not alone is having IPv6 issues :wink:

8

What about just using SLAAC? works great here.

9

Are you using stateful IPv6 or just the default setting?
What version of Incus are you on?
Did you make any network changes to your Alpine container

10

I will admit I’m using macvlan, and simply getting the slaac router solicitations from my isps router. Router. I don’t have any need for an internal Network. Since these machines are on the internet.

Sincerely,

THOMAS MUNN