ENI and Network-Manager renderers create wrong IPv6 routes

[karibou]

Bug report

When defining IPv6 route in the v2 network config yaml, the IPv6 route is wrongly defined. The Network-Manager renderer adds it to the [ipv4] section.

Steps to reproduce the problem

Using the following network-config :

# cat config.yaml
version: 2
ethernets:
  eth0:
    dhcp4: true
    routes:
      - to: 169.254.42.42/32
        via: 62.210.0.1
      - via: fe80::dc00:ff:fe20:186
        to: ::/0
    addresses:
      - 2001:bc8:1210:232:dc00:ff:fe20:185/64

when creating a Network-Manager configuration using :

cloud-init devel net-convert -p config.yaml -k yaml -d . -D centos -O network-manager

The [ipv4] section has :

[ipv4]
method=auto
may-fail=false
route1=169.254.42.42/32,62.210.0.1
route2=::/0,fe80::dc00:ff:fe20:186

As seen the IPv6 route gets added to the IPv4 section

Environment details

• Cloud-init version: 23.3.1-0ubuntu1~22.04.1
• Operating System Distribution: Ubuntu Jammy
• Cloud provider, platform or installer type: Scaleway

cloud-init logs

No logs are necessary, the behavior can be reproduced at will using the cloud-init command

[TheRealFalcon]

@karibou , thanks for the bug report. I can confirm the problem in versions of cloud-init supporting network-manager.

[karibou]

Hello,
I've been peeking at the code and might have an idea of what is happening.
At line https://github.com/canonical/cloud-init/blob/d0f00bd54649e527d69ad597cbcad6efa8548e58/cloudinit/net/network_manager.py#L256C9-L256C9 we have :

        # Deal with Layer 3 configuration
        for subnet in iface["subnets"]:
            family = "ipv6" if subnet_is_ipv6(subnet) else "ipv4"

            self._set_ip_method(family, subnet["type"])
            if "address" in subnet:
                self._add_address(family, subnet)
            if "gateway" in subnet:
                self.config[family]["gateway"] = subnet["gateway"]

With the data given in config.yaml above we get :

iface["subnets"]
[{'type': 'dhcp4', 'routes': [{'gateway': 'fe80::dc00:ff:fe20:23f0', 'network': '169.254.42.42', 'prefix': 32, 'netmask': '255.255.255.255'}, {'network': '::', 'prefix': 0}]}, {'type': 'static', 'address': '2001:bc8:1210:299:dc00:ff:fe20:23ef', 'prefix': 64, 'routes': []}]

The subnet_is_ipv6 is detecting a family of ipv4. when self._add_route(family,route) is executed, it also adds the route pointed to by gateway even if it is an IPv6 route as an IPv4 route.

It looks like embedding IPv6 gateway in the routes section is not taken into account

[TheRealFalcon]

@karibou , thanks. I'll try to get a fix up soon.

[holmanb]

@karibou , thanks. I'll try to get a fix up soon.

Bah, sorry @TheRealFalcon, I had just started working on this when you grabbed this.

The subnet_is_ipv6 is detecting a family of ipv4. when self._add_route(family,route) is executed, it also adds the route pointed to by gateway even if it is an IPv6 route as an IPv4 route.

Nice evaluation @karibou, that looks to be the issue. I have a wip branch to get this fixed, will try to get this fixed soon.

Aside: subnet_is_ipv6() has no place in net/__init__.py. It belongs to, and should be a part of, the renderer code that it introspects. It is utterly useless without the data structures that it reads from.

[TheRealFalcon]

Just a heads up that I'm going to leave this assigned to me, but I did have another issue come up that takes priority, so if somebody else wants to grab it in the meantime, feel free to comment here. Otherwise, I'll pick it up when I can.

[karibou]

Hello,
Any chance of getting some attention on this issue ? While we have a workaround, it would be nice to have it solved officially.
TIA,
...Louis

[TheRealFalcon]

@karibou , this one hasn't fallen off my radar. I just haven't had the time to get back to it. I'm hoping to get back to it this week.