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[Major Hayden <1976526@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

A Fedora user opened an issue[0] about an issue with cloud-init on EC2.
When they launch an instance on a IPv6-enabled subnet, cloud-init sets
the `ipv6.method` to `dhcp` in NetworkManager.

However, AWS uses router advertisements to let instances know about the
nearest router. Using the `ipv6.method: dhcp` setting prevents router
advertisements from working. The instance ends up with an IPv6 address
assigned, but it cannot route traffic.

A workaround is to run NetworkManager commands to fix the issue:

```
nmcli con edit CONNECTION_UUID
nmcli> set ipv6.method auto 
nmcli> save
nmcli> activate
```

The instance immediately routes IPv6 traffic after making that change.
The dhcp setting appears to be applied automatically for EC2 subnets
with IPv6 addresses assigned[1].

I would expect `ipv6.method` to be `auto` in these situations.

Thank you!

[0] https://pagure.io/cloud-sig/issue/382
[1] https://github.com/canonical/cloud-init/blob/53a995e2f852d043d51ad25c1b9afbbe1edafd57/cloudinit/sources/DataSourceEc2.py#L861-L863

** Affects: cloud-init
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1976526

Title:
  IPv6-enabled EC2 subnets always have dhcp enabled

Status in cloud-init:
  New

Bug description:
  A Fedora user opened an issue[0] about an issue with cloud-init on
  EC2. When they launch an instance on a IPv6-enabled subnet, cloud-init
  sets the `ipv6.method` to `dhcp` in NetworkManager.

  However, AWS uses router advertisements to let instances know about
  the nearest router. Using the `ipv6.method: dhcp` setting prevents
  router advertisements from working. The instance ends up with an IPv6
  address assigned, but it cannot route traffic.

  A workaround is to run NetworkManager commands to fix the issue:

  ```
  nmcli con edit CONNECTION_UUID
  nmcli> set ipv6.method auto 
  nmcli> save
  nmcli> activate
  ```

  The instance immediately routes IPv6 traffic after making that change.
  The dhcp setting appears to be applied automatically for EC2 subnets
  with IPv6 addresses assigned[1].

  I would expect `ipv6.method` to be `auto` in these situations.

  Thank you!

  [0] https://pagure.io/cloud-sig/issue/382
  [1] https://github.com/canonical/cloud-init/blob/53a995e2f852d043d51ad25c1b9afbbe1edafd57/cloudinit/sources/DataSourceEc2.py#L861-L863

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