broken IPv6 on Debian

[WhiteRabbit-Code]

Latest google-guest-agent 1:20241011.01-g1 on Debian 12 breaks IPv6 connectivity by creating an interface file which misses the inet6 configuration:

$ cat /run/network/interfaces.d/ens4 
auto ens4
allow-hotplug ens4

iface ens4 inet dhcp

Since I'm IPv6 only, this broke my whole infrastructure.

Reverting back to the latest version 20211116.00-6+b7 from the Debian repositories creates a correct interface file and immediately restores IPv6 connectivity:

$ cat /run/network/interfaces.d/ens4 
auto ens4
allow-hotplug ens4

iface ens4 inet dhcp
iface ens4 inet6 auto

Please do not neglect IPv6 as this is the default in today's Internet.

[drewhli]

Can you share reproduction steps for this issue as well as the image you were using when you encountered this issue?

[gaughen]

@WhiteRabbit-Code just checking in to see if you're still seeing an issue, if yes, would you please share reproduction steps?

[WhiteRabbit-Code]

Sorry for the late reply. I've created a VPC with a dualstack subnet, so it got a public IPv6 range assigned. Back then, the VM was created within this subnet and immediately got assigned a public IPv6 address.

The image is a debian-10-buster-v20210420 but has been continuously upgraded via sudo apt-get update && sudo apt-get dist-upgrade to currently Debian 12.8.

During this update process, one day google-guest-agent 1:20241011.01-g1 was installed and the IPv6 address got removed.

[ChaitanyaKulkarni28]

@WhiteRabbit-Code 20211116.00 is very old guest-agent version and we no longer support it.

I just verified again running on dual stack instance, I see IP getting assigned.

$ apt list --installed | grep google-guest

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

google-guest-agent/google-compute-engine-bookworm-stable,now 1:20241011.01-g1 amd64 [installed]

$ curl -L "http://169.254.169.254/computeMetadata/v1/instance/image" -H "Metadata-Flavor: Google"
projects/debian-cloud/global/images/debian-12-bookworm-v20241112

Running ip a or netplan status shows IPv6 address. I would suggest trying 20241011.01 on Debian-12 directly it should work fine.

However, to highlight fundamental change that went into guest-agent is it no longer relies only on dhclient as its being deprecated and uses default network manager available in OS, netplan in this case.

Previous version of agent would launch dhclient -6 for primary NIC and current version does not manage primary nic unless explicitly configured to. Refer this for more details on it.

But by default OS/netplan should configure it based on /etc/netplan/90-default.yaml.