Docker Desktop 4.92.0: missing IPv6 AF_SPEC and sysctls on tunl0, gre0 and ip_vti0 with network=none

[jonathastorres]

Hello Docker community,

We are investigating IPv6 interface initialization in isolated local containers. This is a question about expected behavior, not a confirmed bug or network leak.

Environment:

• Docker Desktop 4.92.0 (build 240144), macOS on Apple Silicon.
• Docker Engine 29.8.0.
• Reported kernel: 7.0.12-linuxkit.
• Linux ARM64 containers with network=none, read-only root filesystem, non-root user, cap-drop=ALL and no-new-privileges.

Observations:

• In start/end snapshots from two sequential containers, tunl0, gre0 and ip_vti0 have no IPv6 family attributes in AF_SPEC.
• Reading forwarding and force_forwarding under /proc/sys/net/ipv6/conf// returns ENOENT for these three interfaces.
• Their MTUs are 1480, 1476 and 1480 respectively, and all three interfaces are down.
• Other interfaces expose IPv6 controls.
• One container used the default forwarding configuration; the other requested only net.ipv4.ip_forward=0. The IPv6 absences were identical in both.

The embedded configuration extracted from the kernel file distributed with Docker.app has CONFIG_IPV6=y, CONFIG_NET_IPIP=y, CONFIG_NET_IPGRE=y and CONFIG_NET_IPVTI=y. We have not established that this local file is byte-identical to the kernel loaded during the experiment.

SHA-256 of the installed Docker.app/Contents/Resources/linuxkit/kernel file:
3ada07c92ed6e526a91eeb99a4ff5af400e8b6ca51e4c56d3cd0b1ba92b41ba6

Questions:

1. Is this absence expected for these interfaces in a newly created network=none namespace? What initialization or lifecycle mechanism explains it?
2. Where can we find the source revision, patches and build configuration corresponding to this Docker Desktop kernel?
3. Which read-only checks would distinguish expected absence of an inet6_dev object from an initialization problem?

We have not brought interfaces up, changed their MTUs or added addresses. We can provide minimal, reviewed technical extracts if needed.

Thank you for your guidance.