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IPv6 support for hostfwd + guestfwd

Currently, hostfwd does only forward IPv4 traffic. It's not possible to specify an IPv6 address.

There has been a patchset around. I'm not sure why it hasn't been merged yet. Latest incarnation: https://www.mail-archive.com/qemu-devel@nongnu.org/msg814483.html

Host environment

  • Operating system: nixos-unstable
  • OS/kernel version: Linux 6.12.18 #1-NixOS SMP PREEMPT_DYNAMIC Fri Mar 7 17:25:47 UTC 2025 x86_64 GNU/Linux
  • Architecture: x86-64
  • QEMU flavor: qemu-system-x86_64
  • QEMU version: master (1dae461a)
  • QEMU command line: 
    qemu-system-x86_64 -M q35 -m 4096 -enable-kvm -hda Arch-Linux-x86_64-basic.qcow2 \
                   -net nic,netdev=user.0,model=virtio \
                   -netdev user,id=user.0,hostfwd=tcp::52022-:22

Emulated/Virtualized environment

  • Operating system: Arch Linux
  • OS/kernel version: Linux archlinux 6.13.7-arch1-1 #1 SMP PREEMPT_DYNAMIC Thu, 13 Mar 2025 18:12:00 +0000 x86_64 GNU/Linux
  • Architecture: x86-64

Description of problem

When using hostfwd, only IPv4 connections are forwarded.

Steps to reproduce

  1. Start vm with the aforementioned command using a system image that comes with a socket listening on both IPv4 and IPv6. (I used Arch Linux Box which comes with sshd enabled by default).
  2. Connect to the forwarded socket:
  • IPv4 succeeds:
    • ssh -oPasswordAuthentication=yes arch@127.0.0.1 -p 52022
    • nc -zv 127.0.0.1 52022
  • IPv6 does not:
    • ssh -oPasswordAuthentication=yes arch@::1 -p 52022
    • nc -zv ::1 52022

Additional information

Patches

Other times requested

Edited by Frédéric
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