Mirrored networking intermittently drops forwarding to hypervisor host-only adapter (~30s cycle); Windows-side adapter stays Up, WSL kernel sees link up

Windows Version

10.0.26200.8457

WSL Version

2.7.3.0

Are you using WSL 1 or WSL 2?

• WSL 2
• WSL 1

Kernel Version

6.6.114.1-1

Distro Version

Ubuntu 22.04 and Ubuntu 26.04

Other Software

both VMWare and VirtualBox

Repro Steps

Host-only network on the hypervisor (e.g. VirtualBox 192.168.56.0/24, host .1), guest at 192.168.56.10.
.wslconfig: [wsl2] / networkingMode=mirrored (no other flags).
In WSL, bring up the mirrored host-only adapter (identified by MAC 0a:00:27:*) with 192.168.56.20/24.
ping -i1 192.168.56.10 from WSL — observe periodic ~30s loss waves.
OR - after a reboot observe initial ping goes ok - after 5-10 seconds network goes unreachale and stays so - interface goes DOWN.
ping 192.168.56.10 from Windows (cmd/PowerShell) — stable, no loss, concurrently.

Expected Behavior

Stable connection

Actual Behavior

Windows-side adapter is consistently Up: Get-NetAdapter shows the host-only adapter Status=Up, MediaConnectionState=Connected throughout, including during WSL-side outages. The adapter is not flapping.
WSL kernel sees the interface as up the entire time: dmesg shows no link-down/up, carrier-change, or device add/remove events on the interface during the outages. The only network log is WSL's own CheckConnection reporting getaddrinfo() failed: -5 and connect() failed: 101 (ENETUNREACH) coinciding with each outage — i.e. WSL observes the unreachability but the kernel link state never changes.
Therefore the drop is above the WSL kernel, in the mirror's frame forwarding, not a guest-side link or routing issue.

Already tested:
Reproduces with VirtualBox host-only and, previously, VMware VMnet — not hypervisor-specific.
Reproduces on Ubuntu 22.04 / 26.04 — not distro-specific.
Config-immune: unchanged by firewall=false, removing hostAddressLoopback, removing dnsTunneling; tested with minimal .wslconfig.
Not VBS/HVCI/hypervisor-launch related (VBS Running, hypervisorlaunchtype Auto throughout).
Severity varies per boot (waves vs. early permanent drop), suggesting non-deterministic mirror binding.

The identical configuration is stable on a different machine: a Lenovo ThinkPad with byte-identical software — Windows 10.0.26200.8457, WSL 2.7.3.0, kernel 6.6.114.1-1 — running mirrored mode reaches its host-only VM with no drops. The failing machine is a Samsung Galaxy Book Pro 2 (NP950QED), Intel i7-1260P. Same OS/WSL/kernel, opposite behavior → points to a platform/firmware-dependent path in the mirror's host-only forwarding.
Related issues: Appears related to #10842 (kernel-originated/host-only traffic not reliably mirrored), #13234, #11369.

Diagnostic Logs

Please see attached network log archive from the networking.sh script.

I broughte the interface up, started ping. And after 5 seconds interface went down.
Interface in this case was eth0 but it varies from boot to boot - eth0, eth3, eth5, eth6 etc...

08:13 $ sudo ip addr flush dev eth0
sudo ip addr add 192.168.56.20/24 dev eth0
sudo ip link set eth0 up
ip route get 192.168.56.10
ping -i1 192.168.56.10
[sudo: authenticate] Password:
192.168.56.10 dev eth0 src 192.168.56.20 uid 1000
cache
PING 192.168.56.10 (192.168.56.10) 56(84) bytes of data.
64 bytes from 192.168.56.10: icmp_seq=1 ttl=64 time=2.08 ms
64 bytes from 192.168.56.10: icmp_seq=2 ttl=64 time=1.92 ms
64 bytes from 192.168.56.10: icmp_seq=3 ttl=64 time=1.89 ms
From 80.62.175.69 icmp_seq=9 Destination Net Unreachable
From 80.62.175.69 icmp_seq=10 Destination Net Unreachable
From 80.62.175.69 icmp_seq=19 Destination Net Unreachable
From 80.62.175.69 icmp_seq=20 Destination Net Unreachable
From 80.62.175.69 icmp_seq=21 Destination Net Unreachable
From 80.62.175.69 icmp_seq=29 Destination Net Unreachable

WslLogs-2026-06-09_08-12-45.tar.gz

Begin with the attached networking.sh log archive and reproduce the ~30-second forwarding loss in mirrored mode using the stated .wslconfig and host-only adapter setup. Compare WSL CheckConnection, dmesg, ip route/ping, and Windows adapter state; done means identifying the mirror-side cause and providing stable forwarding, but no source file or test is named.