WSL2 can't receive jumbo frames when using a VPN with a 9000 MTU and mirrored network.

[oldshensheep]

Windows Version

Microsoft Windows [Version 10.0.26100.712]

WSL Version

2.2.4.0

Are you using WSL 1 or WSL 2?

• WSL 2
• WSL 1

Kernel Version

5.15.153.1

Distro Version

ArchLinux

Other Software

No response

Repro Steps

1. Connect to a VPN with 9000 MTU
2. In WSL, ping -s2000 1.1.1.1

Expected Behavior

can ping

Actual Behavior

PING 1.1.1.1 (1.1.1.1) 2000(2028) bytes of data.
^C
--- 1.1.1.1 ping statistics ---
26 packets transmitted, 0 received, 100% packet loss, time 26019ms

Actually, it does get reply:

Diagnostic Logs

No response

[github-actions]

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View similar issues

Please view the issues below to see if they solve your problem, and if the issue describes your problem please consider closing this one and thumbs upping the other issue to help us prioritize it!

Open similar issues:

• WSL2: Jumbo frames are not forwarded to mirrored interface on Linux (#11046), similarity score: 0.81
• Unable to access VPN from WSL2 when networking mode set to mirrored (#11072), similarity score: 0.76
• openvpn connection stops working after upgraded to 2.0.9 with mirrored networking (#10879), similarity score: 0.74

Closed similar issues:

• ping breaks when using experimental.networkingMode=mirrored and a VPN (#10805), similarity score: 0.76
• Unable to use VPN routes from within WSL 2 (#7315), similarity score: 0.72

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[oldshensheep]

I have conducted some experiments:

With MTU 1500:

> curl http://google.com --trace - -L
Successfully received a 301 redirect to www.google.com and downloaded.

With MTU 9000:

> curl http://google.com --trace - -L
Successfully received a 301 redirect but failed to download.

If you use Wireshark, you will observe that all jumbo packets are being ignored. This is why the TCP connection is successfully established, and the HTTP 301 response (825B) can be received, but the webpage from 'www.google.com' (which consists of multiple packets, with the largest being 8203B) cannot be fetched.

If you are using a VPN with an MTU of 9000 and cannot change the VPN configuration, there is a workaround:

Choose the right interface:

> ip a 
...

then

> ip link set dev <interface_name> mtu 1500"

[oldshensheep]

I found similar issue.

VPN issue.
#11361 (comment)

not VPN, but with a 9000 MTU eth0
#11027

and the bot listed.
#11046

[Ghost-LZW]

Confirmed, the similar issue #11361 is caused by the 9000 MTU setting. the workaround set mtu to 1500 work.

[ghost]

/dupe #11046

[microsoft-github-policy-service]

Hi! We've identified this issue as a duplicate of another one that already exists in this repository. This specific instance is being closed in favor of tracking the concern over on the referenced thread.

Thanks for your report!