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I have a Windows XP (SP3) Hyper-V guest with a Windows 11 host and am observing that certain egress traffic from the guest is seemingly not reaching the host. Specifically, while a TCP active open from the host succeeds (ie., SYN, SYN-ACK), subsequent egress from the guest for this flow is not received on the host.

Wireshark screenshot

10.0.0.1 - Host
10.0.0.3 - Guest

In this test I’m using FTP on the guest, since as it entails an unsolicited message (the hello), of which is missing, further suggesting it’s guest->host related only. Note that ICMP bidrectional is functional.

  • Firewalls are disabled on both host/guest.
  • Localhost test (guest) shows the service is functional.
  • The Hyper-V switch type is Internal
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I’ll answer my own question here for the sake of others: as somewhat expected, the problem was related to paravirtualization optimizations and/or in junction with guest offload. I didn’t bother narrowing down the precise culprit(s), however simply disabling all ‘acceleration’ features in the HyperV guest’s network settings, along with the usual NIC offload features in the guest solved the problem.

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Thanks for following up with the answer. :slight_smile:

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