hyperv vswitch promiscuous mode

Question

Hi all,

In hyper-v server 2022 datacenter i have setup a small lab to perform to test an application before i migrate it from vmware esxi. i am trying to replay a PCAP from one VM to another via tcpreplay. The two VMs are connected with each other via a virtual switch with Private Networking and enabled MAC spoofing.

The problem is that some initial packets are sent, but then the traffic stops.

 

After an investigation, we have come to the conclusion that it has to do with the MAC addresses present in the PCAP. Below is an example of the MAC addresses:

 

MAC1 -> MAC2 : SENT

MAC1 -> MAC3 : SENT

MAC3 -> MAC1 : NOT SENT

 

If we edit the PCAP so that the source MAC is always “MAC1” and destination MAC is always “MAC2”, all of the packets are sent.

 

What could be causing the above problem? Can we somehow configure the switch to ignore the MAC addresses?

 

Kind Regards,

Aris Zografos

Answer 1

Hi Aristeidis Zografos,

Hope you're doing well.

1. Ensure that the source and destination MAC addresses of all packets are correct and match the MAC addresses of the current virtual machine. You can use the tcprewrite tool to modify the MAC address in the PCAP file.
2. Check the configuration of the virtual switch to ensure that it allows all the necessary MAC addresses and that there are no security policies enabled that could cause traffic disruptions.
3. In a test environment, you can try to assign static MAC addresses to the virtual machines and ensure that these addresses are properly referenced in the PCAP file. This avoids conflicts caused by dynamically generated MAC addresses.
4. When using tcpreplay, you can try adjusting the parameters to ensure that the packets are played back correctly.

Best Regards,

Ian Xue

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