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Layer 2 meltdown on Hyper-V connected to Cisco 7941 phone PC port

I have an issues where laptops running Microsoft Hyper-V connect to Cisco 7941 handsets. This is causing no end of problems across the estate including phones registering on the data vlan, phone stuck in reboot cycle, phones not registering in CDP, loss of corporate directory......

Can Cisco equipment work in such a manner? Cisco TAC could not see any issues with versions or configuration on the Cisco equipment.

My understanding is that there should only be one MAC and one IP address associated with the phone's PC port.

The only solutions I can think of are; remove the phones and connect the Hyper-V laptops directly to the switch, or, set the Hyper-V laptop virtual switch to use PAT []

Any assistance or suggestions gratefully received before my network melts down completely.

Hyper-V: Windows 10 & Windows XP

Cisco 7941: 9.4SR

Cisco 3750: 12.2(55)

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This is the Video Over IP community, probably want to try to find similar topic threads in CSC and move to the same area.



if this helps, please rate

I moved this to IP Telephony for now, on behalf of the OP. It may be best-positioned in a Route/Switch community but let's start here.

I suggest starting with a SPAN of a port before/during/after this happening and see exactly what the switch sees. Also, is there evidence of the phone misbehaving? Does the switch log events while this happens (e.g. a port security violation)?

The IP phones aren't supposed to have a switch plugged in behind them due to limited CAM table size but this isn't an unusual configuration, at least not with VMware Workstation/Fusion. I would be surprised if Hyper-V is behaving differently.

Focus on the switch to start: what causes the phone to leave the voice VLAN for example?


Update after XP machines had DHCP removed.

The problem disappeared! No issue with Cisco config and setup it is an issues with XP running on Hyper-V requesting DHCP.

We never managed to capture the fault as it happened, however, giving XP machines a static IP stopped all the symptoms displayed on the Cisco phones and switches.

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