Tuesday, August 17, 2021

Ethernet not getting IP at office after using VPN at home

Hi folks,

Really helping someone can shed some insight on what's going on as I've run out of ideas...

Situation:

Multiple devices failing to get DHCP lease via ethernet from the corporate network, wifi works fine

Learned info thus far:

Devices know their is a connection (laptops show up when I do 'show mac address-table' on the switch) but it's a 169.x.y.z ip address and Windows says 'Unknown network, no internet connection (public network)' for the network icon.

I thought it was a problem with the switch as all the problematic devices are plugged into the same bank on the same switch (41, 43, 45 & 47). All ports are configured the same way, just like any other data port on that switch.

What I was told as I was leaving which changed things a lot was that they were working fine before the users took them home and connected to their home network using ethernet and connected their work VPN. Since then, while in the office, the ethernet hasn't worked (both the onboard ethernet and the ethernet port on the dock).

Things tried:

nuke the tcpip stack

rebuild the port on the switch (Cisco Catalyst 9000 series I think from memory)

disable/enable NIC

remove the NIC and reinstall

firmware/driver updates (Dell Lattitude 5510's if anyone is interested)

set static ip (can't even ping the default gateway)

swapped cabling

different device plugged into the port

I didn't have an opportunity to try them in another switch port as it's full populated and I couldn't exactly kick a working device off and risk breaking it also (as unlikely as that may be).

I'm leaning towards some broken routing or oddball security policy which has been deployed, like mac security on a switch but from Windows. I can't, however, find anything that's actually wrong when I go down this route.



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