PC Unable to obtain IP address

[alfa aficionado]

Really stumped on this one...

My PC is unable to obtain a valid IP address since switching to a Ubiquiti system, comprising an USG, 48 port switch and a single AC-Pro wireless access point. (The LAN port of the USG is connected into the switch) The PC is connected via Ethernet (wired Cat6 network) - it doesn’t have a wireless adapter. DHCP is turned on in the USG and all other “wired” devices have been allocated valid IP addresses.

Everything else is able to access the internet - this single PC is the only device that can’t. I have tried connecting it to different ports at the switch (I even have 2 separate network points in the room) but it makes no difference.

I am able to ping 127.0.0.1 without any issues, suggesting that the PC’s network card is working. I have tried disabling IPv6, flushing the DNS cache, even the ‘Network Reset” option in Windows but nothing has worked.

I’m not sure where to go from here and would appreciate any suggestions?

Edited by alfa aficionado on Wednesday 19th June 23:38

Edited by alfa aficionado on Wednesday 19th June 23:38

[scottri]

Network card drivers up to date?

[thebraketester]

Silly question. Is the cable good?

[alfa aficionado]

scottri said:

Network card drivers up to date?

Yeah

[alfa aficionado]

thebraketester said:

Silly question. Is the cable good?

Yeah - tried different cable (& different network socket too, which would have been wired separately) but same result. I’m baffled by this one...

[ging84]

127.0.0.1 is localhost, it never touches the physical interface so definitely does not mean the network card works.

[Mr E]

Run wireshark.
Capture from Eth0.
Filter for “bootp”

You should see a “discover, offer, request, ack” sequence.

[megaphone]

The PC is set to obtain an address via DHCP? Did you use it to set anything up? Did you give it a static IP?

Edited by megaphone on Thursday 20th June 07:59

[Baldchap]

Having checked for manual settings and the device being active in device manager, I'd lob a cable tester on either end, at least that way you can 100% eliminate dodgy cable.

Failing that I'd take the client home and see if it connects there.

Edit: Mac address isn't bound to anything silly or blocked?

Edited by Baldchap on Thursday 20th June 08:10

My money is on a dodgy NIC.

Edited by Baldchap on Thursday 20th June 08:10

[gavsdavs]

When you plug a cable into an ethernet card, the link state light should come on (this is before the interface in the OS gets an IP address).

Have you eyeballed the nic and the corresponding switchport to see if you get a link light ?

What else is connected to the switch ? Can you switch over to a different/known working switchport?

[oilslick]

Is your DHCP pool full? I remember having a router years ago where the DHCP pool came out of the factory with a 5 device limit configured and devices 6+ weren't allocated an IP address. Set it to 50 and then everything was better.

[LordGrover]

Have you tried setting static IP in the correct range?

[P4ulB]

Presumably there is still a router in the mix here connected to the USG. If so, could DHCP be running on that also - so 2 DHCP servers on the same network.

Guessing a Windows based PC here. If so, go to a command prompt and type IPCONFIG /ALL and see what it comes back with.

[h0b0]

P4ulB said:

Presumably there is still a router in the mix here connected to the USG. If so, could DHCP be running on that also - so 2 DHCP servers on the same network.

This would be my guess as well. I fell in to the same trap when upgrading my network. Most devices were fine but Sonos was not happy. Identify the 2 DHCP servers and disable one and it should resolve your issue.