New computers can't connect to the network

Question

Good Morning,

We have a business environment in which we have 3 Cisco 3850 PoE stacked and We manage our DHCP through our DC server.

Last weekend our UPS had a failure and switched off all outputs, so all the equipment has been reset since then.

On Monday I started noticing that first, I lost ping to a card reader that had been working fine until now. And sencond and most important: every new computer we plug into our network resolves DHCP fine but has no ping to our GW.

So here's what I know:

DHCP requests go through just fine, I can see the new computer's records in our DHCP server.
Ping works fine to other computers in the same Vlan/subnet, but I get 0 response from the Gateway
With wireshark I could see that these computers spam ARP packets asking for our Gateway with 0 response
I flushed my own ARP cache and I actually got a response from the ARP request first try
If I use an USB network card from another computer that was already working, it works no problem, until today for some reason
The MAC table in the switch has been flushed already
Wi-Fi works OK, we have it on a different Vlan but similar setup with the same DHCP server.

Any ideas? I googled the hell out of it and I found no one with the same issue.

Thanks in advance!

Is the DHCP scope handing out the address for the Gateway to new machines? — Davidw, Jul 30 '18 at 14:17
Aside from the card reader, are computers other than the new computers affected? — Davidw, Jul 31 '18 at 07:07
Nope, only things that hasn't been on the network in some time — Arheisel, Jul 31 '18 at 20:15
Are they all in the same vlan, or are multiple vlans involved? — Davidw, Jul 31 '18 at 21:26
For now it looks like there's only one vlan affected, except for the card reader that could be unrelated. — Arheisel, Aug 02 '18 at 19:41
So it sounds like it's either not responding to unknown/unfamiliar MAC addresses, or that VLAN. — Davidw, Aug 04 '18 at 01:00
It may be that changes were made on the router and never saved. If the router is not responding, you should edit your question to include the router configuration. — Ron Maupin, Aug 10 '18 at 03:22
Side note: that's why you connect one PSU of the switches and machines to the UPS and the second directly to the power grid. — Gerald Schneider, Aug 10 '18 at 05:11

score 0 · Answer 1 · answered Aug 10 '18 at 03:15

0

We had what sounds like the same issue. Drove us crazy for 3 months. Turned out it was some sort of fast networking setting in the bios

answered Aug 10 '18 at 03:15

Robert Cotterman

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2

Any update on the situation? – Robert Cotterman Sep 03 '18 at 02:27
Sadly, no. For all I can say it stopped on it's own, but priorities shifted after a short while and we never looked at the issue again. Turns out the switches lost a small change on the power cycle, but that only solved the card reader problem that ended up being a wrong Vlan. – Arheisel Sep 12 '18 at 12:40

New computers can't connect to the network

1 Answers1