I'm facing a frustrating networking issue that started late last Thursday. My regular network consultant is out sick, and I'm hoping for some help here. We have several managed switches in our building, but this problem is isolated to one switch. Some devices connected to this switch are functioning normally, while others are getting valid DHCP addresses but can't communicate on the LAN or the internet. I'm experiencing no response from pings or traceroutes. I've tried rebooting both the switch and the affected devices with no success.
There's an access point connected to the switch that accepts clients, but those clients can't seem to connect to anything. Interestingly, when I plug my laptop into any port on this switch, it works perfectly.
For context:
- The DHCP servers (two Windows 2019 servers) are actively issuing addresses, and I have lease expirations set for 8 days.
- The DHCP range is from 10.0.20.1 to 10.0.21.254, and all devices are within this range, so I suspect there isn't a rogue DHCP server causing the issue.
- Some problematic devices can ping the gateway while others cannot. Any advice would be greatly appreciated!
5 Answers
Have you checked for rogue DHCP servers on your network? Device misconfigurations are sometimes overlooked, and they can cause this sort of trouble. Make sure that there aren't any unsecured devices plugged into the network that could be handing out DHCP addresses.
Good idea! You might want to check the logs on your main DHCP server to see if the clients you're having trouble with show up there.
Double-check your VLAN tags. It's possible that the problematic devices are on a different VLAN. If you've got any rogue DHCP servers around, that could mess things up too.
On a working client and one that isn't, open a command prompt and run ipconfig /all. Compare the results, looking specifically at the subnet mask, default gateway, and DHCP server. Those should match; otherwise, you may have a rogue device responding to DHCP requests. If anything seems off, check your DHCP server settings too. They could be misconfigured, which might explain the communication issues.
I tried that! I can release and renew an IP successfully, getting a valid configuration, yet the communication still fails.
If you can access the problematic switch, verify whether it has connectivity to both malfunctioning clients and other switches. Inspect its ARP table too; something might look off there, especially if the gateway address is within the DHCP range and mistakenly grabbed by a client.
Check the Spanning Tree Protocol (STP) priority on that switch. Sometimes the default settings can lead to issues when there are multiple switches.
Looks like the settings are at their default, but I can send over a link to the current config if it helps.
Is it possible that one of those switches is giving out addresses instead? That could definitely complicate things.