Troubleshooting VM Network Connectivity Issues in VMware

 🚦 Troubleshooting VM Network Connectivity Issues in VMware 🚦

When a virtual machine suddenly loses network connectivity, it’s not always obvious where the problem lies — it could be the VM itself, the vSwitch, uplinks, VLANs, or even the physical switch.

Here’s a step-by-step flow you can follow to quickly isolate and resolve the issue:

🔎 Troubleshooting Process

1️⃣ Validate Port Group & vSwitch

✔ Ensure the VM’s network adapter is connected to the right port group.

✔ Port group name must exist and be spelled correctly.

2️⃣ Check VM Network Adapter & OS Settings

✔ Verify NIC is connected.

✔ Confirm guest OS has the right IP/DNS/Gateway.

✔ Run basic ping/traceroute tests.

3️⃣ Verify Physical NICs (pNICs) & Uplinks

✔ Use esxtop → n to check which pNIC the VM is mapped to.

✔ Shut down physical switch ports one by one to detect uplink misconfigurations.

✔ Use netdbg vswitch instance list to identify active uplinks.

4️⃣ Validate VLAN Configuration

✔ Ensure VLAN ID on the port group matches the switchport configuration.

✔ Switchports must allow tagged VLAN traffic.

5️⃣ Check NIC Teaming / LACP

✔ If using EtherChannel or LACP, verify correct configs on both ESXi and physical switches.

✔ Test by toggling uplinks one at a time.

6️⃣ Advanced Checks

✔ For Jumbo Frames (MTU 9000), ensure consistency across VM, vSwitch, and switchports.

✔ Rule out hidden NICs (especially in P2V-converted VMs).

✔ Confirm no storage or CPU contention causing freezes.

⚠️ Note: ESXi does not log VM-to-VM traffic failures (beyond port/link errors). Always troubleshoot while the issue is occurring to pinpoint the root cause.

✅ By following this process, you can systematically narrow down the problem and restore VM connectivity with confidence.