VM network has dropped transmit packets

Products

• VMware NSX

Issue/Introduction

Dropped VM network packets can be caused by network congestion, hardware issues, software bugs, or configuration problems. To troubleshoot, check for overloaded queues, update drivers and firmware, monitor host resources, and analyze traffic with network monitoring tools. 

Environment

ESXi
NSX-T

Cause

Common causes

Network congestion: The most frequent cause, where a network or switch queue is full and drops incoming packets. 

Hardware problems: Issues with physical network interface cards (NICs), cables, or switch ports on the host. 

Software or configuration issues: Outdated drivers, firmware, software bugs, or incorrect network configurations can all cause packet loss. 

Overloaded devices: A host might drop packets if it doesn't have enough CPU or memory resources to handle the workload. 

Resource contention: In a virtualized environment, VMs can compete for host resources, leading to dropped packets if one VM is consuming too many. 

Resolution

How to troubleshoot

Check host resources: Ensure the ESXi or other host running the VMs has sufficient CPU, memory, and network resources. 

Update drivers and firmware: Make sure all network drivers and firmware are up to date on both the VMs and the physical hosts. 

Monitor network traffic: Use monitoring tools to capture and analyze network traffic between affected VMs to look for patterns or anomalies. 

Investigate the data path: Use tools like traceflow to examine the path packets take and identify where drops are occurring, whether at the virtual switch, physical NIC, or a downstream switch. 

Test with different configurations: Try moving a VM to a different host or creating a new VM on a different host to see if the problem is isolated to a specific VM or host. 

Check physical connections: Inspect cables and switch ports for any signs of damage or loose connections.