Finding Ring Buffer Size and MTU for Virtual Machine Network Interfaces

Products

• VMware vCenter Server

Issue/Introduction

This article describes the procedures for determining the ring buffer size for a specific virtual machine's network interface and finding the Maximum Transmission Unit (MTU) configured on the associated ESXi virtual switch.

Environment

VMware ESXi

Resolution

1. Finding the VM Interface Ring Buffer Size

The ring buffer size is found by first identifying the virtual machine's port number and switch name, and then querying the ESXi network configuration using vsish.

1. Identify the ESXi Host and Log In: Determine the ESXi host on which the target virtual machine (VMNAME) is running and log in to that host using SSH or KVM with root privileges.

2. Find Port and Switch Details: Run the net-stats command to find the <PortNumber> and <Switch Name> associated with the VM's network interface (e.g., VMNAME.eth0).

   • Command: net-stats -l | grep -i VMNAME

   • Example Output Format: <PortNumber> 5 9 <Switch Name> <MAC Address> VMNAME.eth0

3. Check Ring Buffer Stats: Use the vsish command, substituting the actual <Switch Name> and <PortNumber> obtained in the previous step, to view the ring buffer summary. The command below specifically targets the size of the "1st ring" buffer.

   • Command: vsish -e get /net/portsets/<Switch Name>/ports/<PortNumber>/vmxnet3/rxSummary | grep "1st ring"

 

2. Finding the Virtual Switch MTU

The MTU (Maximum Transmission Unit) is a switch-specific setting, not a per-VM setting. It is applied universally to all ports on that virtual switch.

1. Run MTU Check Command: Use the esxcfg-vswitch command to list the virtual switch configurations, which includes the configured MTU for each switch.

   • Command: esxcfg-vswitch -l

Additional Information

Reference link: https://knowledge.broadcom.com/external/article/324556/large-packet-loss-in-the-guest-os-using.html