Configuring MTU for VMware HCX Components and Network Profiles

Products

• VMware HCX

Issue/Introduction

This document provides MTU (Maximum Transmission Unit) configuration guidelines for HCX appliances, network profiles, and supporting physical/virtual infrastructure. Proper MTU sizing prevents packet fragmentation, packet drops, performance degradation, and tunnel instability between the HCX Fleet Appliances.

Architecture: Uplink vs. Local LAN Traffic

HCX network traffic falls into two distinct operational categories:

1. Uplink Traffic (WAN Transport Underlay):

• Tunnels established between peer appliances: Interconnect to Interconnect (IX-I to IX-R) and Network Extension to Network Extension (NE-I to NE-R).
• Configurable between 1150 and 9000 bytes in the HCX Uplink Network Profile. The minimum MTU supported is 1150. For detailed uplink specifications, please consult: Network Underlay Minimum Requirements.

2. vSphere Replication, vMotion, Management (Local LAN - same site):

• Review the MTU configuration for the VMkernel interfaces assigned to your Management, Replication, and vMotion networks, and take notes. During the Network Profile configuration, you need to configure the MTU, and the MTU should match the configuration you have. For example, if you have the vmk0 as management with 9000 MTU, configure the HCX Network Profile with 9000 MTU instead of the default 1500, as this might increase replication performance.

Environment

VMware HCX 

VCF Operations HCX

Resolution

The MTU should be configured based on the maximum end-to-end capacity of the underlying infrastructure for both local and uplink (site-to-site) communication.

Example Scenario:

• Local infrastructure (vMotion / replication network) has an MTU of 9000.
• WAN has an MTU of 1600.

In this case:

• The HCX local network profile can have a maximum MTU of 9000.
• The HCX uplink network profile can have a maximum MTU of 1600.

Additional Information

Verification Process

Through the Transport Monitor feature within Transport Analytics, HCX tests and monitors the Path MTU for all Uplink networks across a Service Mesh. Please refer : Understanding HCX Transport Analytics

Alternatively , MTU configuration verification testing can be done through the following CLI commands

CLI Verification Steps

• • Log into your source HCX Manager via SSH.
  • Launch the utility: ccli
  • List the appliances and locate the appliance ID 
  • Run: go <appliance_id>
  • Execute: pmtu

++++++++++ StartTest ++++++++++

---------- Uplink Path MTU [<Source_IX_IP> >>> <Destination_IX_IP>] ----------

1500

---------- Uplink Path MTU [<RSource_IX_IP> <<< <Destination_IX_IP>] ----------

1500

++++++++++ StopTest ++++++++++