The default Maximum Transmissible Unit (MTU) for all SDDC networks is 1500 bytes. When you use Direct Connect, you can specify a larger MTU for the traffic it carries.

You can enable DX to use a larger MTU when you create the VIF. If you do this, you'll also need to open the NSX Global Configuration page and set a higher Intranet MTU Value.

This larger (or Jumbo) MTU value applies only to DX connections over a private VIF. Any VPN, whether or not it connects over DX, uses an MTU of 1500, regardless of other settings. You should also verify that the interface MTU of workload VMs that use the DX connection is set to a value that matches the Intranet MTU Value. Otherwise, workload VMs won't be able to take advantage of the larger MTU.

Procedure

  1. Log in to VMware Cloud Services at https://vmc.vmware.com.
  2. Click Inventory > SDDCs, then pick an SDDC card and click VIEW DETAILS.
  3. Click OPEN NSX MANAGER and log in with the NSX Manager Admin User Account shown on the SDDC Settings page.
    You can also use the VMC Console Networking & Security tab for this workflow. See SDDC Network Administration with NSX Manager.
  4. On the Global Configuration page, click the pencil icon (pencil icon), set a higher MTU value in the Intranet Uplink field, then click SAVE.
    The value you set must be less than or equal to the smallest MTU value for all your DX virtual interfaces. In practice this means that you should set all your VIFs to the same MTU value (the default, at 1500 or Jumbo, at 9001), since having any VIF that does not support a Jumbo MTU effectively limits all DX connections to an MTU of 1500. Mixing MTU sizes within a network can lead to packet fragmentation and other problems that result in poor network performance.
    Note:

    To leave room for Geneve (Generic Network Virtualization Encapsulation) headers, the SDDC intranet MTU is capped at 8900 bytes to avoid packet fragmentation at the VIF.