The default Maximum Transmissible Unit (MTU) for all SDDC networks is 1500 bytes. When you use Direct Connect and a private VIF, you can configure a larger MTU (up to 8900 bytes) on the SDDC uplink if your DX connection supports it.
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 and any SDDC group connections you have configured. Any VPN, whether or not it connects over DX, uses an MTU of 1500, regardless of other settings. To be sure that workload VMs can take advantage of the larger MTU, verify that workload VMs using the DX connection, along with any other interfaces along the workload's connection path, use an MTU that matches the Intranet MTU Value.
All network interfaces on a segment should be set to the same MTU value, or communication problems can occur. Using different MTU values on different segments is generally acceptable, as long as path MTU discovery (PMTUD) is enabled and ICMP traffic is permitted between the networks. If an SDDC group is configured, the Intranet Interface MTU should not be set above 8500 bytes (the maximum supported for SDDC Group traffic). In an SDDC that is part of an SDDC group and also has a DX connection, the maximum usable MTU for all traffic is 8500 bytes, since both the DX private VIF and the SDDC group connection share the same Intranet Interface.
- Log in to VMware Cloud Services at https://vmc.vmware.com.
- Click VIEW DETAILS. , then pick an SDDC card and click
- Click OPEN NSX MANAGER and log in with the NSX Manager Admin User Account shown on the SDDC Settings page. See SDDC Network Administration with NSX Manager.
You can also use the VMware Cloud Console Networking & Security tab for this workflow.
- On the Global Configuration page, click the 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.