In Zerto 9.0 VRA’s will be able to automatically adjust the Maximum Transmission Unit (MTU) settings based on the capabilities of the underlying network. This helps provide optimal conditions for VRA data transfer between Zerto components.  

Prior to 9.0 

Previously if Zerto seen network fragmentation from the VRA’s users would manually adjust the MTU size on each VRA. This sometimes could be a painstaking task for users having to continually adjust the MTU size and checking the VRA for fragmentation and lost packets.

Another issue was the MTU changes on a VRA didn’t persist through a VRA upgrade or re-install. This meant any adjustments made to a VRA’s MTU configuration must be made again after such an operation. Often this was overlooked when performing a reinstall of a VRA or upgrading to a later release which resulted in replication issues and raising a support call. Zerto’s UI will now alert users of any mismatched MTU data and will provide additional information relating to external factors that may impact VPG’s SLA’s or connectivity.

How does it Work

The VRA will create a connection to the paired site VRA or ZCA without setting a socket Maximum Segment Size (MSS) and if the MTU verification fails an MSS discovery process will be initiated. 

The VRA will continue to reconnect with an MSS value of around 500 bytes and will increase in increments until the socket connection is successful. During this process you will see disconnects and reconnects until the new MSS value is set across all VRA’s. The VRA will save the last valid MSS for each successful MTU verification step and if there is a second failure the VRA will try to reconnect with the last good MSS.

This feature is for Zerto connectivity from it’s Linux components only (VRA to VRA/ZCA) it’s not available from the ZCA back on-premises or Hyper-V at the time this blog was created.