If you receive the following error when downloading to a SymNet Express unit over IP you may need to increase the MTU (maximum transmission unit) settings associated with your computer’s NIC (network interface card):

Download failed: Failed to download configuration on Ring #1, Address #1.

If your MTU settings are not large enough you will not be able to download over IP, though upload may still be possible.  Serial communication will not be affected.

MTU is the largest protocol data unit in bytes that can pass onwards.  SymNet will require an MTU setting of at least 1492.

To check your current MTU setting:

Start > Run > open: cmd

From the command prompt window type:
netsh interface ipv4 show subinterfaces

This will show the network interfaces on your computer and the packet size (MTU) limitation.  Make note of the MTU value and name of your Local Area Connection.

To change the MTU type:
netsh interface ipv4 set subinterface “Local Area Connection” mtu=nnnn store=persistent

where
Local Area Connection is the name of the network connection on your computer connected to SymNet.

nnnn is the desired value for MTU.