This grid configures the various options of the network cards in the Untangle server.
MTU is the maximum transmission unit. Usually the correct configuration is Auto, which in most cases is 1500. Occasionally if the MTU is lower and PMTU (Path MTU discovery) is broken, it may be necessary to lower the MTU manually to a lower value. No settings (blank) is "Auto" - any other setting is an explicit hardcoded MTU.
The Ethernet Media dropdown configures the duplex of the Network card. Usually Auto is the correct value, however some network cards do not properly automatically configured the duplex setting or perform poorly when Auto is configured. In those cases you can manually configure the speed and duplex setting.