To comply with RFC 1122, TCP/IP uses a maximum transmission unit (MTU) of 536. This is used to avoid fragmentation of a datagram by intermediate gateways along the path.

The RFC-recommended MTU size is used by default. You can use the TCP/IP Option command with the USERFCMTU option to turn off the default. You can then specify a larger MTU size.

On systems using MCP v3 Networking, USERFCMTU is disabled by default. The default MTU size is the size configured for your interface. Typically, the MTU size on a system running MCP v3 Networking is 1500.