Configuring Frames

The RT-TCP/IP stack can support large packets up to 9 kilobytes. RTX64 jumbo frame sizes are configured with level 3 MTU (IP Maximum Transmission Unit). They don’t include level 1 or lever 2 frame headers. The TCP/IP stack supports Path MTU Discovery. RTX64 devices will successfully communicate over TCP with another device that supports Path MTU Discovery, even if MTUs are configured to different sizes.

NOTE: All tested drivers support Jumbo Packets except the Realtek RtRtl8168 driver. For the complete list of supported and tested drivers and devices, see the RTX64 Supported NICs document available online at http://www.intervalzero.com/technical-support/guides-and-minitutorials/ (RTX64 Documentation tab)

To configure the stack and your NIC cards to use jumbo frames:

  1. Configure the MTU size for the Stack so that it is equal to or greater than the largest MTU value you have specified for any of your individual NIC cards.
  2. Set the MTU value for the individual NIC card so that it is equal to an MTU supported by the card. You can do this through the RTX64 control panel.

NOTE: Maximum frame size is hardware-specific and you should consult your NIC card's hardware documentation for acceptable values.

UDP or ICMP over Fragmented IP

For User Datagram Protocol (UDP) or Internet Control Message Protocol (ICMP) over fragmented IP, if two devices are configured with different MTUs, they can only communicate with IP frame sizes of smaller MTU. In order to run UDP or ICMP over fragmented IP protocol, the IP MTU must be configured to the same number.

Example 1

The Realtek RtRtl8168D/8111D Family PCI-E Gigabit Ethernet NIC Windows driver includes 18 bytes of layer 2 frame header, and FCS in jumbo frame configuration. To run UDP or ICMP over fragmented IP between this driver and any RTX64 interface, you would:

Example 2:

The Intel(R) Gigabit CT Desktop Adapter Windows driver includes 14 bytes of layer 2 frame header in Jumbo Packet size configuration. To run UDP or ICMP over fragmented IP between this driver and any RTX64 interface, you would:

Or

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