Q. How do I enable jumbo frames?

A. Windows Vista and Windows Server 2008 introduced jumbo frames support, which enables a much larger Maximum Transmission Unit (MTU) size for data being sent over a network. The larger MTU means more data can be sent before requiring an acknowledgement. Because you send fewer packets for the same data payload, you use less network and computational overhead.

See also: Should I enable jumbo frames on my Failover Cluster networks?

A normal Ethernet frame can be up to 1,518 bytes. This figure includes all the TCP and IP overhead, so the actual amount of data that can be carried is much lower—normally around 500 bytes. This frame size has been around since 10Mbps networks and was designed to minimize the amount of data that had to be resent in the event of network errors, which were very common in the early days (1980s).

Networks today are far more reliable and higher performing. Jumbo Frames allow frame sizes up to 9000 bytes, which means each frame can contain 8KB of data (which just happens to match the NFS datagram size, so with Jumbo frames an entire NFS block can be sent in a single frame).

Most gigabit network equipment supports frame sizes of up to 9,000 bytes, but larger frame sizes are possible. IPv4 uses a 32-bit value for error checking, so the maximum possible frame size using IPv4 is 12KB. IPv6 uses a 64-bit value, so it could allow much larger frame sizes."

Vista and Server 2008 support jumbo frames by default, but most network adapters have jumbo frames disabled. To take advantage of jumbo frames, you need to enable it on your network adapter. The process of enabling it varies based on you network adapter and driver.

Note that when you make the change, the NIC will lose network connectivity for a few seconds. You should also reboot to ensure the change has taken effect.

Learn more: How can I test if two machines are using jumbo frames?

Be aware that most SOHO switches don't support jumbo frames. Additionally, even enterprise switches disable jumbo frames by default and will need to have the feature enabled. I had to disable jumbo frames on my computer because the local switch didn't support jumbo frames and was breaking my communication to the rest of the network—both computers negotiated to use larger frame sizes, but the equipment in the middle couldn't transport it. All of the servers in my main lab connect to my NetGear GS724T, which supports jumbo frames, and so have jumbo frames enabled on their NICs.

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