Over the year’s I’ve had numerous occasions arise when I needed to change the MTU on a Windows based computer. There are a million reasons why this is needed, such as the following.
- Windows Servers deployed in an OpenStack environment require the MTU to be decreased to 1454 in order to work correctly with Neutron.
- DSL very commonly uses a smaller 1492 byte MTU when deployed with PPPoE encapsulation, so performance can be significantly degraded if the router and computers are not decreased to match.
- VPN connections over DSL and some WIFI networks are notorious for failing unless the MTU is adjusted.
What Affect Does MTU Have?
Packet size, also known as MTU or Maximum Transmission Unit, is the largest amount of data that can be transferred in one packet at the physical layer (OSI Layer 1) of the network. Ethernet’s default MTU is 1500 bytes without using Jumbo Frames. For PPPoE the MTU is 1492 and dial-up connections typically used 576 back in the day.
Each transmission unit contains of header and actual data. This data is called the MSS, or Maximum Segment Size. MSS defines the largest segment of TCP data that can be transmitted in a packet. In a more summarized manner,
MTU=MSS + TCP & IP headers.