FRITZ!Box 4020 Service - Knowledge Base
Adjusting the MTU size in the FRITZ!Box
The FRITZ!Box does not allow you to adjust the MTU size manually. This is also not necessary because the FRITZ!Box supports the MSS clamping procedure (Maximum Segment Size) that automatically adjusts the size of data packets being sent to a connected network with a smaller MTU. As a result there will not be any performance losses due to fragmented or discarded data packets.
Note:The Maximum Transmission Unit (MTU) is the maximum size of user data that can be transferred in a single data packet. A maximum MTU of 1500 bytes is available when the FRITZ!Box is used with a cable connection. A maximum MTU of 1492 bytes is available for DSL connections established by the FRITZ!Box using the PPPoE protocol (Point to Point Protocol over Ethernet). The maximum MTU is further reduced by additional protocols used by the Internet service provider.