FRITZ!Box 6590 Cable 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 be no 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 using the FRITZ!Box with a cable connection. This value may then be further reduced by additional connection protocols used by the Internet service provider.