FRITZ!Box 3390 – Service - Knowledge Base
Manually adjusting the MTU size for DSL connections
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 to the smaller MTU of connected networks. This prevents 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. The maximum MTU for DSL connections established via PPPoE (Point to Point Protocol over Ethernet) is 1492 bytes. The internet provider can reduce the MTU by using additional protocols.