But if he was on the Spurs we wouldn ' t have Kawhi <| sep |> We must consider your question from two perspectives Layer 2 and Layer 3 . Layer 2 All members of the same Layer 2 domain subnetVLAN must share the same MTU . Fragmentation is a Layer 3 feature , and not a Layer 2 feature . It cannot be reliably predicted as to the result of a large MTU host sending to a defaultMTU host . It might work , and it might be dropped . Layer 3 The router must have correct MTU sizes for each segment , or nothing is going to work as expected . Some applications do not like having their data packets fragmented DF bit . We don ' t know what applications are in your environment . Devices with Fast Ethernet interfaces rather than Gigabit have very little to do with the discussion of MTU size . As uanothersackofmeat says , 1015 % increase is about all you should expect . Changing the MTU values as you describe should not have such a dramatic impact on throughput . If you are observing that level of performance increase , something else was broken and enabling Jumbo frames is masking it , or otherwise fixed that in addition to changing to larger packet sizes . Try updating all of your NIC drivers . Lastly , specific to LAN gear In some LAN equipment , the maximum Frame Size allowed in a Layer 2 VLAN is a separate configuration from the Layer 3 interface MTU . Increasing the Layer 2 Jumbo Frame value , without increasing the Layer 3 MTU value is generally harmless . But as said above , if you ' re going to enable largeMTU , everything in the subnet should match . Otherwise strange things will happen . Don ' t turn things on that you don ' t understand .