Why are jumbo frames not enabled by default

Userlevel 3
I understand that certain WAN connection cannot take jumbo frames, though for the rest of the network , why are they not enabled by default ?
What if any are the disadvantages of having Jumbo frames enabled at at the max MTU size 9216 on all ports on all switches.

2 replies

Userlevel 5

Today there is not a penalty to turning on jumbo frames on all ports, those device that it cannot negotiate a larger MTU it will just negotiate and start talking. My usual base settings for configs are to turn it for all ports all of the time.

Userlevel 3
Enterasys gear has it enabled on all ports bu default as it seems. I don't remember If it is on Extreme gear.