In all resources seen that tackle the term of "jumbo frame", I understand that it is applied in a LAN, because:
- It's a Jumbo frame, and a frame is for Layer 2
- These resources talk a lot about switches (L2), and the scenario when they didn't support the jumbo frame.
But I came across this information:
If there is within the network, a switch incompatible with Jumbo frame, it will either drop the frame, or fragment it
The fragmentation is a layer 3 function, how come that a switch can do fragmentation ?
Update: adding the resources that cause confusion (to me) about the use of jumbo frame by the routers, and the application of fragmentation by the switches
Starting by the most informative resource, the answer of Alex Maison. As mentionned under the section "Key Point #1":
For a large frame to be transmitted intact from end to end, every component on the path must support that frame size. This means that the switch(es), router(s), and NIC(s) from one end to the other must all support the same size of jumbo frame transmission for a successful jumbo frame communication session.
As I know, the jumbo frame can be used only within the LAN, but he mentions the word "router" !! same thing later under section "Key Point #3"
For a jumbo packet to pass through a router, both the ingress and egress interfaces must support the larger packet size. Otherwise, the packets will be dropped or fragmented.
This lead me to wonder if a jumbo frame can go out of the LAN ?
Hereafter other resources regarding the misunderstanding / misuse of the word "fragmentation" with the switch:
- Ref 2, see "3. What are the drawbacks of jumbo frames?" section (the last paragraph)
- Ref 3, see the answer before the last one (andrew.burns' answer)