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MTU Calculator

Compute effective MTU after tunnel and encapsulation overheads.

Overheads
Effective MTU1492 B
NoteFits standard Ethernet frame

How to read the result

Effective MTU = base MTU − sum of overhead bytes. Oversized packets fragment or drop if DF is set.

Example

1500 − PPPoE 8 → 1492

FAQ

Why does PPPoE use 1492?

PPPoE adds 8 bytes, so 1500 − 8 = 1492 is the largest unfragmented payload.

What if result is too small?

Below 68 bytes is invalid for IPv4; reduce stacked tunnels or raise the base MTU (jumbo frames).