MTU & MSS calculator
Pick the link MTU and stack the encapsulations from the outside in. You get the MTU left for the inner IP packet, the TCP MSS to clamp to and the ping commands to prove it.
Link
Examples
Packet anatomy
One full-size packet on the link, outermost header first. Headers are drawn wider than their share so they stay visible; the byte counts are exact.
Layer by layer
| Layer | Overhead | Inner |
|---|
IPsec overhead depends on the inner packet size because ESP pads to the cipher block; the inner figure is the largest packet that fits.