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MTU calculator
Stack encapsulation overheads to find the effective path MTU and the TCP MSS to clamp to. Runs entirely in your browser — no project or account is required.
Path
Base MTU1500 for Ethernet, 9000 for jumbo frames.
Effective MTU1496
Overhead−4B
TCP MSS1456IPv4
TCP MSS1436IPv6
Path MTU is below 1500 — ensure PMTUD works or clamp TCP MSS, or large packets will black-hole.
Applied overheads
| Encapsulation | Bytes |
|---|---|
| 802.1Q VLAN tag | −4 |