~ path tools

MTU / MSS Calculator

MTU / MSS Calculator helps plan packet sizes when tunnels or access technologies add overhead. It is useful when fragmentation or black-hole MTU problems are suspected.

What It Calculates

• Effective MTU after overhead.
• Recommended TCP MSS.
• Common overhead profiles for PPPoE, GRE, IPsec, and VPN paths.
• Custom overhead values for unusual designs.

When It Helps

Use it when large downloads stall, VPN apps behave oddly, SIP/TLS sessions fail through tunnels, or a firewall needs MSS clamping values.

Notes

• MTU issues can be asymmetric.
• ICMP blocking can hide path MTU discovery problems.
• Pair with Ping and MTR for practical testing.