Free tool · Troubleshooting
MTU & MSS Calculator
Tunnel/encapsulation overhead to the right MSS clamp value.
Cisco MSS clamp
interface Tunnel0
ip tcp adjust-mss 1460
Tunnel overhead figures (IPsec / GRE / VXLAN) are typical values; exact bytes vary with cipher, mode and options. MSS = effective MTU − IP header − 20 (TCP).
About this tool
Free MTU and TCP MSS calculator. Work out the effective path MTU and the TCP MSS to clamp once you add tunnel or encapsulation overhead — GRE, IPsec, VXLAN, PPPoE, 802.1Q and more — with the Cisco ip tcp adjust-mss line ready to copy. Everything runs entirely in your browser — nothing you type is sent to a server.
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