FREE TOOLS / MTU-MSS CALCULATOR
MTU / MSS Calculator
Calculate physical Maximum Transmission Unit (MTU) and TCP Maximum Segment Size (MSS) sizes based on encapsulation (GRE, PPPoE, IPsec, VXLAN) overheads.
Security and Privacy Note:
This tool runs in your browser for preliminary assessment and calculation purposes. Data entered here is not sent to the server, stored or logged. Use sample or masked data instead of real production IP plans, hostname lists, configuration files or confidential network information. Results are not a design, security or resilience guarantee.
Why is MTU / MSS Crucial?
Incorrect MTU and MSS settings lead to packet drops, sluggish performance, or site accessibility failures (black hole routers). Best practices:
- IPsec, GRE, or VXLAN tunnels reduce the effective MTU by adding encapsulation headers.
- Ensure tunnel header overhead is accounted for in initial design documentation.
- Configure TCP MSS Clamping on edge/transit routers where required.
- Perform manual PMTUD testing on live nodes using `ping -f -l
` commands.