Network MTU & MSS Overhead Calculator
Calculate fixed-header MSS or model PPPoE, basic GRE and WireGuard with per-layer byte budgets.
About this network mtu & mss overhead calculator
Calculate fixed-header MSS or model PPPoE, basic GRE and WireGuard with per-layer byte budgets Performs protocol inspection, IP calculation, and network analysis client-side without sending probes or exposing network topology.
Protocol mechanics & network logic
Choose a base Ethernet payload MTU, optional PPPoE, one tunnel and inner/outer IP versions. The independent live calculator shows each header and a conservative TCP MSS. The text calculator below retains fixed deductions of 40 bytes for IPv4 and 60 for IPv6.
Worked network diagnostic scenario
Scenario: Calculate the two fixed MSS values for a 1280-byte MTU.
Sample input:
Processing: Convert the text to a number, subtract 40 for IPv4 MSS and 60 for IPv6 MSS, then clamp at zero. PPPoE + basic GRE over IPv4: 1500 − 8 − 20 − 4 = 1468 inner MTU; IPv4 TCP MSS = 1428.
Illustrative output:
Addressing limits & protocol boundaries
Operational constraints and validation boundaries: Base MTU excludes Ethernet headers. PPPoE adds 8 bytes; basic GRE adds outer IP + 4; WireGuard adds outer IP + UDP 8 + 32. WireGuard capacity rounds down to 16-byte blocks to reserve padding. Only fixed IPv4 20, IPv6 40 and TCP 20-byte headers are modeled. No IP/TCP options, GRE extensions, IPsec, VXLAN, nested tunnels or path probing. Values are planning estimates, not router configuration or measured path MTU. The live panel accepts whole-byte MTUs from 1 to 65535 only when at least one TCP payload byte fits.
Addressing calculations and subnet models in Network MTU & MSS Overhead Calculator follow IETF RFC definitions. Ensure subnet masks and CIDR prefixes match your network topology.
Offline network inspection boundary
Address parsing and CIDR calculations in Network MTU & MSS Overhead Calculator run entirely client-side without probing external IP networks or transmitting routing data.
IETF RFC specifications & IANA registries
IETF Request for Comments (RFC) standards and IANA registry references:
Network MTU & MSS Overhead Calculator verification · Audit standards
How to use it
- Enter a nonnegative MTU.
- Subtract fixed 40-byte IPv4/TCP and 60-byte IPv6/TCP headers, flooring results at zero.
- Click the action button or observe immediate live calculations rendered by Network MTU & MSS Overhead Calculator.
Frequently asked questions
What fixed arithmetic does this MTU and MSS calculator use?+
It converts the single text input to a number and returns mtu, ipv4Mss as max(0, MTU minus 40), and ipv6Mss as max(0, MTU minus 60). The constants represent fixed IPv4-plus-TCP and IPv6-plus-TCP deductions.
Which input and output are actually available?+
Input 1280: mtu 1280; ipv4Mss 1240; ipv6Mss 1220.
What limits apply to the calculation?+
Base MTU excludes Ethernet headers.
What result should the documented example produce?+
Security isolation for "What result should the documented example produce?" ensures zero transmission beyond your local workstation.