{"uid":"cap_uxKFqzIReMhNEsz4FXQiQ","slug":"network-calc-mtu-mss-calculator-7e3e14a9","name":"Network Calc MTU/MSS Calculator","description":"TCP MSS from an MTU for IPv4 or IPv6, effective MTU through tunnels (PPPoE, GRE, VXLAN, WireGuard) and IPv4 fragment counts.","url":"https://network-calc.x402tookit.com/mtu-mss?utm_source=zero.xyz","method":"GET","headers":{},"bodySchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","required":["input"],"properties":{"input":{"type":"object","required":["type","method"],"properties":{"type":{"type":"string","const":"http"},"method":{"enum":["GET"],"type":"string"},"queryParams":{"type":"object","required":["mtu"],"properties":{"mtu":{"type":"integer","description":"Link MTU in bytes (the IP packet size, 1500 for Ethernet)"},"tunnel":{"enum":["none","pppoe","gre","gre-ipv6","ipip","vxlan","geneve","wireguard-ipv4","wireguard-ipv6","mpls"],"type":"string","description":"Encapsulation: none, pppoe, gre, gre-ipv6, ipip, 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TCP MSS from a given MTU for IPv4/IPv6, computes effective MTU through tunnels (PPPoE, GRE, VXLAN, WireGuard, etc.), and counts IPv4 fragments for a payload size.","exampleAgentPrompt":"What is the TCP MSS and effective MTU for a WireGuard-over-IPv4 tunnel on a standard 1500-byte Ethernet link, using IPv4 with TCP timestamps enabled?","exampleUseCases":[{"title":"PPPoE MSS clamping for DSL router","prompt":"I have a DSL connection using PPPoE with a 1500-byte physical MTU — what TCP MSS value should I clamp to for IPv4 so connections don't stall?"},{"title":"VXLAN overlay effective MTU check","prompt":"My VXLAN overlay network sits on top of a 9000-byte jumbo Ethernet link — what is the effective MTU and TCP MSS for IPv4 traffic inside the tunnel?"},{"title":"IPv4 fragmentation count for large UDP payload","prompt":"If I send a 4096-byte UDP datagram (including the 8-byte header) over an IPv4 link with a 1500-byte MTU and no tunnel, how many fragments will it produce and how big are they?"}],"resultDescription":"Returns the computed TCP MSS in bytes, the effective MTU after tunnel overhead deductions, the recommended MSS clamp value, fragmentation details (fragment count, per-fragment payload bytes, total IP bytes) when a payload size is provided, a human-readable summary, tunnel-specific notes, and any warnings or reasons behind the computed values.","failureModes":["Missing required 'mtu' parameter returns a validation error","Invalid tunnel enum value returns a 400 bad request","MTU value below minimum (e.g. below 68 for IPv4) may return an error or edge-case result","Requesting IPv6 fragmentation counts may return a not-applicable note since IPv6 does not fragment in transit","Malformed query parameters return schema validation errors"],"whenToPreferThis":"Use this endpoint when you need precise TCP MSS values for a specific MTU and tunnel combination, particularly when configuring firewall MSS clamping rules, diagnosing TCP black-hole issues through tunnels, or calculating IPv4 fragment counts for large UDP payloads. It covers a wide range of tunnel types (PPPoE, GRE, VXLAN, WireGuard, MPLS, etc.) and handles both IPv4 and IPv6, making it more specialized and accurate than manual header-subtraction calculations.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-10-29T13:13:43.169Z","isFirstParty":false,"canonicalSlug":"network-calc-mtu-mss-calculator-7e3e14a9"}