Network Tools

MTU Test — Maximum Transmission Unit Calculator

Compute TCP/UDP payload limits from MTU and optionally probe host HTTPS reachability

Common MTU presets:

How to Use This Tool

  1. Enter MTU bytes (576–9000) or click Ethernet, PPPoE, WireGuard, or VPN presets.
  2. Optionally enter a hostname for HTTPS reachability probe.
  3. Server computes tcpPayloadIpv4, tcpPayloadIpv6, and udpPayloadIpv4 from your MTU.
  4. Reachability attempt reports HTTP status and latency when host is provided.
  5. Review embedded note about path MTU discovery limits in browser environments.

About This Tool

Wrong MTU causes silent performance collapse — VPN tunnels black-hole large packets, PPPoE links need 1492-byte frames, and jumbo LAN settings break when traffic crosses the internet. Rankify MTU test accepts an MTU byte value (default 1500), calculates maximum TCP and UDP IPv4/IPv6 payloads, lists common profile presets, and optionally probes a hostname with HTTPS to confirm reachability.

Browser-based tools cannot run ICMP fragmentation discovery, but arithmetic MTU planning prevents many support tickets before you change router or WireGuard settings.

Common use cases

  • •Pick MTU for VPN or PPPoE without fragmentation
  • •Calculate max TCP payload from interface MTU

Why use Rankify for ?

  • Instant payload math for firewall and VPN design.
  • Preset buttons for common link types.
  • Optional HTTPS reachability sanity check.
  • Clear IPv4 versus IPv6 TCP header size differences.
  • Free API at /ip-tools/api/mtu-test.

What MTU means

Maximum Transmission Unit is the largest layer-3 packet payload a link accepts without fragmentation. Ethernet commonly uses 1500 bytes. Subtract IP and TCP/UDP headers to get application payload limits our calculator displays.

Common MTU presets explained

1500 — standard Ethernet. 1492 — PPPoE DSL overhead. 1420 — typical WireGuard on 1500 underlying link. 1400 — conservative VPN tunnel when providers add encapsulation bytes.

TCP versus UDP payload rows

TCP headers are 20 bytes minimum on IPv4 (40 on IPv6). UDP is 8 bytes plus IP header. Our tool shows both IPv4 and IPv6 TCP payload caps so dual-stack apps size correctly.

Path MTU discovery reality

Real paths may enforce lower MTU than your LAN. Symptoms include HTTPS works for small pages but large downloads stall on VPN. Lower interface MTU or enable TCP MSS clamping on routers when suspected.

VPN and WireGuard tuning

Operators set InterfaceMTU and Peer MTU based on underlay minus encapsulation. Use this calculator before editing wg0.conf or OpenVPN tun-mtu directives.

Optional host reachability

Hostname probe confirms DNS resolves and TCP/443 responds — not that full MTU path works end-to-end. Combine with ping-test for latency baselines.

Pairing with network calculators

ip-network-calculator plans IPv4 subnets. Bandwidth calculator sizes throughput. MTU test completes the L2/L3 design trio for field engineers.

API usage

GET /ip-tools/api/mtu-test?mtu=1492&host=example.com returns computed payloads and optional reachability block.

Important notes & limitations

  • No ICMP packetization or DF-bit path MTU discovery from the browser stack.
  • Reachability uses HTTPS HEAD/GET — not raw MTU-sized probes.
  • Jumbo frames on LAN may not survive internet egress.

Frequently Asked Questions

Yes. Rankify offers this MTU test at no cost with no account required. Results load in real time.

We do not permanently store your queries on our servers. Some tools run entirely in your browser; others fetch public data for the request only.

Yes. Open the page in any modern phone or tablet browser. Results work on Wi‑Fi and mobile data.

No. It calculates theoretical payloads and optional HTTPS reachability only.

Tunnel headers consume bytes. WireGuard, IPsec, and PPPoE all reduce effective MTU.

1492 is the usual WAN MTU on many DSL/fiber PPPoE installs.

IPv6 header is 40 bytes versus 20 on IPv4, reducing TCP payload for the same MTU.

Use udpPayloadIpv4 as a sizing hint; application headers still consume bytes.

Reachability is independent of MTU arithmetic — check DNS, firewall, or TLS issues.

Next step for your check

Continue with ping test on Rankify.

Ping Test

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