MTU and MSS Calculator | VPN Tunnel Overhead

MTU and MSS calculator for WireGuard, IPsec, VXLAN, GRE and PPPoE: stack tunnel layers to get the inner MTU, TCP MSS and clamp commands. Free.

Also known as: mtu calculator · mss calculator · tcp mss calculator · wireguard mtu calculator · ipsec mtu calculator · vxlan mtu overhead · gre tunnel mtu · pppoe mtu 1492 · mss clamping calculator · tunnel overhead calculator

network tools

devops and infrastructure tools

networking

Encapsulation Stack

1 layer

Common setups

Underlay MTU

1500 for Ethernet, 9000 for jumbo frames.

Traffic inside the tunnel

Sets which MSS the commands use.

Layers, outermost first

MTU and MSS Result

The overhead of each layer, the inner MTU, the TCP MSS and ready-to-paste clamp commands will appear here.

About MTU and MSS Calculator

An MTU and MSS calculator is used to stop VPN and overlay traffic from fragmenting or silently stalling. Stack the encapsulations a packet passes through, such as PPPoE, WireGuard, IPsec, VXLAN or GRE, and it returns the largest inner MTU that still fits the physical link, the TCP MSS to clamp, the overhead of every layer, and the commands to set and test them.

Key Features

Stacks up to 8 layers outermost first, with IPv4 or IPv6 outer headers per layer
Models IPsec ESP padding exactly for AES-GCM and AES-CBC with SHA1, SHA2-256, SHA2-384 and SHA2-512, with or without NAT-T
Handles GRE over IPsec transport mode, where the GRE header sits inside the encrypted payload
Reports the MSS for both IPv4 and IPv6 traffic inside the tunnel
Generates ip link, wg-quick, iptables, nftables and Cisco IOS lines plus Don't Fragment ping tests
Presets for WireGuard over PPPoE, Kubernetes VXLAN, AWS Site-to-Site VPN and Cisco GRE over IPsec

Use Cases

Fix SSH sessions that connect over WireGuard but hang the moment a large file or git push starts
Pick the MTU for a WireGuard tunnel on a CenturyLink fiber line, which authenticates over PPPoE
Set MSS clamping on a customer gateway for an AWS Site-to-Site VPN using AES-GCM
Size the pod network MTU for a Kubernetes cluster running Flannel or Calico in VXLAN mode
Work out how much of a 9000-byte jumbo frame survives a VXLAN overlay in a data center
Explain to a reviewer why a GRE over IPsec tunnel needs a smaller MSS than plain IPsec

Supported Formats

PPPoE, MPLS, GRE, IP-in-IP, 6in4, VXLAN, GENEVE, WireGuard, IPsec ESP

IPv4 and IPv6 outer and inner headers

Underlay MTU from 576 to 65,535 bytes

Related Keywords

mtu calculator

mss calculator

tcp mss calculator

wireguard mtu calculator

ipsec mtu calculator

vxlan mtu overhead

gre tunnel mtu

pppoe mtu 1492

mss clamping calculator

tunnel overhead calculator

Why is WireGuard's default MTU 1420 and not 1440?

WireGuard adds a 20-byte outer IPv4 header, an 8-byte UDP header and 32 bytes of its own (a 16-byte data header and a 16-byte Poly1305 tag), which is 60 bytes and would allow 1440 on a 1500-byte link. If the outer path is IPv6, the outer header is 40 bytes and the total is 80, so 1500 - 80 = 1420. wg-quick picks 1420 because it fits either way. On a PPPoE line the link itself is only 1492 bytes, so even 1420 is fine over IPv4, but a stack of PPPoE and WireGuard over IPv6 needs 1412. When a tunnel MTU is too large, small packets work and large ones vanish, which is why SSH logins succeed while file transfers hang.

Calculated in your browser

All arithmetic runs locally in JavaScript. Nothing about your network design or addressing is sent anywhere.

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Frequently asked questions

What is MTU and MSS Calculator used for?

MTU and MSS calculator for WireGuard, IPsec, VXLAN, GRE and PPPoE: stack tunnel layers to get the inner MTU, TCP MSS and clamp commands. Free.

Is MTU and MSS Calculator free to use?

Yes. MTU and MSS Calculator is completely free with no usage limits, and there is no paid tier required to use it.

Do I need an account to use MTU and MSS Calculator?

No. MTU and MSS Calculator works immediately in your browser with no signup, login, or email address required.

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