VPN Encryption Overhead & Tunnel MTU Calculator (WireGuard, IPsec, OpenVPN)
Calculate cryptographic encapsulation overhead, optimal tunnel MTU, TCP MSS clamping, and effective payload throughput for WireGuard, IPsec, and OpenVPN.
Input Parameters
Try Example:
Calculation Results
VPN Tunnel Payload Efficiency (%)93.33%
- Physical WAN Interface MTU
- 1,500 Bytes
- Outer Carrier IP Header Size
- 20 Bytes
- VPN Encapsulation & Cipher Overhead
- 40 Bytes
- Total Tunnel Header Overhead per Packet
- 60 Bytes
- Optimal VPN Tunnel Interface MTU
- 1,440 Bytes
- Optimal TCP MSS Clamping Value
- 1,400 Bytes
- Inner TCP Segment Payload Size
- 1,400 Bytes
- Protocol Payload Transmission Efficiency
- 93.33 %
- Effective Usable Payload Throughput
- 93.33 Mbps
- Bandwidth Consumed by Encapsulation
- 6.67 Mbps
Want to compare 2 design options side-by-side (e.g., Scenario A vs Scenario B)?
⚡ Production Security & Ops Standard
Debian 12 / Ubuntu 24.04 LTS + Nftables + Systemd Timer
CIS Benchmark Level 1 • Non-Root SSH Key-Only + Fail2ban/CrowdSec
Validate firewall rulesets and cron timers in staging before production rollout.
Overhead, MTU & Throughput Comparison Across VPN Protocols
| VPN Protocol & Cipher | Tunnel Encapsulation Overhead | Optimal VPN Tunnel Interface MTU | Optimal TCP MSS Clamping Value | Effective Usable Payload Throughput |
|---|---|---|---|---|
| WireGuard (UDP 8B + WG Header 32B + Poly1305 16B) | 60 Bytes | 1,440 Bytes | 1,400 Bytes | 93.33 Mbps |
| IPsec ESP AES-GCM Native (Proto 50) | 66 Bytes | 1,434 Bytes | 1,394 Bytes | 92.93 Mbps |
| IPsec ESP AES-GCM + UDP NAT-T (4500) | 74 Bytes | 1,426 Bytes | 1,386 Bytes | 92.4 Mbps |
| OpenVPN 2.6 Data Channel AEAD (UDP) | 68 Bytes | 1,432 Bytes | 1,392 Bytes | 92.8 Mbps |
| OpenVPN Data Channel (TCP) | 80 Bytes | 1,420 Bytes | 1,380 Bytes | 92 Mbps |
| GRE Tunnel (24B) + IPsec ESP NAT-T | 98 Bytes | 1,402 Bytes | 1,362 Bytes | 90.8 Mbps |
MTU & TCP MSS Clamping Rules (RouterOS & Linux)
# Konfigurasi Interface MTU & TCP MSS Clamping (MikroTik RouterOS v7 & Linux) /interface wireguard set [find] mtu=1440 /ip firewall mangle add chain=forward protocol=tcp tcp-flags=syn action=change-mss new-mss=1400 passthrough=yes comment="VPN MSS Clamping" # Linux iptables equivalent: iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1400
Multi-Vendor CLI & Packet Flow
Multi-Vendor Config Translator & Interactive Packet Flow Visualizer
Interactive Packet Flow Pipeline (Click Stage to Inspect)WAN ➔ Prerouting/NAT ➔ Filter/QoS ➔ LAN
1. Client TCP SYN: LAN host initiates TCP 3-way handshake advertising standard 1460-byte MSS.
# MikroTik RouterOS v7 — WireGuard MTU 1440 & TCP MSS Clamping (1400)
/interface wireguard
add name=wg-s2s mtu=1440 listen-port=51820
/ip firewall mangle
add chain=forward out-interface=wg-s2s protocol=tcp tcp-flags=syn tcp-mss=1401-65535 \
action=change-mss new-mss=1400 passthrough=yes comment="Clamp TCP MSS to 1400"
add chain=forward in-interface=wg-s2s protocol=tcp tcp-flags=syn tcp-mss=1401-65535 \
action=change-mss new-mss=1400 passthrough=yesHow to Use This Tool
- Enter the physical WAN interface MTU (1500 for standard Ethernet or 1492 for PPPoE fiber links) and select the outer IP version (IPv4 or IPv6).
- Choose the active VPN tunnel protocol (WireGuard, IPsec ESP NAT-T, IPsec Native, OpenVPN UDP/TCP, or GRE + IPsec) and enter the link speed in Mbps.
- Review the optimal Tunnel MTU, TCP MSS clamping value, protocol payload efficiency, and copy the generated MikroTik RouterOS or Linux iptables mangle rules.
Worked Example: WireGuard over Standard Ethernet (MTU 1500, 100 Mbps)
Worked example: A 1500-byte Ethernet WAN link running WireGuard over IPv4 incurs 60 bytes of total tunnel overhead, yielding an optimal Tunnel MTU of 1440 bytes, TCP MSS of 1400 bytes, and 93.33% payload efficiency.
Example Input
- Physical WAN Interface MTU (Bytes)
- 1,500 Bytes
- Outer Carrier IP Protocol Version
- IPv4 Carrier (20-Byte Outer IP Header)
- VPN Tunnel Protocol & Cipher Suite
- WireGuard (ChaCha20-Poly1305 over UDP)
- WAN Link Bandwidth Speed (Mbps)
- 100 Mbps
Calculated Output
- Physical WAN Interface MTU
- 1,500 Bytes
- Outer Carrier IP Header Size
- 20 Bytes
- VPN Encapsulation & Cipher Overhead
- 40 Bytes
- Total Tunnel Header Overhead per Packet
- 60 Bytes
- Optimal VPN Tunnel Interface MTU
- 1,440 Bytes
- Optimal TCP MSS Clamping Value
- 1,400 Bytes
- Inner TCP Segment Payload Size
- 1,400 Bytes
- Protocol Payload Transmission Efficiency
- 93.33 %
- Effective Usable Payload Throughput
- 93.33 Mbps
- Bandwidth Consumed by Encapsulation
- 6.67 Mbps
- MTU & TCP MSS Clamping Rules (RouterOS & Linux)
- # Konfigurasi Interface MTU & TCP MSS Clamping (MikroTik RouterOS v7 & Linux) /interface wireguard set [find] mtu=1440 /ip firewall mangle add chain=forward protocol=tcp tcp-flags=syn action=change-mss new-mss=1400 passthrough=yes comment="VPN MSS Clamping" # Linux iptables equivalent: iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --set-mss 1400
Overhead, MTU & Throughput Comparison Across VPN Protocols
| VPN Protocol & Cipher | Tunnel Encapsulation Overhead | Optimal VPN Tunnel Interface MTU | Optimal TCP MSS Clamping Value | Effective Usable Payload Throughput |
|---|---|---|---|---|
| WireGuard (UDP 8B + WG Header 32B + Poly1305 16B) | 60 Bytes | 1,440 Bytes | 1,400 Bytes | 93.33 Mbps |
| IPsec ESP AES-GCM Native (Proto 50) | 66 Bytes | 1,434 Bytes | 1,394 Bytes | 92.93 Mbps |
| IPsec ESP AES-GCM + UDP NAT-T (4500) | 74 Bytes | 1,426 Bytes | 1,386 Bytes | 92.4 Mbps |
| OpenVPN 2.6 Data Channel AEAD (UDP) | 68 Bytes | 1,432 Bytes | 1,392 Bytes | 92.8 Mbps |
| OpenVPN Data Channel (TCP) | 80 Bytes | 1,420 Bytes | 1,380 Bytes | 92 Mbps |
| GRE Tunnel (24B) + IPsec ESP NAT-T | 98 Bytes | 1,402 Bytes | 1,362 Bytes | 90.8 Mbps |
Core Concept & Engineering Notes
Every Virtual Private Network (VPN) protocol encapsulates original inner IP packets inside outer transport, tunnel, and cryptographic authentication headers before transmitting them across a public WAN link. This encapsulation overhead reduces the maximum payload space available within a single physical network frame, lowering the effective Maximum Transmission Unit (MTU) of the virtual tunnel interface. If the tunnel MTU is not accurately aligned with the underlying WAN path MTU (such as 1500-byte standard Ethernet or 1492-byte PPPoE fiber), oversized packets suffer mid-flight IP fragmentation or silent drops when the Don't Fragment (DF) flag is set.
Total encapsulation overhead varies by VPN protocol and outer IP family (20-byte IPv4 vs 40-byte IPv6). WireGuard employs fixed-size ChaCha20-Poly1305 AEAD framing over UDP, adding 20 bytes of outer IPv4 (or 40 bytes of IPv6) + 8 bytes UDP + 32 bytes WireGuard header/AEAD tag, resulting in 60 bytes of overhead on IPv4 (1440 MTU) or 80 bytes on IPv6 (1420 default MTU). Conversely, IPsec ESP operating over UDP NAT-Traversal (port 4500), OpenVPN, and GRE-over-IPsec introduce additional session headers, initialization vectors (IV), and cipher padding that consume 66 to 98 bytes per packet.
To eliminate Path MTU Discovery (PMTUD) blackholes—where ICMP Fragmentation Needed packets are blocked by intermediate firewalls, causing HTTPS TLS handshakes and SSH sessions to stall—network engineers configure TCP MSS (Maximum Segment Size) clamping on border routers (MikroTik Mangle or Linux iptables). The optimal TCP MSS equals the Tunnel MTU minus 40 bytes (20-byte inner IPv4 header + 20-byte inner TCP header).
Beyond preventing packet drops, protocol overhead directly governs effective usable throughput (goodput) and router CPU utilization. Every byte consumed by outer IP, UDP, ESP, or AEAD authentication headers reduces the ratio of application payload per physical frame. On 1492-byte PPPoE broadband links running multi-layered tunnels such as GRE over IPsec or OpenVPN over TCP, header overhead can consume nearly 8% to 10% of raw link capacity while risking TCP-over-TCP retransmission amplification. Calculating exact tunnel MTU and MSS boundaries ahead of deployment ensures maximum wire-speed efficiency across site-to-site and road-warrior VPN topologies.
How It Was Calculated (Formulas & Steps)
Mathematical Formulas
- Total Tunnel Overhead = Outer_IP_Header (20B/40B) + VPN_Encapsulation_&_AEAD_Tag_Bytes
- Optimal Tunnel MTU = Physical_WAN_MTU − Total_Tunnel_Overhead
- Optimal TCP MSS Clamping = Optimal_Tunnel_MTU − 40 bytes (20B Inner IPv4 + 20B Inner TCP)
- Payload Efficiency (%) = (Optimal_TCP_MSS ÷ Physical_WAN_MTU) × 100%
Step-by-Step Calculation
- MTU WAN Fisik = 1500 byte, Header IP Luar (IPV4) = 20 byte.
- Enkapsulasi & Cipher WireGuard (UDP 8B + WG Header 32B + Poly1305 16B) = 40 byte.
- Total Overhead Tunnel = 20 + 40 = 60 byte.
- MTU Interface VPN Optimal = 1500 - 60 = 1440 byte.
- TCP MSS Clamping Optimal = 1440 - 40 (Header IPv4 20B + TCP 20B dalam tunnel) = 1400 byte.
- Efisiensi Payload TCP = (1400 / 1500) × 100% = 93.33% (93.33 Mbps dari link 100 Mbps).
Frequently Asked Questions (FAQ)
Why does WireGuard default to an interface MTU of 1420 bytes?
WireGuard chooses 1420 bytes so a single tunnel configuration safely traverses both IPv4 (20-byte header) and IPv6 (40-byte header) carriers over a 1500-byte Ethernet link (1500 - 80 bytes = 1420 bytes).
What WireGuard MTU should be used when the ISP WAN link uses PPPoE (MTU 1492)?
Because PPPoE consumes 8 bytes and lowers the WAN MTU to 1492 bytes, the WireGuard MTU should be reduced to 1432 bytes (IPv4-only carrier) or 1412 bytes (IPv6-compatible), with a TCP MSS of 1392 or 1372 bytes.
What symptoms occur when the VPN MTU is too high and MSS clamping is missing?
Small ICMP pings succeed normally, but loading HTTPS websites, transferring files, or returning large SSH/SQL payloads hangs indefinitely because full-sized TCP segments with the DF bit set are dropped along the path.
Why is OpenVPN in TCP mode discouraged for site-to-site tunnels?
Beyond higher header overhead (60+ bytes), encapsulating inner TCP streams inside an outer TCP tunnel triggers TCP-over-TCP meltdown—where packet loss causes competing congestion backoff and duplicate retransmissions.
Related Calculators
View All Developer & Security Tools →MTU and TCP MSS Clamping Calculator
Calculate optimal MTU sizes, TCP MSS clamping (IPv4/IPv6), and Don't Fragment ping payloads to resolve web page freezes over PPPoE and VPN tunnels.
MikroTik WireGuard VPN MTU & MSS Calculator
Deploy site-to-site WireGuard VPN on RouterOS v7 with automatic TCP MSS Clamping to prevent tunnel web page freezes and PMTUD black holes.
JWT Token Size, Base64URL Overhead & TTL Calculator
Calculate JWT token byte size (HS256, RS256, ES256, EdDSA), Base64URL overhead, 4 KB browser cookie and 8 KB Nginx header limits, and monthly bandwidth.
Password Entropy & Brute-Force Crack Time Calculator
Calculate cryptographic password entropy bits (E = L × log2(R)), total keyspace combinations, and brute-force crack times across Bcrypt and GPU rigs.
SIEM Security Log Storage, EPS & Audit Retention Calculator
Calculate aggregate Events Per Second (EPS), daily raw log volume, indexed Hot Storage, and compressed Cold Archive capacity for Wazuh & Elastic SIEM.
References & Notes
Last updated: Technically Verified · Industry Standard
- WireGuard Protocol Cryptographic & Packet Header Specification (Jason A. Donenfeld)
- IETF RFC 4303 — IP Encapsulating Security Payload (ESP) & RFC 3948 UDP Encapsulation
Note: Results above are mathematical estimates based on standard formulas. Always verify against official vendor documentation and site conditions before production deployment.