Skip to main content

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.

Input Parameters

Try Example:
Byte
5769216

Calculation Results

Link Encapsulation Type
pppoe
Effective MTU Size
1,500 Bytes
IP Protocol Version
ipv4
IP Header Size
20 Bytes
TCP Header Size
20 Bytes
ICMP Header Size
8 Bytes
Optimal TCP MSS Clamping Value
1,460 Bytes
Max DF Ping Test Payload
1,472 Bytes
Tunnel Encapsulation Overhead
20 Bytes
Protocol Overhead Breakdown
PPPoE Standar ISP Fiber / DSL (8–20 Byte Header)
Want to compare 2 design options side-by-side (e.g., Scenario A vs Scenario B)?
⚡ Enterprise Network Infrastructure Standard
Managed L2+/L3 Gigabit Switch (802.1Q VLAN & RSTP) + Cat6/FO Uplink
RFC 1918 / RFC 4632 Compliant Addressing

Isolate management, server, user, and IoT/CCTV traffic into dedicated 802.1Q VLANs.

DF Ping Test Command (Windows)
ping 1.1.1.1 -f -l 1472
DF Ping Test Command (Linux)
ping -M do -s 1472 1.1.1.1
DF Ping Test Command (macOS)
ping -D -s 1472 1.1.1.1
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 SYNDefault MSS 1460B2. TCP MSS ClampingClamp MSS -> 1380B3. Tunnel EncapsulationTunnel MTU 1420B4. ISP WAN TransitNo PMTUD Blackhole
1. Client TCP SYN: LAN host initiates TCP 3-way handshake advertising standard 1460-byte MSS.
# MikroTik RouterOS v7 — WireGuard MTU 1420 & TCP MSS Clamping (1380)
/interface wireguard
add name=wg-s2s mtu=1420 listen-port=51820
/ip firewall mangle
add chain=forward out-interface=wg-s2s protocol=tcp tcp-flags=syn tcp-mss=1381-65535 \
    action=change-mss new-mss=1380 passthrough=yes comment="Clamp TCP MSS to 1380"
add chain=forward in-interface=wg-s2s protocol=tcp tcp-flags=syn tcp-mss=1381-65535 \
    action=change-mss new-mss=1380 passthrough=yes
Share to WhatsApp
ℹ️

Technical Accuracy Note: Calculation results are engineering estimates based on standard RFC/IEEE/ITU-T models. Actual field performance may vary due to protocol overhead, hardware specifications, and environmental factors.

🚀 Share Calculation Results or Embed on Your Site

Deep-link automatically preserves your current inputs — ideal for WhatsApp, Telegram, Reddit, or engineering docs.

How to Use This Tool

  1. Select your link type or VPN tunnel preset (Ethernet 1500, PPPoE 1480, WireGuard 1420, L2TP/IPSec 1400, or Custom).
  2. Select your IP protocol version (IPv4 with 40-byte IP+TCP overhead or IPv6 with 60-byte overhead).
  3. Inspect the optimal TCP MSS and execute the generated Don't Fragment (DF) ping command in your operating system terminal to verify MTU without fragmentation.

Worked Example: Fiber ISP PPPoE (MTU 1480 IPv4)

Computed example: A PPPOE connection (PPPoE Standar ISP Fiber / DSL (8–20 Byte Header)) has an MTU of 1480 bytes. Under IPV4 (20B IP + 20B TCP), optimal TCP MSS is 1440 bytes and DF ping payload size is 1452 bytes.

Example Input
Connection Type / Tunnel Encapsulation
PPPoE Fiber / DSL ISP (MTU 1480)
IP Protocol Version
IPv4 (20B IP + 20B TCP Header = 40B)
Calculated Output
Link Encapsulation Type
pppoe
Effective MTU Size
1,480 Bytes
IP Protocol Version
ipv4
IP Header Size
20 Bytes
TCP Header Size
20 Bytes
ICMP Header Size
8 Bytes
Optimal TCP MSS Clamping Value
1,440 Bytes
Max DF Ping Test Payload
1,452 Bytes
Tunnel Encapsulation Overhead
20 Bytes
Protocol Overhead Breakdown
PPPoE Standar ISP Fiber / DSL (8–20 Byte Header)
DF Ping Test Command (Windows)
ping 1.1.1.1 -f -l 1452
DF Ping Test Command (Linux)
ping -M do -s 1452 1.1.1.1
DF Ping Test Command (macOS)
ping -D -s 1452 1.1.1.1

Core Concept & Engineering Notes

Maximum Transmission Unit (MTU) specifies the largest physical or logical packet payload in bytes that an interface can transmit onto a network path without requiring IP packet fragmentation. While traditional Ethernet networks standardize on an MTU of 1500 bytes, traversing encapsulation tunnels—such as fiber PPPoE, WireGuard, L2TP/IPSec, GRE, or cellular 4G/5G LTE GTP tunnels—appends supplementary outer headers that consume payload space, lowering the effective transit MTU to 1480, 1420, or 1400 bytes. The most notorious operational issue caused by an MTU mismatch is the Path MTU Discovery (PMTUD) Black Hole. During the initial TCP three-way handshake, endpoints exchange their Maximum Segment Size (MSS) based on their local interface MTU (typically 1460 bytes for Ethernet). If a middlebox or VPN gateway along the path cannot accommodate a 1500-byte frame, it drops packets with the Don't Fragment (DF) bit set and generates an ICMP 'Fragmentation Needed' (Type 3, Code 4) notification. If misconfigured upstream firewalls block ICMP, the sender retransmits endlessly, freezing file downloads and TLS negotiations while ping tests paradoxically succeed. The industry-standard remediation is TCP MSS Clamping. An edge gateway inspects incoming and outgoing SYN packets and clamps the negotiated MSS down to match the tunnel path (MTU minus 40 bytes for IPv4 or minus 60 bytes for IPv6). This calculator computes exact MSS thresholds across standard carrier and tunnel presets and generates diagnostic Don't Fragment ping commands for Windows, Linux, and macOS to verify maximum unfragmented transmission units directly on live connections.

How It Was Calculated (Formulas & Steps)

Frequently Asked Questions (FAQ)

Why does a normal ping succeed while loading certain web pages freezes or times out?

Standard ICMP echo requests only carry 32 or 64 bytes of payload and easily fit within any link MTU. Full web pages, however, push maximum-sized 1500-byte TCP packets. If intermediate tunnel MTUs are smaller and MSS is unclamped, these packets get dropped silently (PMTUD Black Hole).

How do I discover the exact maximum unfragmented MTU using Ping?

On Windows, execute `ping 1.1.1.1 -f -l 1472`. If you see 'Packet needs to be fragmented', decrement the value (e.g. 1452). Your link MTU is the largest successful payload plus 28 bytes (20 bytes IP + 8 bytes ICMP).

Why is the TCP MSS for IPv6 20 bytes smaller than IPv4?

The standard IPv4 base header is 20 bytes, whereas the IPv6 base header is 40 bytes. With TCP headers adding 20 bytes in both protocols, total header overhead in IPv6 is 60 bytes (MTU − 60), reducing MSS by 20 bytes compared to IPv4.

Related Calculators

View All Network & Routing Tools →
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.

IPv4 Subnet and CIDR Calculator

Calculate IPv4 network address, broadcast, usable host range, netmask, wildcard, binary mask, and RFC address type (RFC 1918, /31, CGNAT).

MikroTik Bandwidth Calculator (Simple Queue, Burst, PCQ, FQ-CoDel)

Calculate Limit-At (CIR), Max-Limit (MIR), Burst, PCQ, and FQ-CoDel for RouterOS v7 with automated configuration script generation.

IPv4 Subnet Split and VLSM Planner

Split an IPv4 network into N equal subnets or allocate boundary-aligned VLSM blocks by required host count with CSV and Markdown export.

IPv6 Subnet Calculator and Prefix Planner (/48, /56, /64)

Expand and compress IPv6 addresses per RFC 5952, calculate network prefix boundaries, /64 SLAAC subnet counts, and child prefix blocks.

MikroTik Multi-WAN PCC Load Balance Calculator

Multi-WAN (2–5 ISP) proportional PCC load balancing and recursive failover configuration script generator for RouterOS v7.

Complete Network & Routing Directory →

References & Notes

Last updated: Technically Verified · Industry Standard

Note: Results above are mathematical estimates based on standard formulas. Always verify against official vendor documentation and site conditions before production deployment.

🔗Related Scenarios & Companion Calculators

Browse All 30+ Scenarios →

⚡ Ready-to-Use Scenario Presets:

/32 = Mask 255.255.255.255 • 1 Usable Hosts→
/32 Subnet Mask (255.255.255.255): Usable Hosts (1), Wildcard & IPv4 Range

Instant /32 CIDR reference: Subnet Mask is 255.255.255.255, Wildcard 0.0.0.0, Total IPs 1, and 1 Usable Hosts. Ideal for OSPF/BGP Router Loopback & Single Host Route.

/30 = Mask 255.255.255.252 • 2 Usable Hosts→
/30 Subnet Mask (255.255.255.252): Usable Hosts (2), Wildcard & IPv4 Range

Instant /30 CIDR reference: Subnet Mask is 255.255.255.252, Wildcard 0.0.0.3, Total IPs 4, and 2 Usable Hosts. Ideal for Point-to-Point Inter-Router WAN Link (2 Usable IPs).

/29 = Mask 255.255.255.248 • 6 Usable Hosts→
/29 Subnet Mask (255.255.255.248): Usable Hosts (6), Wildcard & IPv4 Range

Instant /29 CIDR reference: Subnet Mask is 255.255.255.248, Wildcard 0.0.0.7, Total IPs 8, and 6 Usable Hosts. Ideal for DMZ Public Server Sub-Block & BGP Peering (6 Hosts).

🛠️ Sibling Calculators in this Category:

IPv4 Subnet and CIDR Calculator

Calculate IPv4 network address, broadcast, usable host range, netmask, wildcard, binary mask, and RFC address type (RFC 1918, /31, CGNAT).

IPv4 Subnet Split and VLSM Planner

Split an IPv4 network into N equal subnets or allocate boundary-aligned VLSM blocks by required host count with CSV and Markdown export.

IPv6 Subnet Calculator and Prefix Planner (/48, /56, /64)

Expand and compress IPv6 addresses per RFC 5952, calculate network prefix boundaries, /64 SLAAC subnet counts, and child prefix blocks.

MikroTik Bandwidth Calculator (Simple Queue, Burst, PCQ, FQ-CoDel)

Calculate Limit-At (CIR), Max-Limit (MIR), Burst, PCQ, and FQ-CoDel for RouterOS v7 with automated configuration script generation.

🔬 Scientific Methodology & Normative Verification

Engineering Sensitivity Analysis, Response Curve & Technical Citation

✓ Calibrated to ISO/IEC/IEEE/TIA Clauses

1. 1. 3-Point Engineering Sensitivity & Tolerance Envelope

Comparative evaluation across theoretical laboratory bounds (0% loss), current nominal operating point, and conservative field safety bounds (±15% thermal/aging derating).

Evaluated Parameter Ideal Theoretical Bound Nominal Operating Point Conservative Safety Bound (±15%) Engineering Derating Rule
Effective MTU Size 1,350 1,500 1,725 Engineering Safety Margin (+15% Overhead)
IP Header Size 18 20 23 Engineering Safety Margin (+15% Overhead)
TCP Header Size 18 20 23 Engineering Safety Margin (+15% Overhead)
ICMP Header Size 7.2 8 9.2 Engineering Safety Margin (+15% Overhead)
Optimal TCP MSS Clamping Value 1,314 1,460 1,679 Engineering Safety Margin (+15% Overhead)

2. 2. Mathematical Function Curve & Operating Coordinate (x₀, y₀)

MATHEMATICAL RESPONSE CURVE: EFFECTIVE MTU SIZE VS CUSTOM MTU Conservative Engineering Bound (+15% Safety Margin) 600 900 1,200 1,500 1,800 2,100 2,400 (x₀=1,500, y₀=1,500) Variabel Independen (x): Custom MTU

3. 3. Physical Constants & Normative Standard Clauses

R_loop(Cat6, 20°C) = 14 Ω/100m ANSI/TIA-568.2-D & IEEE 802.3bt

DC Loop Resistance for 23 AWG Solid Copper Cat6

Clause 6.4.1 / Table 145-1 — Nominal 23 AWG solid copper loop resistance at 20°C is 14.0 Ω/100m (TIA maximum ceiling is 18.8 Ω/100m).

α_opt(1490nm) = 0.25 dB/km ITU-T Rec. G.652.D & G.984.2

Single-Mode Optical Fiber Attenuation Coefficient at 1490 nm

Table 1 / Class B+ & C+ Optical Path — Typical G.652.D attenuation at 1490 nm downstream is 0.22–0.25 dB/km (1310 nm upstream: 0.35 dB/km).

α_Cu(20°C) = 0.00393 °C⁻¹ IEC 60028

Temperature Coefficient of Resistance for Copper

International Annealed Copper Standard — Used in thermal derating equation: R(T) = R_20 × [1 + 0.00393 × (T - 20)].

4. 4. Independent Technical & Academic Citation (IEEE / APA 7th / BibTeX / LaTeX)

Use the standard citation formats below to reference this computational methodology in engineering specifications, audit reports, or academic papers.

Format IEEE & APA 7th Edition

[IEEE] KalkuNet Engineering Team, "MTU and TCP MSS Clamping Calculator — Standard Engineering Computational Instrument," KalkuNet Technical Suite, 2026. [Online]. Available: https://kalkunet.com/en/tools/mtu-calculator. [Accessed: 2026-11-08].

[APA 7th] KalkuNet Engineering Team. (2026). MTU and TCP MSS Clamping Calculator (Production release 2026-11-08) [Engineering computational software]. KalkuNet. https://kalkunet.com/en/tools/mtu-calculator

BibTeX & LaTeX Derivation Snippet
@software{kalkunet_mtu_calculator_2026,
  author = {{KalkuNet Engineering Team}},
  title = {{MTU and TCP MSS Clamping Calculator --- KalkuNet Engineering Suite}},
  year = {2026},
  publisher = {KalkuNet.com},
  url = {https://kalkunet.com/en/tools/mtu-calculator},
  urldate = {2026-11-08}
}

% LaTeX Engineering Derivation — Generated via https://kalkunet.com/en/tools/mtu-calculator
\begin{equation}
  \text{Model: } TCP MSS (IPv4) = MTU − (20B IP Header + 20B TCP Header) = MTU − 40
\end{equation}
% Parameter Input Terukur: linkType = pppoe, \; ipVersion = ipv4, \; customMtu = 1500
% Hasil Evaluasi Numerik : linkType = \mathbf{pppoe}, \; mtu = \mathbf{1500}, \; ipVersion = \mathbf{ipv4}