VPN Encryption Overhead Calculator

ANA›Life Services Authority›National Calculator Authority›VPN Encryption Overhead Calculator

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VPN Encryption Overhead Calculator

Estimate the extra bandwidth consumption and packet size increase caused by VPN tunneling and encryption protocols (IPsec, OpenVPN, WireGuard).

Original Packet Payload Size (bytes)

Available Bandwidth (Mbps)

VPN Protocol

IPsec (AES-256-CBC + SHA-256 HMAC) IPsec (AES-128-CBC + SHA-1 HMAC) OpenVPN (UDP, AES-256-GCM) OpenVPN (TCP, AES-256-GCM) WireGuard (ChaCha20-Poly1305)

Packets Per Second (PPS)

Calculate

function vpnCalc() { var payload = parseFloat(document.getElementById('vpn-payload-size').value); var bandwidth = parseFloat(document.getElementById('vpn-bandwidth').value); var protocol = document.getElementById('vpn-protocol').value; var pps = parseFloat(document.getElementById('vpn-pps').value); var resultDiv = document.getElementById('vpn-result');

// --- Input Validation --- if (isNaN(payload) || payload 65535) { resultDiv.style.display = 'block'; resultDiv.innerHTML = '⚠ Payload size must be between 1 and 65535 bytes.'; return; } if (isNaN(bandwidth) || bandwidth ⚠ Bandwidth must be a positive number.'; return; } if (isNaN(pps) || pps ⚠ Packets per second must be at least 1.'; return; }

/ * ─── OVERHEAD COMPONENTS BY PROTOCOL ─────────────────────────────────────── * * IPsec Tunnel Mode (AES-256-CBC + SHA-256 HMAC): * Outer IP header : 20 bytes * ESP header : 8 bytes (SPI 4B + Seq 4B) * IV (AES-CBC) : 16 bytes * Padding : 0–15 bytes (avg 8, to reach AES 16-byte block boundary) * Pad Length + Next Hdr : 2 bytes * ESP Trailer : 2 bytes * HMAC-SHA-256 ICV : 16 bytes (truncated to 128 bits per RFC 4868) * Inner IP header : 20 bytes * Total fixed overhead : 20+8+16+2+16+20 = 82 bytes + avg 8 padding = ~90 bytes * * IPsec Tunnel Mode (AES-128-CBC + SHA-1 HMAC): * Same structure, IV=16B, ICV=12B (HMAC-SHA-1-96), avg padding=8B * Total fixed overhead : 20+8+16+2+12+20 = 78 bytes + avg 8 = ~86 bytes * * OpenVPN UDP (AES-256-GCM): * Outer IP header : 20 bytes * UDP header : 8 bytes * OpenVPN header : 1 byte (opcode + key_id) * Packet ID : 4 bytes * AEAD IV/nonce : 12 bytes (GCM 96-bit nonce) * GCM Auth Tag : 16 bytes * Total overhead : 20+8+1+4+12+16 = 61 bytes * * OpenVPN TCP (AES-256-GCM): * Outer IP header : 20 bytes * TCP header : 20 bytes * OpenVPN length field : 2 bytes * OpenVPN header : 1 byte * Packet ID : 4 bytes * AEAD IV/nonce : 12 bytes * GCM Auth Tag : 16 bytes * Total overhead : 20+20+2+1+4+12+16 = 75 bytes * * WireGuard (ChaCha20-Poly1305): * Outer IP header : 20 bytes * UDP header : 8 bytes * WireGuard header : 4 bytes (message type + reserved) * Receiver index : 4 bytes * Counter (nonce) : 8 bytes * Poly1305 Auth Tag : 16 bytes * Total overhead : 20+8+4+4+8+16 = 60 bytes * * References: * RFC 4303 (ESP), RFC 4868 (HMAC-SHA-2), RFC 2104 (HMAC), * OpenVPN 2.x protocol spec, WireGuard whitepaper (J. Donenfeld, 2017) /

var overheadBytes, protocolName, cipherInfo;

if (protocol === 'ipsec_aes256_sha256') { var blockSize = 16; // AES block size bytes var paddingAvg = (blockSize - (payload % blockSize)) % blockSize; if (paddingAvg === 0) paddingAvg = blockSize; // always at least 1 pad byte overheadBytes = 20 + 8 + 16 + 2 + 16 + 20 + paddingAvg; // outer IP + ESP hdr + IV + trailer + ICV + inner IP + padding protocolName = 'IPsec Tunnel (AES-256-CBC + HMAC-SHA-256)'; cipherInfo = 'Block cipher: AES-256-CBC (16-byte IV, 16-byte block). ICV: HMAC-SHA-256-128 (16 bytes).'; } else if (protocol === 'ipsec_aes128_sha1') { var blockSize = 16; var paddingAvg = (blockSize - (payload % blockSize)) % blockSize; if (paddingAvg === 0) paddingAvg = blockSize; overheadBytes = 20 + 8 + 16 + 2 + 12 + 20 + paddingAvg; protocolName = 'IPsec Tunnel (AES-128-CBC + HMAC-SHA-1-96)'; cipherInfo = 'Block cipher: AES-128-CBC (16-byte IV, 16-byte block). ICV: HMAC-SHA-1-96 (12 bytes).'; } else if (protocol === 'openvpn_udp') { overheadBytes = 20 + 8 + 1 + 4 + 12 + 16; protocolName = 'OpenVPN UDP (AES-256-GCM)'; cipherInfo = 'AEAD cipher: AES-256-GCM (12-byte nonce, 16-byte auth tag). No padding required.'; } else if (protocol === 'openvpn_tcp') { overheadBytes = 20 + 20 + 2 + 1 + 4 + 12 + 16; protocolName = 'OpenVPN TCP (AES-256-GCM)'; cipherInfo = 'AEAD cipher: AES-256-GCM (12-byte nonce, 16-byte auth tag). TCP framing adds 2-byte length field.'; } else { // wireguard overheadBytes = 20 + 8 + 4 + 4 + 8 + 16; protocolName = 'WireGuard (ChaCha20-Poly1305)'; cipherInfo = 'AEAD cipher: ChaCha20-Poly1305 (8-byte counter nonce, 16-byte Poly1305 tag). No padding required.'; }

// ─── CORE CALCULATIONS ────────────────────────────────────────────────────── // Encapsulated packet size var encapSize = payload + overheadBytes;

// Overhead percentage relative to original payload // overhead_pct = (overhead_bytes / payload) * 100 var overheadPct = (overheadBytes / payload) * 100;

// Effective throughput after overhead // effective_throughput = bandwidth * (payload / encap_size) var effectiveThroughput = bandwidth * (payload / encapSize);

// Throughput loss var throughputLoss = bandwidth - effectiveThroughput; var throughputLossPct = (throughputLoss / bandwidth) * 100;

// Extra bandwidth consumed by overhead at given PPS // overhead_bandwidth_Mbps = (overhead_bytes * 8 * pps) / 1,000,000 var overheadBandwidthMbps = (overheadBytes * 8 * pps) / 1e6;

// Total encapsulated bandwidth at given PPS // total_bw = (encap_size * 8 * pps) / 1,000,000 var totalBwMbps = (encapSize * 8 * pps) / 1e6;

// MTU fragmentation check (standard Ethernet MTU = 1500 bytes) var mtu = 1500; var fragmented = encapSize > mtu; var maxPayloadNoFrag = mtu - overheadBytes;

// ─── RENDER RESULTS ───────────────────────────────────────────────────────── resultDiv.style.display = 'block'; resultDiv.innerHTML = '### Results for ' + protocolName + ' ' + '' + 'Original Payload Size' + '' + payload.toFixed(0) + ' bytes' + 'VPN Overhead Added' + '' + overheadBytes.toFixed(0) + ' bytes (' + overheadPct.toFixed(2) + '% of payload)' + 'Encapsulated Packet Size' + '' + encapSize.toFixed(0) + ' bytes' + (fragmented ? ' (⚠ Exceeds MTU 1500 — fragmentation required)' : ' (✓ Within MTU 1500)') + '' + 'Max Payload Without Fragmentation' + '' + (maxPayloadNoFrag > 0 ? maxPayloadNoFrag.toFixed(0) + ' bytes' : 'N/A') + '' + 'Effective Throughput' + '' + effectiveThroughput.toFixed(3) + ' Mbps (of ' + bandwidth.toFixed(1) + ' Mbps)' + 'Throughput Loss' + '' + throughputLoss.toFixed(3) + ' Mbps (' + throughputLossPct.toFixed(2) + '%)' + 'Overhead Bandwidth @ ' + pps.toFixed(0) + ' PPS' + '' + overheadBandwidthMbps.toFixed(4) + ' Mbps' + 'Total Encapsulated Bandwidth @ ' + pps.toFixed(0) + ' PPS' + '' + totalBwMbps.toFixed(4) + ' Mbps' + '' + '' + cipherInfo + '

'; }

#### Formulas Used

Encapsulated Packet Size: encap_size = payload_bytes + overhead_bytes

Overhead Percentage: overhead_pct (%) = (overhead_bytes / payload_bytes) × 100

Effective Throughput: effective_throughput (Mbps) = bandwidth × (payload_bytes / encap_size)

Overhead Bandwidth at Given PPS: overhead_bw (Mbps) = (overhead_bytes × 8 × PPS) / 1,000,000

IPsec CBC Padding (average): padding = block_size − (payload mod block_size), minimum 1 byte (block_size = 16 for AES)

#### Assumptions & References

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References

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