Обяснение на настройката MTU: Подобряване на скоростта на VPN

What is MTU and how is it measured?

MTU stands for Maximum Transmission Unit — the largest size in bytes of a network packet that can be transmitted without fragmentation. On Ethernet networks the typical MTU is 1500 bytes. MTU is measured in bytes and applies to each hop on the network path; the effective MTU for a connection is the smallest MTU of all hops between sender and receiver.

• Packet size unit: bytes
• Common defaults: Ethernet 1500, PPPoE 1492
• VPN tunnels: lower effective MTU due to encapsulation overhead

Why MTU matters for VPNs

VPNs wrap original packets in additional headers (encryption, tunneling) which increases packet size. If the combined size exceeds the path MTU, routers fragment the packet or drop it if fragmentation is disallowed, causing performance and reliability issues.

Key reasons MTU matters:

• Reduced fragmentation: Proper MTU prevents the need to split packets, reducing CPU work and latency.
• Improved throughput: Larger effective payload per packet increases efficiency; but too large causes retransmissions.
• Lower latency and fewer retransmits: Avoiding fragmentation reduces packet loss and retransmit penalties.
• Compatibility: Some networks or firewalls block fragmented packets, causing connection issues.

Benefits of optimizing MTU for VPN use:

• Smoother streaming and gaming latency
• More stable file transfers over VPN
• Fewer connection drops and application timeouts

How MTU affects Free VPN Grass performance on Android

Free VPN Grass encrypts and encapsulates your traffic. On Android, this increases the packet overhead that must fit inside the path MTU. If the MTU is not adjusted to account for encryption overhead, the consequences include:

1. Packet fragmentation across mobile or Wi‑Fi networks.
2. Increased latency as fragmented packets are reassembled.
3. Lower effective throughput due to extra headers and retransmissions.
4. Application errors when packets are dropped (common with large HTTP uploads or game traffic).

Typical scenarios on Android with Free VPN Grass:

• Mobile data networks: Cellular carriers sometimes have lower MTU or middleboxes that mishandle fragmentation — reducing MTU helps.
• Wi‑Fi networks and public hotspots: Shared networks with strict firewalls may drop fragmented packets; reducing MTU avoids issues.
• High-latency links: Smaller MTU can reduce retransmission overhead and improve perceived responsiveness.

Bottom line: adjusting MTU on Android to account for Free VPN Grass’s tunnel overhead often yields faster and more reliable VPN connections.

How to check and change MTU on Android for Free VPN Grass

Note: Free VPN Grass may include automatic MTU/path-MTU discovery. Check the app’s advanced or troubleshooting settings before manual changes.

Best MTU settings and troubleshooting

There is no one-size-fits-all MTU. However, these guidelines work well in most Android + VPN scenarios:

• Default starting point: 1400–1460 for most VPNs (balance between overhead and fragmentation)
• OpenVPN (UDP/TCP): aim for 1400–1450
• WireGuard: can often use 1420–1460 due to smaller overhead
• Cellular/Carrier networks: try 1400 or lower if you see fragmentation

Troubleshooting checklist

1. Verify path MTU with ping tests from a PC on the same network.
2. Test with and without the VPN to isolate whether issues are due to tunnel overhead.
3. Try switching VPN protocol (UDP vs TCP) — UDP is more efficient but sensitive to MTU.
4. Check router and hotspot MTU settings if Android cannot be changed directly.
5. Enable or disable TCP MSS clamping on routers to automatically adjust segments for TCP flows.

MTU comparison table

Quick reference for common MTU values and their impact: