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MTU Size Tester - Test Maximum Transmission Unit for Network Optimization

MTU Size Tester

Test the Maximum Transmission Unit (MTU) to identify the optimal packet size for your network connection.

What is MTU (Maximum Transmission Unit)?

MTU is the largest size packet or frame that can be sent in a single network transaction. If a packet exceeds the MTU, it must be fragmented into smaller packets, which can reduce network efficiency and performance. Finding the optimal MTU ensures efficient data transmission without fragmentation.

Common MTU Sizes:

  • 1500 bytes: Standard Ethernet MTU (most common)
  • 1492 bytes: PPPoE connections (DSL)
  • 1472 bytes: Common for VPN tunnels
  • 1280 bytes: Minimum IPv6 MTU
  • 9000 bytes: Jumbo frames (high-performance networks)

Why Test MTU?

  • Optimize Performance: Avoid packet fragmentation and retransmissions
  • VPN Configuration: Set proper MTU for VPN tunnels
  • Gaming: Reduce latency by using optimal packet sizes
  • Streaming: Improve video/audio streaming quality
  • Troubleshooting: Diagnose connectivity issues related to packet size

How to Use the MTU Tester

Step 1: Enter a hostname (e.g., google.com) or IP address (e.g., 8.8.8.8)
Step 2: Click "Test MTU" to start testing various packet sizes
Step 3: Review the results to find the largest successful packet size
Step 4: Use the optimal MTU value to configure your network settings

Understanding Test Results:

The tool tests common MTU sizes from largest to smallest. The optimal MTU is the largest packet size that successfully reaches the destination without fragmentation. Packets marked as "Failed" exceeded the path MTU and would require fragmentation.

How to Set MTU (Examples):

Windows:
netsh interface ipv4 set subinterface "Ethernet" mtu=1472

Linux:
sudo ip link set dev eth0 mtu 1472

macOS:
sudo ifconfig en0 mtu 1472

Router/Firewall:
Configure MTU in device web interface or CLI

MTU Calculation:

Formula: MTU = Maximum packet size + IP header (20 bytes) + ICMP header (8 bytes)
Example: If 1472 bytes succeeds, MTU = 1472 + 20 + 8 = 1500 bytes

Common MTU Issues:

  • Black Hole Router: Router silently drops large packets without ICMP notification
  • VPN MTU: VPN adds overhead, reducing effective MTU
  • Path MTU Discovery: Some firewalls block ICMP, preventing MTU detection
  • Jumbo Frames: All devices must support same MTU for jumbo frames

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