MTU (Maximum Transmission Unit)

MTU is the largest packet size a link can carry without fragmentation.

Updated: 2026-03-05

Definition

MTU defines the maximum frame/packet size for a network link (commonly 1500 bytes on Ethernet).

MTU mismatches can cause dropped packets, slow performance, or broken VPNs/tunnels.

Key points

Common Ethernet MTU: 1500
PMTUD helps discover the path MTU
Tunnels/VPNs reduce effective MTU

Common mistakes

Ignoring MTU when troubleshooting VPN or cloud connectivity.
Blocking ICMP and breaking PMTUD.

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