Ping Command Packet Size Differences Across Vendors
When troubleshooting MTU and ICMP reachability across vendor platforms, understanding how each calculates the ping packet size is critical. Cisco, Juniper, and PC operating systems all interpret the ping size parameter differently, leading to different on-wire packet lengths. Cisco In Cisco, the ping size parameter specifies the total packet size including the IP header (20 bytes) and ICMP header (8 bytes). The data payload is what remains. The encapsulation headers added by the egress interface will be included on top of this size. Importantly, the MTU command under an interface specifies the L2 payload size — the maximum data + IP + ICMP that the interface will forward. So if you set MTU 1500 on an Ethernet interface, the on-wire frame size will be 1500 + 14 bytes (Ethernet header) = 1514 bytes. For VLAN-tagged frames, add another 4 bytes (802.1Q tag). ...