ICMP fragmentation

Unanswered Question
Oct 29th, 2007

While troubleshooting a problem with a device, I was pinging using a data size of 1600 (ping -l 1600), which just timed out. But pinging other devices on same subnet, ping -l 1600 works fine. This leads me to believe ICMP packets are not blocked anyhwere, but why do some devices fail to return a ping above the standard mtu settings. Device is question is a card reader, but I've also notices jet direct cards will also not return a ping at 1600.

Any insite would be appreciated.

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Edison Ortiz Tue, 10/30/2007 - 18:25

The standard Ethernet frame-size is 1500. It's up to the source/destination device to support packets greater that 1500.

Based on your test, the source device supports it (not sure if this was a switch/router/workstation) but only selected destination devices did.

The card reader and old Jet Direct cards are good example of devices that due to their age, won't support packets larger than 1500.

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