Juniper: “Out IP truncated-ip” messages seen in TCPDUMP

On certain interfaces we may see messages for Out IP truncated-ip when running monitor traffic interface. These are non-impacting in nature; this article describes how to eliminate them by increasing the default capture-size.

Various interfaces insert a different amount of meta information between the packet header and the packet content, so it may happen that on interface type A you get to capture more payload data than on interface type B. These messages can be seen starting with Junos OS 8.0, when BPF kernel extensions were implemented. As can be seen below, with default capture size of 96, Out IP truncated-ip messages are reported:

These messages do not impact performance. Increase the capture size and the the messages will not be seen.

For example:


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