Strange tcpdump file

From: Lindsay (lmf1tat_private)
Date: Sat Oct 20 2001 - 13:05:56 PDT

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    In the several years I've been using tcpdump to capture interesting
    packets, the filter
    "not ( ip proto icmp or ip proto tcp or ip proto udp )"
    had never logged anything. Until I found the following "packet" capture:
    Ethereal version 0.8.20 shows that the packet has IP header length of 0.
    Interestingly, the capture is 1460 bytes in length (less than the
    1500-byte snap length), and it just so happens that stepping into the
    zero-length header (!) shows the packet-length field to be 0x05b4 or
    1460. It seems that tcpdump (version 3.4) / libpcap (version 0.4)
    interprets (some) IP header fields even though the header length is
    I've tried to replicate the packet by revisiting the web sites I had
    visited just before the anomalous packet, but no luck. Snort was silent,
    as was ipchains. Has anybody an idea of what this is? I don't see how it
    could possibly be routed, so I tend to think ...  just a hiccough, noise
    on the line, whatever....
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