Why isn't 'ether proto \ip host host' a legal tcpdump expression?

Posted by Ezequiel Garzon on Server Fault See other posts from Server Fault or by Ezequiel Garzon
Published on 2012-10-13T12:57:21Z Indexed on 2012/10/13 21:40 UTC
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networking

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tcpdump

In its description of valid tcpdump expressions, the pcap-filter man pages state:

The filter expression consists of one or more primitives. Primitives usually consist of an id (name or number) preceded by one or more qualifiers.

In turn, these qualifiers are type, dir and proto. So far so good, but further down we find this:

     ip host host
which is equivalent to:
     ether proto \ip and host host

In the first case, ip and host are, respectively, proto and type. What pattern does ether proto \ip follow? Isn't that, as a whole, a proto qualifier? If so, why isn't (a properly escaped) 'ether proto \ip host host' legal (no and)?

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