Re: tcpdump and BPF filters

[Guy Harris <guy () alum mit edu>]

On Jul 10, 2011, at 6:57 PM, Geoffrey Sisson wrote:

> The catch is that domain names comprise a variable number of
> variable-length fields.

...and include pointers back to other labels, for compression.

If the queries you're can be expressed in a syntax that could be added to the libpcap filter syntax, libpcap could be 
extended to generate BPF programs to match DNS labels (although if those programs loop, they will have to be run in 
userland), which would allow all pcap-based programs, not just tcpdump, to use them.
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