On Tue, Mar 12, 2002 at 07:44:10PM -0500, Ashley Thomas wrote:
> What is the minimum capture length of an ethernet packet i need
> to do the most important analysis of a packet.

That depends on what you mean by "most important".

If, for example, you're trying to solve an NFS problem, the most
important analysis requires more than the link-layer+IP+TCP header -
and, for some problems, might require the entire (consider
trying to analyze an NFS READDIR/READDIRPLUS reply, for example).

> ethernet - 14 bytes +
> ip       - 20 (upto 60)
> tcp      - 20
> 
> these would contain all the fileds required for doing the filtering
> similar to tcpdump.

Yes, but that's not necessarily all you'd need.

> does tcpdump do filtering on transport layer payload
> ?? or appl data ?

No, but it certainly *prints* data beyond the transport-layer header. 

> so if the capture length is 54 (or 94) we can do all the packet analysis ?

Only if you don't plan to analyze anything past the TCP header.
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