Re: inquiry on variable insertion on tcpdump code

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

Ignacio, Domingo Jr Ostria - igndo001 wrote:

> I  inserted a new variable, srtt, into  the print_tcp.h header file  and
> tcp.c source code.

(Presumably you meant "tcp.h header file and print-tcp.c source code".)

If you inserted it into the "struct tcphdr" structure, that's a mistake. 
 That structure *MUST* look like the 20-byte fixed-length portion of 
the TCP header, as specified in RFC 793, as it's used by the print-tcp.c 
code to dissect the TCP header in captured TCP packets.  There's no SRTT 
field in the TCP header, so you can't put an SRTT field into that 
structure (unless the traffic is going between two hosts whose TCP 
implementations have been modified to add such a field to the header - 
but if that's the case, those two hosts will not be able to use TCP to 
communicate with any unmodified hosts, i.e. they won't be able to use 
any TCP-based protocol with any other computers).
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