Re: TCP Checksum Calculation

[Brian Haley]

Michael Faber (Diplomand bei Alexander Zimmermann) wrote:
i am doing a modification to the TCP protocol and want to use an
additional bit of the TCP header's Reserved field. I chose to use the
bit next to the Bits used by the ECN mechanism. Therefore i changed the
TCP header definition in include/linux/tcp.h of a 2.6.16.29 Kernel to
struct tcphdr {
        __u16   source;
        __u16   dest;
        __u32   seq;
        __u32   ack_seq;
#if defined(__LITTLE_ENDIAN_BITFIELD)
        __u16   res1:3,
                doff:4,
                fin:1,
                syn:1,
                rst:1,
                psh:1,
                ack:1,
                urg:1,
                ece:1,
                cwr:1,
                elcn:1;

Try putting elcn as the first element in the little endian version, 
where you put it completely changes the TCP header layout.

-Brian
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