Hi Sean,

Thanks for the information. I did some digging too and did find this....for anyone who's new to BSD flavored stacks.

    raw socket with IP_HDRINCL uses different network byteorder for some
        of the IP header fields (ip_off and ip_len).  i think the behavior
        is confusing, and the culprit is 4.[34]BSD. (4.[34]BSD should have
        cleaned it up before supplying this API to users)

        - openbsd:
                rip_input: host byteorder, ip_len is payload length
                rip_output: network byteorder, ip_len is for the whole packet
        - netbsd:
                rip_input: host byteorder, ip_len is payload length
                rip_output: host byteorder, ip_len is for the whole packet
                (same as 4.4BSD, but internally we use network byteorder all
                the way throughout the IPv4 code)
        - freebsd:
                rip_input: host byteorder, ip_len is payload length
                rip_output: host byteorder, ip_len is for the whole packet
                (same as 4.4BSD)

        i think both case should be network byteorder, and ip_len field
        should reflect the length of the whole packet instead of the payload
        length.

-Santosh
> On Sat, Nov 01, 2008 at 08:05:11AM -0400, Santosh Kumar wrote:
> > Hi,
> > 
> > I am looking at a strange problem while receiving RSVP packets. In our 
> system, we send and receive RSVP packets using RAW sockets. The problem we are
>  seeing is this:
> > 
> > Packets are sent properly from the source node and the packets reach the 
> destination. Correctly. We verified that the packet received in our example 
> had totlen field on IP header as 264. However, when we receive the packets 
> through recvfrom interface along with the IP header, the totlen field is now 
> 244 instead of 264. Rest of the header looks good.
> > 
> > The only layer between the point where tcp dump sniffs packet and the 
> application is the iopkt layer. Can someone shed some light on what might be 
> happening here?
> > 
> > Thanks,
> > Santosh
> > 
> 
> See this section of code in rip_input().
> 
> -seanb
> 
> 
> 
> 
>  /*
>   * XXX Compatibility: programs using raw IP expect ip_len
>   * XXX to have the header length subtracted, and in host order.
>   * XXX ip_off is also expected to be host order.
>   */
>  ip->ip_len = ntohs(ip->ip_len) - (ip->ip_hl << 2);
>  NTOHS(ip->ip_off);
> 
>