checksums calculated by libnet

Hi,

   suppose i set the checksum field to 0 in libnet_build_tcp and also 0 in
libnet_build_ipv4. now i call libnet_build_tcp first and then i call libnet
build ipv4, here is the checksum calculated properly, i ask this because
when libnet_build_tcp is called it does not have the pseudo header and
hence cant calculate the checksum properly , so does it wait and adds the
checksum just before doing a write for all protocols ??

thanks
Amit
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