senol

hi. i am currently studying on socket programmng .for this aim i bought stevens network programming book . i downloaded source codes of the volueme 1 and also aoutoconf tool .i did all the commands in readme file of unpv12e directory which includes source codes but when i make lib it gives an error like this "redefination of struct in_pktinfo" in unp.h . what should i do? .thank you for your help