Seems like IRIX 6.5 and Tru64 UNIX 5.1 don't have IPV6_ADD_MEMBERSHIP. They do have IP_ADD_MEMBERSHIP though. Should we just: #ifndef IPV6_ADD_MEMBERSHIP #define IPV6_ADD_MEMBERSHIP IP_ADD_MEMBERSHIP #endif cc -DHAVE_CONFIG_H -I. -I. -I.. -DPATH_SYSCONFDIR=\"/etc/opt/TWWfsw/syslogng1911\" -DPATH_LOCALSTATEDIR=\"/var/opt/TWWfsw/syslogng1911\" -I/opt/TWWfsw/libglib26/include -I/opt/TWWfsw/libglib26/lib/include -I/opt/TWWfsw/gettext014/include -I/opt/TWWfsw/syslogng198/include/eventlog -D_GNU_SOURCE -Wl,-woff,84 -Wl,-woff,85 -woff 1009,1429 -use_readonly_const -G0 -rdata_shared -DEBUG:optimize_space=ON -O2 -OPT:Olimit=0 -c afinet.c cc-1020 cc: ERROR File = afinet.c, Line = 190 The identifier "IPV6_ADD_MEMBERSHIP" is undefined. setsockopt(fd, IPPROTO_IPV6, IPV6_ADD_MEMBERSHIP, &mreq6, sizeof(mreq6)); ^ 1 error detected in the compilation of "afinet.c". -- albert chin (china@thewrittenword.com)