+AC_MSG_CHECKING(whether netdb.h defines uint32_t)
+AC_CACHE_VAL(guile_cv_have_uint32_t,
+[AC_TRY_COMPILE([#include <netdb.h>],
+[uint32_t a;],
+guile_cv_have_uint32_t=yes, guile_cv_have_uint32_t=no)])
+AC_MSG_RESULT($guile_cv_have_uint32_t)
+if test $guile_cv_have_uint32_t = yes; then
+ AC_DEFINE(HAVE_UINT32_T)
+fi
+
+AC_MSG_CHECKING(for working IPv6 support)
+AC_CACHE_VAL(guile_cv_have_ipv6,
+[AC_TRY_COMPILE([#include <netinet/in.h>
+#include <sys/socket.h>],
+[struct sockaddr_in6 a; a.sin6_family = AF_INET6;],
+guile_cv_have_ipv6=yes, guile_cv_have_ipv6=no)])
+AC_MSG_RESULT($guile_cv_have_ipv6)
+if test $guile_cv_have_ipv6 = yes; then
+ AC_DEFINE(HAVE_IPV6)
+fi
+
+# included in rfc2553 but not in older implementations, e.g., glibc 2.1.3.
+AC_MSG_CHECKING(whether sockaddr_in6 has sin6_scope_id)
+AC_CACHE_VAL(guile_cv_have_sin6_scope_id,
+[AC_TRY_COMPILE([#include <netinet/in.h>],
+[struct sockaddr_in6 sok; sok.sin6_scope_id = 0;],
+guile_cv_have_sin6_scope_id=yes, guile_cv_have_sin6_scope_id=no)])
+AC_MSG_RESULT($guile_cv_have_sin6_scope_id)
+if test $guile_cv_have_sin6_scope_id = yes; then
+ AC_DEFINE(HAVE_SIN6_SCOPE_ID)
+fi
+