diff --git a/lib/isc/unix/net.c b/lib/isc/unix/net.c
new file mode 100644
index 0000000000..9ab9b6946f
--- /dev/null
+++ b/lib/isc/unix/net.c
@@ -0,0 +1,92 @@
+/*
+ * Copyright (C) 1999  Internet Software Consortium.
+ * 
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
+ * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
+ * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+ * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+ * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
+ * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+ * SOFTWARE.
+ */
+
+#include <config.h>
+
+#include <errno.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <isc/assertions.h>
+#include <isc/error.h>
+#include <isc/net.h>
+#include <isc/once.h>
+
+static isc_once_t 	once = ISC_ONCE_INIT;
+static isc_result_t	ipv4_result = ISC_R_NOTFOUND;
+static isc_result_t	ipv6_result = ISC_R_NOTFOUND;
+
+static isc_result_t
+try_proto(int domain) {
+	int s;
+
+	s = socket(domain, SOCK_STREAM, 0);
+	if (s == -1) {
+		switch (errno) {
+#ifdef EAFNOSUPPORT
+		case EAFNOSUPPORT:
+#endif
+#ifdef EINVAL
+		case EINVAL:
+#endif
+			return (ISC_R_NOTFOUND);
+		default:
+			UNEXPECTED_ERROR(__FILE__, __LINE__,
+					 "socket() failed: %s",
+					 strerror(errno));
+			return (ISC_R_UNEXPECTED);
+		}
+	}
+	close (s);
+
+	return (ISC_R_SUCCESS);
+}
+
+static void
+initialize_action(void) {
+	ipv4_result = try_proto(PF_INET);
+#ifdef ISC_NET_HAVEIPV6
+	ipv6_result = try_proto(PF_INET6);
+#endif
+}
+
+static void
+initialize(void) {
+	RUNTIME_CHECK(isc_once_do(&once, initialize_action) == ISC_R_SUCCESS);
+}
+
+isc_result_t
+isc_net_haveipv4(void) {
+
+	/*
+	 * Check if the system's kernel supports IPv4.
+	 */
+
+	initialize();
+	return (ipv4_result);
+}
+
+isc_result_t
+isc_net_haveipv6(void) {
+
+	/*
+	 * Check if the system's kernel supports IPv6.
+	 */
+
+	initialize();
+	return (ipv6_result);
+}