Index: head/sys/netinet6/ip6_id.c
===================================================================
--- head/sys/netinet6/ip6_id.c
+++ head/sys/netinet6/ip6_id.c
@@ -89,6 +89,7 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/kernel.h>
+#include <sys/random.h>
 #include <sys/socket.h>
 #include <sys/libkern.h>
 
@@ -257,6 +258,16 @@
 u_int32_t
 ip6_randomflowlabel(void)
 {
+
+	/*
+	 * It's ok to emit zero flow labels early, before random is available
+	 * (seeded).  RFC 6437:
+	 *
+	 * "A Flow Label of zero is used to indicate packets that have not been
+	 * labeled."
+	 */
+	if (__predict_false(!is_random_seeded()))
+		return (0);
 
 	return randomid(&randomtab_20) & 0xfffff;
 }