commit b6afe7ef236a454d8a6abf104b8846f817378f73
Author: Björn Jacke <bj@sernet.de>
Date:   Thu Oct 15 02:02:30 2009 +0200

    util: cope the all loopback addresses IPv4 knows
    
    The fact that we just recogniced 127.0.0.1 as loopback IP address and not the
    rest of the 127.0.0.0/8 IP address range we used the lo interface for sending
    packages even though we should send them to some more physical interface. This
    way we ended up with failing WINS registration and so on like in #6348.
    On the lo interface sendto() returned "Invalid Argument" (EINVAL).

diff --git a/lib/util/util_net.c b/lib/util/util_net.c
index 0ce495e..0511a28 100644
--- a/lib/util/util_net.c
+++ b/lib/util/util_net.c
@@ -351,13 +351,11 @@ bool is_broadcast_addr(const struct sockaddr *pss)
 }
 
 /**
- * Check if an IPv7 is 127.0.0.1
+ * Check if an IPv4 is in IN_LOOPBACKNET (127.0.0.0/8)
  */
 bool is_loopback_ip_v4(struct in_addr ip)
 {
-	struct in_addr a;
-	a.s_addr = htonl(INADDR_LOOPBACK);
-	return(ip.s_addr == a.s_addr);
+	return ((ntohl(ip.s_addr) & IN_CLASSA_NET) == (IN_LOOPBACKNET << IN_CLASSA_NSHIFT));
 }
 
 /**