--- sys/netinet/in.c
+++ sys/netinet/in.c
@@ -34,6 +34,7 @@
 
 #include <sys/cdefs.h>
 #include "opt_inet.h"
+#include "myloop_masklen.h"
 
 #define IN_HISTORICAL_NETS		/* include class masks */
 
--- sys/netinet/in.h
+++ sys/netinet/in.h
@@ -382,12 +382,12 @@
 #define	IN_BADCLASS(i)		(((in_addr_t)(i) & 0xf0000000) == 0xf0000000)
 
 #define IN_LINKLOCAL(i)		(((in_addr_t)(i) & 0xffff0000) == 0xa9fe0000)
+#define IN_LOOPBACK_MASK_DFLT	(INADDR_BROADCAST << (32 - MYLOOP_MASKLEN))
 #ifdef _KERNEL
 #define IN_LOOPBACK(i) \
     (((in_addr_t)(i) & V_in_loopback_mask) == 0x7f000000)
-#define IN_LOOPBACK_MASK_DFLT	0xff000000
 #else
-#define IN_LOOPBACK(i)		(((in_addr_t)(i) & 0xff000000) == 0x7f000000)
+#define IN_LOOPBACK(i)		IN_MY_LOOP(i)	
 #endif
 #define IN_ZERONET(i)		(((in_addr_t)(i) & 0xff000000) == 0)
 
--- sys/netinet/ip_input.c
+++ sys/netinet/ip_input.c
@@ -37,6 +37,7 @@
 #include "opt_ipstealth.h"
 #include "opt_ipsec.h"
 #include "opt_route.h"
+#include "myloop_masklen.h"
 #include "opt_rss.h"
 #include "opt_sctp.h"
 
--- sys/netinet/ip_output.c
+++ sys/netinet/ip_output.c
@@ -38,6 +38,7 @@
 #include "opt_mbuf_stress_test.h"
 #include "opt_ratelimit.h"
 #include "opt_route.h"
+#include "myloop_masklen.h"
 #include "opt_rss.h"
 #include "opt_sctp.h"
 
--- include/myloop_masklen.h
+++ include/myloop_masklen.h
@@ -0,0 +1,7 @@
+#define	MYLOOP_MASKLEN 24
+
+#ifndef MYLOOP_MASKLEN
+#define	IN_MY_LOOP(i)		(((in_addr_t)(i) & IN_CLASSA_NET) == (IN_LOOPBACKNET << IN_CLASSA_NSHIFT))
+#else
+#define	IN_MY_LOOP(i)		(((in_addr_t)(i) & (INADDR_BROADCAST << (32 - MYLOOP_MASKLEN))) == (IN_LOOPBACKNET << IN_CLASSA_NSHIFT))
+#endif
--- sys/myloop_masklen.h
+++ sys/myloop_masklen.h
@@ -0,0 +1,7 @@
+#define	MYLOOP_MASKLEN 24
+
+#ifndef MYLOOP_MASKLEN
+#define	IN_MY_LOOP(i)		(((in_addr_t)(i) & IN_CLASSA_NET) == 0x7F000000)
+#else
+#define	IN_MY_LOOP(i)		(((in_addr_t)(i) & IN_LOOPBACK_MASK_DFLT) == 0x7F000000)
+#endif