--- /sys/net/if_loop.c	2010-06-02 17:47:35.000000000 +0200
+++ if_loop.c	2011-03-06 03:00:22.000000000 +0100
@@ -27,7 +27,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)if_loop.c	8.2 (Berkeley) 1/9/95
- * $FreeBSD: src/sys/net/if_loop.c,v 1.140.2.2 2010/05/31 22:18:42 rwatson Exp $
+ * $FreeBSD: src/sys/net/if_loop.c,v 1.140.2.2.4.1 2010/12/21 17:09:25 kensmith Exp $
  */
 
 /*
@@ -58,9 +58,15 @@
 #include <net/bpf.h>
 #include <net/vnet.h>
 
+#define LO_FLOWID
+
 #ifdef	INET
 #include <netinet/in.h>
 #include <netinet/in_var.h>
+#ifdef LO_FLOWID
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+#endif
 #endif
 
 #ifdef IPX
@@ -207,6 +213,28 @@
 
 DECLARE_MODULE(if_lo, loop_mod, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY);
 
+#ifdef LO_FLOWID
+static u_int
+losimflowid(struct mbuf *m)
+{
+	u_int flowid = 0;
+#ifdef INET
+	struct ip *ip = NULL;
+	struct tcphdr *th;
+	
+	ip = mtod(m, struct ip *);
+	flowid = ip->ip_src.s_addr ^ ip->ip_dst.s_addr;
+
+	if (ip->ip_p == IPPROTO_TCP) {
+		/* XXX: th offset may not be correct */
+		th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2));
+		flowid |= (th->th_dport << 16) | th->th_sport;
+	}
+#endif
+	return (flowid);
+}
+#endif
+
 int
 looutput(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
     struct route *ro)
@@ -252,6 +280,10 @@
 			m->m_pkthdr.csum_flags = LO_CSUM_SET;
 		}
 		m->m_pkthdr.csum_flags &= ~LO_CSUM_FEATURES;
+#ifdef LO_FLOWID
+		m->m_flags |= M_FLOWID;
+		m->m_pkthdr.flowid = losimflowid(m);
+#endif
 	case AF_INET6:
 	case AF_IPX:
 	case AF_APPLETALK: