diff --git a/share/man/man4/lo.4 b/share/man/man4/lo.4
index 86dd47eb597a..12bf79251409 100644
--- a/share/man/man4/lo.4
+++ b/share/man/man4/lo.4
@@ -1,5 +1,7 @@
 .\" Copyright (c) 1983, 1991, 1993
-.\"	The Regents of the University of California.  All rights reserved.
+.\"	The Regents of the University of California.
+.\" Copyright (c) 2009 Robert N. M. Watson
+.\" All rights reserved.
 .\"
 .\" Redistribution and use in source and binary forms, with or without
 .\" modification, are permitted provided that the following conditions
@@ -9,10 +11,6 @@
 .\" 2. Redistributions in binary form must reproduce the above copyright
 .\"    notice, this list of conditions and the following disclaimer in the
 .\"    documentation and/or other materials provided with the distribution.
-.\" 3. All advertising materials mentioning features or use of this software
-.\"    must display the following acknowledgement:
-.\"	This product includes software developed by the University of
-.\"	California, Berkeley and its contributors.
 .\" 4. Neither the name of the University nor the names of its contributors
 .\"    may be used to endorse or promote products derived from this software
 .\"    without specific prior written permission.
@@ -32,7 +30,7 @@
 .\"     @(#)lo.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd June 5, 1993
+.Dd March 15, 2009
 .Dt LO 4
 .Os
 .Sh NAME
@@ -58,6 +56,20 @@ The loopback should
 .Em never
 be configured first unless no hardware
 interfaces exist.
+.Pp
+If the transmit checksum offload capability flag is enabled on a loopback
+interface, checksums will not be generated by IP, UDP, or TCP for packets
+sent on the interface.
+.Pp
+If the receive checksum offload capability flag is enabled on a loopback
+interface, checksums will not be validated by IP, UDP, or TCP for packets
+received on the interface.
+.Pp
+By default, both receive and transmit checksum flags will be enabled, in
+order to avoid the overhead of checksumming for local communication where
+data corruption is unlikely.
+If transmit checksum generation is disabled, then validation should also be
+disabled in order to avoid packets being dropped due to invalid checksums.
 .Sh DIAGNOSTICS
 .Bl -diag
 .It lo%d: can't handle af%d.
@@ -74,8 +86,5 @@ The
 .Nm
 device appeared in
 .Bx 4.2 .
-.Sh BUGS
-Previous versions of the system enabled the loopback interface
-automatically, using a nonstandard Internet address (127.1).
-Use of that address is now discouraged; a reserved host address
-for the local network should be used instead.
+The current checksum generation and validation avoidance policy appeared in
+.Fx 8.0 .
diff --git a/sys/net/if_loop.c b/sys/net/if_loop.c
index d5548fcd935c..3fd003e3c524 100644
--- a/sys/net/if_loop.c
+++ b/sys/net/if_loop.c
@@ -138,6 +138,8 @@ lo_clone_create(struct if_clone *ifc, int unit, caddr_t params)
 	ifp->if_ioctl = loioctl;
 	ifp->if_output = looutput;
 	ifp->if_snd.ifq_maxlen = ifqmaxlen;
+	ifp->if_hwassist = ifp->if_capabilities = ifp->if_capenable =
+	    IFCAP_HWCSUM;
 	if_attach(ifp);
 	bpfattach(ifp, DLT_NULL, sizeof(u_int32_t));
 	if (V_loif == NULL)
@@ -212,6 +214,13 @@ looutput(struct ifnet *ifp, struct mbuf *m, struct sockaddr *dst,
 #if 1	/* XXX */
 	switch (dst->sa_family) {
 	case AF_INET:
+		if (ifp->if_capenable & IFCAP_RXCSUM) {
+			m->m_pkthdr.csum_data = 0xffff;
+			m->m_pkthdr.csum_flags = CSUM_DATA_VALID |
+			    CSUM_PSEUDO_HDR | CSUM_IP_CHECKED |
+			    CSUM_IP_VALID | CSUM_SCTP_VALID;
+		}
+		m->m_pkthdr.csum_flags &= ~(CSUM_IP | CSUM_TCP | CSUM_UDP);
 	case AF_INET6:
 	case AF_IPX:
 	case AF_APPLETALK:
@@ -348,7 +357,7 @@ loioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 {
 	struct ifaddr *ifa;
 	struct ifreq *ifr = (struct ifreq *)data;
-	int error = 0;
+	int error = 0, mask;
 
 	switch (cmd) {
 	case SIOCSIFADDR:
@@ -391,6 +400,18 @@ loioctl(struct ifnet *ifp, u_long cmd, caddr_t data)
 	case SIOCSIFFLAGS:
 		break;
 
+	case SIOCSIFCAP:
+		mask = ifp->if_capenable ^ ifr->ifr_reqcap;
+		if ((mask & IFCAP_RXCSUM) != 0)
+			ifp->if_capenable ^= IFCAP_RXCSUM;
+		if ((mask & IFCAP_TXCSUM) != 0)
+			ifp->if_capenable ^= IFCAP_TXCSUM;
+		if (ifp->if_capenable & IFCAP_TXCSUM)
+			ifp->if_hwassist = CSUM_IP | CSUM_TCP | CSUM_UDP;
+		else
+			ifp->if_hwassist = 0;
+		break;
+
 	default:
 		error = EINVAL;
 	}