3 files changed, 36 insertions, 6 deletions

diff --git a/src/include/ipxe/in.h b/src/include/ipxe/in.h
index 3044d6316..05a8122ef 100644
--- a/src/include/ipxe/in.h
+++ b/src/include/ipxe/in.h
@@ -33,6 +33,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define IN_IS_MULTICAST( addr ) \
 	( ( (addr) & htonl ( 0xf0000000 ) ) == htonl ( 0xe0000000 ) )
 
+#define IN_IS_SMALL( mask ) ( (mask) & htonl ( 0x00000003 ) )
+
 /**
  * IP address structure
  */
diff --git a/src/include/ipxe/ip.h b/src/include/ipxe/ip.h
index 285be6dcd..b1b5cb2e7 100644
--- a/src/include/ipxe/ip.h
+++ b/src/include/ipxe/ip.h
@@ -64,9 +64,27 @@ struct ipv4_miniroute {
 
 	/** IPv4 address */
 	struct in_addr address;
-	/** Subnet mask */
+	/** Subnet mask
+	 *
+	 * An address with all of these bits in common with our IPv4
+	 * address is in the local subnet.
+	 */
 	struct in_addr netmask;
-	/** Gateway address */
+	/** Host mask
+	 *
+	 * An address in the local subnet with all of these bits set
+	 * to zero represents the network address, and an address in
+	 * the local subnet with all of these bits set to one
+	 * represents the directed broadcast address.  All other
+	 * addresses in the local subnet are valid host addresses.
+	 *
+	 * For most subnets, this is the inverse of the subnet mask.
+	 * In a small subnet (/31 or /32) there is no network address
+	 * or directed broadcast address, and all addresses in the
+	 * subnet are valid host addresses.
+	 */
+	struct in_addr hostmask;
+	/** Gateway address, or zero for no gateway */
 	struct in_addr gateway;
 };
 
diff --git a/src/net/ipv4.c b/src/net/ipv4.c
index b91fa2ad0..5d0cb0f9a 100644
--- a/src/net/ipv4.c
+++ b/src/net/ipv4.c
@@ -85,9 +85,18 @@ static int add_ipv4_miniroute ( struct net_device *netdev,
 				struct in_addr address, struct in_addr netmask,
 				struct in_addr gateway ) {
 	struct ipv4_miniroute *miniroute;
+	struct in_addr hostmask;
+	struct in_addr broadcast;
 
+	/* Calculate host mask */
+	hostmask.s_addr = ( IN_IS_SMALL ( netmask.s_addr ) ?
+			    INADDR_NONE : ~netmask.s_addr );
+	broadcast.s_addr = ( address.s_addr | hostmask.s_addr );
+
+	/* Print debugging information */
 	DBGC ( netdev, "IPv4 add %s", inet_ntoa ( address ) );
 	DBGC ( netdev, "/%s ", inet_ntoa ( netmask ) );
+	DBGC ( netdev, "bc %s ", inet_ntoa ( broadcast ) );
 	if ( gateway.s_addr )
 		DBGC ( netdev, "gw %s ", inet_ntoa ( gateway ) );
 	DBGC ( netdev, "via %s\n", netdev->name );
@@ -103,8 +112,9 @@ static int add_ipv4_miniroute ( struct net_device *netdev,
 	miniroute->netdev = netdev_get ( netdev );
 	miniroute->address = address;
 	miniroute->netmask = netmask;
+	miniroute->hostmask = hostmask;
 	miniroute->gateway = gateway;
-		
+
 	/* Add to end of list if we have a gateway, otherwise
 	 * to start of list.
 	 */
@@ -310,7 +320,7 @@ static int ipv4_tx ( struct io_buffer *iobuf,
 	struct sockaddr_in *sin_dest = ( ( struct sockaddr_in * ) st_dest );
 	struct ipv4_miniroute *miniroute;
 	struct in_addr next_hop;
-	struct in_addr netmask = { .s_addr = 0 };
+	struct in_addr hostmask = { .s_addr = INADDR_NONE };
 	uint8_t ll_dest_buf[MAX_LL_ADDR_LEN];
 	const void *ll_dest;
 	int rc;
@@ -338,7 +348,7 @@ static int ipv4_tx ( struct io_buffer *iobuf,
 	     ( ( miniroute = ipv4_route ( sin_dest->sin_scope_id,
 					  &next_hop ) ) != NULL ) ) {
 		iphdr->src = miniroute->address;
-		netmask = miniroute->netmask;
+		hostmask = miniroute->hostmask;
 		netdev = miniroute->netdev;
 	}
 	if ( ! netdev ) {
@@ -373,7 +383,7 @@ static int ipv4_tx ( struct io_buffer *iobuf,
 		ntohs ( iphdr->chksum ) );
 
 	/* Calculate link-layer destination address, if possible */
-	if ( ( ( next_hop.s_addr ^ INADDR_BROADCAST ) & ~netmask.s_addr ) == 0){
+	if ( ( ( ~next_hop.s_addr ) & hostmask.s_addr ) == 0 ) {
 		/* Broadcast address */
 		ipv4_stats.out_bcast_pkts++;
 		ll_dest = netdev->ll_broadcast;