diff --git a/headers/private/net/net_datalink.h b/headers/private/net/net_datalink.h
index 12dfef514b..196bed4611 100644
--- a/headers/private/net/net_datalink.h
+++ b/headers/private/net/net_datalink.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2006, Haiku, Inc. All Rights Reserved.
+ * Copyright 2006-2008, Haiku, Inc. All Rights Reserved.
  * Distributed under the terms of the MIT License.
  */
 #ifndef NET_DATALINK_H
@@ -67,7 +67,7 @@ struct net_datalink_module_info {
 					size_t *_length);
 	status_t (*send_data)(struct net_route *route, struct net_buffer *buffer);
 	status_t (*send_datagram)(struct net_protocol *protocol,
-		struct net_domain *domain, struct net_buffer *buffer);
+					struct net_domain *domain, struct net_buffer *buffer);
 
 	bool (*is_local_address)(struct net_domain *domain,
 					const struct sockaddr *address,
@@ -75,7 +75,7 @@ struct net_datalink_module_info {
 					uint32 *_matchedType);
 	net_interface *(*get_interface)(struct net_domain *domain, uint32 index);
 	net_interface *(*get_interface_with_address)(struct net_domain *domain,
-		const struct sockaddr *address);
+					const struct sockaddr *address);
 
 	// routes
 	status_t (*add_route)(struct net_domain *domain,
@@ -85,7 +85,7 @@ struct net_datalink_module_info {
 	struct net_route *(*get_route)(struct net_domain *domain,
 					const struct sockaddr *address);
 	status_t (*get_buffer_route)(struct net_domain *domain,
-		struct net_buffer *buffer, struct net_route **_route);
+					struct net_buffer *buffer, struct net_route **_route);
 	void (*put_route)(struct net_domain *domain, struct net_route *route);
 
 	status_t (*register_route_info)(struct net_domain *domain,
@@ -100,7 +100,7 @@ struct net_address_module_info {
 	module_info info;
 
 	status_t (*copy_address)(const sockaddr *from, sockaddr **to,
-					bool replaceWithZeros /* = false */, const sockaddr *mask /* = NULL*/);
+					bool replaceWithZeros, const sockaddr *mask);
 
 	status_t (*mask_address)(const sockaddr *address, const sockaddr *mask, 
 					sockaddr *result);
@@ -110,7 +110,7 @@ struct net_address_module_info {
 	bool (*equal_addresses_and_ports)(const sockaddr *a, const sockaddr *b);
 	bool (*equal_masked_addresses)(const sockaddr *a, const sockaddr *b, 
 					const sockaddr *mask);
-	bool (*is_empty_address)(const sockaddr *address, bool checkPort /* = true */);
+	bool (*is_empty_address)(const sockaddr *address, bool checkPort);
 
 	int32 (*first_mask_bit)(const sockaddr *mask);
 
@@ -126,6 +126,9 @@ struct net_address_module_info {
 
 	status_t (*set_to)(sockaddr *address, const sockaddr *from);
 	status_t (*set_to_empty_address)(sockaddr *address);
+	status_t (*set_to_defaults)(sockaddr *defaultMask,
+					sockaddr *defaultBroadcast, sockaddr *address,
+					sockaddr *netmask);
 
 	status_t (*update_to)(sockaddr *address, const sockaddr *from);
 
diff --git a/src/add-ons/kernel/network/protocols/ipv4/ipv4_address.cpp b/src/add-ons/kernel/network/protocols/ipv4/ipv4_address.cpp
index ca07a517b8..7ed7956079 100644
--- a/src/add-ons/kernel/network/protocols/ipv4/ipv4_address.cpp
+++ b/src/add-ons/kernel/network/protocols/ipv4/ipv4_address.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007, Haiku, Inc. All Rights Reserved.
+ * Copyright 2006-2008, Haiku, Inc. All Rights Reserved.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
@@ -388,6 +388,55 @@ ipv4_set_to_empty_address(sockaddr *address)
 }
 
 
+static status_t
+ipv4_set_to_defaults(sockaddr *_defaultMask, sockaddr *_defaultBroadcast,
+	sockaddr *_address, sockaddr *_mask)
+{
+	sockaddr_in *defaultMask = (sockaddr_in *)_defaultMask;
+	sockaddr_in *defaultBroadcast = (sockaddr_in *)_defaultBroadcast;
+	sockaddr_in *address = (sockaddr_in *)_address;
+	sockaddr_in *mask = (sockaddr_in *)_mask;
+
+	if (address == NULL || (defaultMask == NULL && defaultBroadcast == NULL))
+		return B_BAD_VALUE;
+
+	in_addr_t net;
+	if (mask == NULL) {
+		// choose default netmask depending on the class of the address
+		net = address->sin_addr.s_addr;
+		if (IN_CLASSA(net)
+			|| (ntohl(net) >> IN_CLASSA_NSHIFT) == IN_LOOPBACKNET) {
+			// class A, or loopback
+			net = IN_CLASSA_NET;
+		} else if (IN_CLASSB(net)) {
+			// class B
+			net = IN_CLASSB_NET;
+		} else {
+			// class C and rest
+			net = IN_CLASSC_NET;
+		}
+	} else
+		net = mask->sin_addr.s_addr;
+
+	if (defaultMask != NULL) {
+		defaultMask->sin_len = sizeof(sockaddr_in);
+		defaultMask->sin_family = AF_INET;
+		defaultMask->sin_port = 0;
+		defaultMask->sin_addr.s_addr = net;
+	}
+
+	if (defaultBroadcast != NULL) {
+		defaultBroadcast->sin_len = sizeof(sockaddr_in);
+		defaultBroadcast->sin_family = AF_INET;
+		defaultBroadcast->sin_port = 0;
+		defaultBroadcast->sin_addr.s_addr = (address->sin_addr.s_addr & net)
+			| ~net;
+	}
+
+	return B_OK;
+}
+
+
 /*!
 	Computes a hash-value of the given addresses \a ourAddress 
 	and \a peerAddress.
@@ -441,6 +490,7 @@ net_address_module_info gIPv4AddressModule = {
 	ipv4_set_port,
 	ipv4_set_to,
 	ipv4_set_to_empty_address,
+	ipv4_set_to_defaults,
 	ipv4_update_to,
 	ipv4_hash_address_pair,
 	ipv4_checksum_address,
diff --git a/src/add-ons/kernel/network/stack/datalink.cpp b/src/add-ons/kernel/network/stack/datalink.cpp
index 1402236c8b..140dd3efad 100644
--- a/src/add-ons/kernel/network/stack/datalink.cpp
+++ b/src/add-ons/kernel/network/stack/datalink.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2006-2007, Haiku, Inc. All Rights Reserved.
+ * Copyright 2006-2008, Haiku, Inc. All Rights Reserved.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
@@ -164,6 +164,26 @@ add_default_routes(net_interface_private *interface, int32 option)
 }
 
 
+sockaddr *
+reallocate_address(sockaddr **_address, uint32 size)
+{
+	sockaddr *address = *_address;
+
+	size = max_c(size, sizeof(struct sockaddr));
+	if (address != NULL && address->sa_len >= size)
+		return address;
+
+	address = (sockaddr *)malloc(size);
+	if (address == NULL)
+		return NULL;
+
+	free(*_address);
+	*_address = address;
+
+	return address;
+}
+
+
 static status_t
 datalink_control_interface(net_domain_private *domain, int32 option,
 	void *value, size_t *_length, size_t expected, bool getByName)
@@ -624,27 +644,32 @@ interface_protocol_control(net_datalink_protocol *_protocol,
 			if (_address == NULL)
 				return B_BAD_VALUE;
 
-			sockaddr *address = *_address;
-			sockaddr *original = address;
-
 			// allocate new address if needed
-			if (address == NULL
-				|| (address->sa_len < request.ifr_addr.sa_len
-					&& request.ifr_addr.sa_len > sizeof(struct sockaddr))) {
-				address = (sockaddr *)malloc(
-					max_c(request.ifr_addr.sa_len, sizeof(struct sockaddr)));
-			}
+			sockaddr *address = reallocate_address(_address,
+				request.ifr_addr.sa_len);
 
 			// copy new address over
 			if (address != NULL) {
 				remove_default_routes(interface, option);
+				memcpy(address, &request.ifr_addr, request.ifr_addr.sa_len);
 
-				if (original != address) {
-					free(original);
-					*_address = address;
+				if (option == SIOCSIFADDR || option == SIOCSIFNETMASK) {
+					// reset netmask and broadcast addresses to defaults
+					sockaddr *netmask = NULL;
+					sockaddr *oldNetmask = NULL;
+					if (option == SIOCSIFADDR) {
+						netmask = reallocate_address(&interface->mask,
+							request.ifr_addr.sa_len);
+					} else
+						oldNetmask = address;
+
+					sockaddr *broadcast = reallocate_address(
+						&interface->destination, request.ifr_addr.sa_len);
+
+					interface->domain->address_module->set_to_defaults(
+						netmask, broadcast, interface->address, oldNetmask);
 				}
 
-				memcpy(address, &request.ifr_addr, request.ifr_addr.sa_len);
 				add_default_routes(interface, option);
 			}