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diff --git a/src/org/xbill/DNS/ClientSubnetOption.java b/src/org/xbill/DNS/ClientSubnetOption.java
new file mode 100644
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+++ b/src/org/xbill/DNS/ClientSubnetOption.java
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+// Copyright (c) 1999-2004 Brian Wellington (bwelling@xbill.org)
+
+package org.xbill.DNS;
+
+import java.net.*;
+import java.util.regex.*;
+
+/**
+ * The Client Subnet EDNS Option, defined in
+ * http://tools.ietf.org/html/draft-vandergaast-edns-client-subnet-00
+ * ("Client subnet in DNS requests").
+ *
+ * The option is used to convey information about the IP address of the
+ * originating client, so that an authoritative server can make decisions
+ * based on this address, rather than the address of the intermediate
+ * caching name server.
+ *
+ * The option is transmitted as part of an OPTRecord in the additional section
+ * of a DNS message, as defined by RFC 2671 (EDNS0).
+ * 
+ * An option code has not been assigned by IANA; the value 20730 (used here) is
+ * also used by several other implementations.
+ *
+ * The wire format of the option contains a 2-byte length field (1 for IPv4, 2
+ * for IPv6), a 1-byte source netmask, a 1-byte scope netmask, and an address
+ * truncated to the source netmask length (where the final octet is padded with
+ * bits set to 0)
+ * 
+ *
+ * @see OPTRecord
+ * 
+ * @author Brian Wellington
+ * @author Ming Zhou <mizhou@bnivideo.com>, Beaumaris Networks
+ */
+public class ClientSubnetOption extends EDNSOption {
+
+private static final long serialVersionUID = -3868158449890266347L;
+
+private int family;
+private int sourceNetmask;
+private int scopeNetmask;
+private InetAddress address;
+
+ClientSubnetOption() {
+	super(EDNSOption.Code.CLIENT_SUBNET);
+}
+
+private static int
+checkMaskLength(String field, int family, int val) {
+	int max = Address.addressLength(family) * 8;
+	if (val < 0 || val > max)
+		throw new IllegalArgumentException("\"" + field + "\" " + val +
+						   " must be in the range " +
+						   "[0.." + max + "]");
+	return val;
+}
+
+/**
+ * Construct a Client Subnet option.  Note that the number of significant bits in
+ * the address must not be greater than the supplied source netmask.
+ * XXX something about Java's mapped addresses
+ * @param sourceNetmask The length of the netmask pertaining to the query.
+ * In replies, it mirrors the same value as in the requests.
+ * @param scopeNetmask The length of the netmask pertaining to the reply.
+ * In requests, it MUST be set to 0.  In responses, this may or may not match
+ * the source netmask.
+ * @param address The address of the client.
+ */
+public 
+ClientSubnetOption(int sourceNetmask, int scopeNetmask, InetAddress address) {
+	super(EDNSOption.Code.CLIENT_SUBNET);
+
+	this.family = Address.familyOf(address);
+	this.sourceNetmask = checkMaskLength("source netmask", this.family,
+					     sourceNetmask);
+	this.scopeNetmask = checkMaskLength("scope netmask", this.family,
+					     scopeNetmask);
+	this.address = Address.truncate(address, sourceNetmask);
+
+	if (!address.equals(this.address))
+		throw new IllegalArgumentException("source netmask is not " +
+						   "valid for address");
+}
+
+/**
+ * Construct a Client Subnet option with scope netmask set to 0.
+ * @param sourceNetmask The length of the netmask pertaining to the query.
+ * In replies, it mirrors the same value as in the requests.
+ * @param address The address of the client.
+ * @see ClientSubnetOption
+ */
+public 
+ClientSubnetOption(int sourceNetmask, InetAddress address) {
+	this(sourceNetmask, 0, address);
+}
+
+/**
+ * Returns the family of the network address.  This will be either IPv4 (1)
+ * or IPv6 (2).
+ */
+public int 
+getFamily() {
+	return family;
+}
+
+/** Returns the source netmask. */
+public int 
+getSourceNetmask() {
+	return sourceNetmask;
+}
+
+/** Returns the scope netmask. */
+public int 
+getScopeNetmask() {
+	return scopeNetmask;
+}
+
+/** Returns the IP address of the client. */
+public InetAddress 
+getAddress() {
+	return address;
+}
+
+void 
+optionFromWire(DNSInput in) throws WireParseException {
+	family = in.readU16();
+	if (family != Address.IPv4 && family != Address.IPv6)
+		throw new WireParseException("unknown address family");
+	sourceNetmask = in.readU8();
+	if (sourceNetmask > Address.addressLength(family) * 8)
+		throw new WireParseException("invalid source netmask");
+	scopeNetmask = in.readU8();
+	if (scopeNetmask > Address.addressLength(family) * 8)
+		throw new WireParseException("invalid scope netmask");
+
+	// Read the truncated address
+	byte [] addr = in.readByteArray();
+	if (addr.length != (sourceNetmask + 7) / 8)
+		throw new WireParseException("invalid address");
+
+	// Convert it to a full length address.
+	byte [] fulladdr = new byte[Address.addressLength(family)];
+	System.arraycopy(addr, 0, fulladdr, 0, addr.length);
+
+	try {
+		address = InetAddress.getByAddress(fulladdr);
+	} catch (UnknownHostException e) {
+		throw new WireParseException("invalid address", e);
+	}
+
+	InetAddress tmp = Address.truncate(address, sourceNetmask);
+	if (!tmp.equals(address))
+		throw new WireParseException("invalid padding");
+}
+
+void 
+optionToWire(DNSOutput out) {
+	out.writeU16(family);
+	out.writeU8(sourceNetmask);
+	out.writeU8(scopeNetmask);
+	out.writeByteArray(address.getAddress(), 0, (sourceNetmask + 7) / 8);
+}
+
+String 
+optionToString() {
+	StringBuffer sb = new StringBuffer();
+	sb.append(address.getHostAddress());
+	sb.append("/");
+	sb.append(sourceNetmask);
+	sb.append(", scope netmask ");
+	sb.append(scopeNetmask);
+	return sb.toString();
+}
+
+}