001 /*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements. See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership. The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License. You may obtain a copy of the License at
009 *
010 * http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied. See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 *
019 */
020
021 package org.apache.directory.server.dns.io.encoder;
022
023
024 /**
025 * 4. NAPTR RR Format
026 *
027 * 4.1 Packet Format
028 *
029 * The packet format of the NAPTR RR is given below. The DNS type code
030 * for NAPTR is 35.
031 *
032 * The packet format for the NAPTR record is as follows
033 * 1 1 1 1 1 1
034 * 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
035 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
036 * | ORDER |
037 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
038 * | PREFERENCE |
039 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
040 * / FLAGS /
041 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
042 * / SERVICES /
043 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
044 * / REGEXP /
045 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
046 * / REPLACEMENT /
047 * / /
048 * +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
049 *
050 * <character-string> and <domain-name> as used here are defined in RFC
051 * 1035 [7].
052 *
053 * ORDER
054 * A 16-bit unsigned integer specifying the order in which the NAPTR
055 * records MUST be processed in order to accurately represent the
056 * ordered list of Rules. The ordering is from lowest to highest.
057 * If two records have the same order value then they are considered
058 * to be the same rule and should be selected based on the
059 * combination of the Preference values and Services offered.
060 *
061 * PREFERENCE
062 * Although it is called "preference" in deference to DNS
063 * terminology, this field is equivalent to the Priority value in the
064 * DDDS Algorithm. It is a 16-bit unsigned integer that specifies
065 * the order in which NAPTR records with equal Order values SHOULD be
066 * processed, low numbers being processed before high numbers. This
067 * is similar to the preference field in an MX record, and is used so
068 * domain administrators can direct clients towards more capable
069 * hosts or lighter weight protocols. A client MAY look at records
070 * with higher preference values if it has a good reason to do so
071 * such as not supporting some protocol or service very well.
072 *
073 * The important difference between Order and Preference is that once
074 * a match is found the client MUST NOT consider records with a
075 * different Order but they MAY process records with the same Order
076 * but different Preferences. The only exception to this is noted in
077 * the second important Note in the DDDS algorithm specification
078 * concerning allowing clients to use more complex Service
079 * determination between steps 3 and 4 in the algorithm. Preference
080 * is used to give communicate a higher quality of service to rules
081 * that are considered the same from an authority standpoint but not
082 * from a simple load balancing standpoint.
083 *
084 * It is important to note that DNS contains several load balancing
085 * mechanisms and if load balancing among otherwise equal services
086 * should be needed then methods such as SRV records or multiple A
087 * records should be utilized to accomplish load balancing.
088 *
089 * FLAGS
090 * A <character-string> containing flags to control aspects of the
091 * rewriting and interpretation of the fields in the record. Flags
092 * are single characters from the set A-Z and 0-9. The case of the
093 * alphabetic characters is not significant. The field can be empty.
094 *
095 * It is up to the Application specifying how it is using this
096 * Database to define the Flags in this field. It must define which
097 * ones are terminal and which ones are not.
098 *
099 * SERVICES
100 * A <character-string> that specifies the Service Parameters
101 * applicable to this this delegation path. It is up to the
102 * Application Specification to specify the values found in this
103 * field.
104 *
105 * REGEXP
106 * A <character-string> containing a substitution expression that is
107 * applied to the original string held by the client in order to
108 * construct the next domain name to lookup. See the DDDS Algorithm
109 * specification for the syntax of this field.
110 *
111 * As stated in the DDDS algorithm, The regular expressions MUST NOT
112 * be used in a cumulative fashion, that is, they should only be
113 * applied to the original string held by the client, never to the
114 * domain name produced by a previous NAPTR rewrite. The latter is
115 * tempting in some applications but experience has shown such use to
116 * be extremely fault sensitive, very error prone, and extremely
117 * difficult to debug.
118 *
119 * REPLACEMENT
120 * A <domain-name> which is the next domain-name to query for
121 * depending on the potential values found in the flags field. This
122 * field is used when the regular expression is a simple replacement
123 * operation. Any value in this field MUST be a fully qualified
124 * domain-name. Name compression is not to be used for this field.
125 *
126 * This field and the REGEXP field together make up the Substitution
127 * Expression in the DDDS Algorithm. It is simply a historical
128 * optimization specifically for DNS compression that this field
129 * exists. The fields are also mutually exclusive. If a record is
130 * returned that has values for both fields then it is considered to
131 * be in error and SHOULD be either ignored or an error returned.
132 *
133 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
134 * @version $Rev: 501160 $, $Date: 2007-01-29 21:41:33 +0200 (Mon, 29 Jan 2007) $
135 */
136 public class NameAuthorityPointerEncoder
137 {
138 }