--- wikisrc/guide/dns.mdwn 2019/09/02 20:48:36 1.5
+++ wikisrc/guide/dns.mdwn 2021/04/12 13:15:02 1.6
@@ -1,859 +1,2 @@
-**Contents**
-
-[[!toc levels=3]]
-
-# The Domain Name System
-
-Use of the Domain Name System has been discussed in previous chapters, without
-going into detail on the setup of the server providing the service. This chapter
-describes setting up a simple, small domain with one Domain Name System (DNS)
-nameserver on a NetBSD system. It includes a brief explanation and overview of
-the DNS; further information can be obtained from the DNS Resources Directory
-(DNSRD) at .
-
-## DNS Background and Concepts
-
-The DNS is a widely used *naming service* on the Internet and other TCP/IP
-networks. The network protocols, data and file formats, and other aspects of the
-DNS are Internet Standards, specified in a number of RFC documents, and
-described by a number of other reference and tutorial works. The DNS has a
-distributed, client-server architecture. There are reference implementations for
-the server and client, but these are not part of the standard. There are a
-number of additional implementations available for many platforms.
-
-### Naming Services
-
-Naming services are used to provide a mapping between textual names and
-configuration data of some form. A *nameserver* maintains this mapping, and
-clients request the nameserver to *resolve* a name into its attached data.
-
-The reader should have a good understanding of basic hosts to IP address mapping
-and IP address class specifications, see
-[[Name Service Concepts|guide/net-intro#nsconcepts]].
-
-In the case of the DNS, the configuration data bound to a name is in the form of
-standard *Resource Records* (RRs). These textual names conform to certain
-structural conventions.
-
-### The DNS namespace
-
-The DNS presents a hierarchical name space, much like a UNIX filesystem,
-pictured as an inverted tree with the *root* at the top.
-
- TOP-LEVEL .org
- |
- MID-LEVEL .diverge.org
- ______________________|________________________
- | | |
- BOTTOM-LEVEL strider.diverge.org samwise.diverge.org wormtongue.diverge.org
-
-The system can also be logically divided even further if one wishes at different
-points. The example shown above shows three nodes on the diverge.org domain, but
-we could even divide diverge.org into subdomains such as
-"strider.net1.diverge.org", "samwise.net2.diverge.org" and
-"wormtongue.net2.diverge.org"; in this case, 2 nodes reside in
-"net2.diverge.org" and one in "net1.diverge.org".
-
-There are directories of names, some of which may be sub-directories of further
-names. These directories are sometimes called *zones*. There is provision for
-symbolic links, redirecting requests for information on one name to the records
-bound to another name. Each name recognised by the DNS is called a *Domain
-Name*, whether it represents information about a specific host, or a directory
-of subordinate Domain Names (or both, or something else).
-
-Unlike most filesystem naming schemes, however, Domain Names are written with
-the innermost name on the left, and progressively higher-level domains to the
-right, all the way up to the root directory if necessary. The separator used
-when writing Domain Names is a period, ".".
-
-Like filesystem pathnames, Domain Names can be written in an absolute or
-relative manner, though there are some differences in detail. For instance,
-there is no way to indirectly refer to the parent domain like with the UNIX `..`
-directory. Many (but not all) resolvers offer a search path facility, so that
-partially-specified names can be resolved relative to additional listed
-sub-domains other than the client's own domain. Names that are completely
-specified all the way to the root are called *Fully Qualified Domain Names* or
-*FQDN*s. A defining characteristic of an FQDN is that it is written with a
-terminating period. The same name, without the terminating period, may be
-considered relative to some other sub-domain. It is rare for this to occur
-without malicious intent, but in part because of this possibility, FQDNs are
-required as configuration parameters in some circumstances.
-
-On the Internet, there are some established conventions for the names of the
-first few levels of the tree, at which point the hierarchy reaches the level of
-an individual organisation. This organisation is responsible for establishing
-and maintaining conventions further down the tree, within its own domain.
-
-### Resource Records
-
-Resource Records for a domain are stored in a standardised format in an ASCII
-text file, often called a *zone file*. The following Resource Records are
-commonly used (a number of others are defined but not often used, or no longer
-used). In some cases, there may be multiple RR types associated with a name, and
-even multiple records of the same type.
-
-#### Common DNS Resource Records
-
- * *A: Address* -- This record contains the numerical IP address associated with
- the name.
-
- * *CNAME: Canonical Name* -- This record contains the Canonical Name (an FQDN
- with an associated A record) of the host name to which this record is bound.
- This record type is used to provide name aliasing, by providing a link to
- another name with which other appropriate RR's are associated. If a name has
- a CNAME record bound to it, it is an alias, and no other RR's are permitted
- to be bound to the same name.
-
- It is common for these records to be used to point to hosts providing a
- particular service, such as an FTP or HTTP server. If the service must be
- moved to another host, the alias can be changed, and the same name will reach
- the new host.
-
- * *PTR: Pointer* -- This record contains a textual name. These records are
- bound to names built in a special way from numerical IP addresses, and are
- used to provide a reverse mapping from an IP address to a textual name. This
- is described in more detail in [[Reverse Resolution|guide/dns#bg-reverse]].
-
- * *NS: Name Server* -- This record type is used to *delegate* a sub-tree of the
- Domain Name space to another nameserver. The record contains the FQDN of a
- DNS nameserver with information on the sub-domain, and is bound to the name
- of the sub-domain. In this manner, the hierarchical structure of the DNS is
- established. Delegation is described in more detail in
- [[Delegation|guide/dns#bg-delegation]].
-
- * *MX: Mail eXchange* -- This record contains the FQDN for a host that will
- accept SMTP electronic mail for the named domain, together with a priority
- value used to select an MX host when relaying mail. It is used to indicate
- other servers that are willing to receive and spool mail for the domain if
- the primary MX is unreachable for a time. It is also used to direct email to
- a central server, if desired, rather than to each and every individual
- workstation.
-
- * *HINFO: Host Information* -- Contains two strings, intended for use to
- describe the host hardware and operating system platform. There are defined
- strings to use for some systems, but their use is not enforced. Some sites,
- because of security considerations, do not publicise this information.
-
- * *TXT: Text* -- A free-form text field, sometimes used as a comment field,
- sometimes overlaid with site-specific additional meaning to be interpreted by
- local conventions.
-
- * *SOA: Start of Authority* -- This record is required to appear for each zone
- file. It lists the primary nameserver and the email address of the person
- responsible for the domain, together with default values for a number of
- fields associated with maintaining consistency across multiple servers and
- caching of the results of DNS queries.
-
-### Delegation
-
-Using NS records, authority for portions of the DNS namespace below a certain
-point in the tree can be delegated, and further sub-parts below that delegated
-again. It is at this point that the distinction between a domain and a zone
-becomes important. Any name in the DNS is called a domain, and the term applies
-to that name and to any subordinate names below that one in the tree. The
-boundaries of a zone are narrower, and are defined by delegations. A zone starts
-with a delegation (or at the root), and encompasses all names in the domain
-below that point, excluding names below any subsequent delegations.
-
-This distinction is important for implementation - a zone is a single
-administrative entity (with a single SOA record), and all data for the zone is
-referred to by a single file, called a *zone file*. A zone file may contain more
-than one period-separated level of the namespace tree, if desired, by including
-periods in the names in that zone file. In order to simplify administration and
-prevent overly-large zone files, it is quite legal for a DNS server to delegate
-to itself, splitting the domain into several zones kept on the same server.
-
-### Delegation to multiple servers
-
-For redundancy, it is common (and often administratively required) that there be
-more than one nameserver providing information on a zone. It is also common that
-at least one of these servers be located at some distance (in terms of network
-topology) from the others, so that knowledge of that zone does not become
-unavailable in case of connectivity failure. Each nameserver will be listed in
-an NS record bound to the name of the zone, stored in the parent zone on the
-server responsible for the parent domain. In this way, those searching the name
-hierarchy from the top down can contact any one of the servers to continue
-narrowing their search. This is occasionally called *walking the tree*.
-
-There are a number of nameservers on the Internet which are called *root
-nameservers*. These servers provide information on the very top levels of the
-domain namespace tree. These servers are special in that their addresses must be
-pre-configured into nameservers as a place to start finding other servers.
-Isolated networks that cannot access these servers may need to provide their own
-root nameservers.
-
-### Secondaries, Caching, and the SOA record
-
-In order to maintain consistency between these servers, one is usually
-configured as the *primary* server, and all administrative changes are made on
-this server. The other servers are configured as *secondaries*, and transfer the
-contents of the zone from the primary. This operational model is not required,
-and if external considerations require it, multiple primaries can be used
-instead, but consistency must then be maintained by other means. DNS servers
-that store Resource Records for a zone, whether they be primary or secondary
-servers, are said to be *authoritative* for the zone. A DNS server can be
-authoritative for several zones.
-
-When nameservers receive responses to queries, they can *cache* the results.
-This has a significant beneficial impact on the speed of queries, the query load
-on high-level nameservers, and network utilisation. It is also a major
-contributor to the memory usage of the nameserver process.
-
-There are a number of parameters that are important to maintaining consistency
-amongst the secondaries and caches. The values for these parameters for a
-particular domain zone file are stored in the SOA record. These fields are:
-
-#### Fields of the SOA Record
-
- * *Serial* -- A serial number for the zone file. This should be incremented any
- time the data in the domain is changed. When a secondary wants to check if
- its data is up-to-date, it checks the serial number on the primary's SOA
- record.
-
- * *Refresh* -- A time, in seconds, specifying how often the secondary should
- check the serial number on the primary, and start a new transfer if the
- primary has newer data.
-
- * *Retry* -- If a secondary fails to connect to the primary when the refresh
- time has elapsed (for example, if the host is down), this value specifies, in
- seconds, how often the connection should be retried.
-
- * *Expire* -- If the retries fail to reach the primary within this number of
- seconds, the secondary destroys its copies of the zone data file(s), and
- stops answering requests for the domain. This stops very old and potentially
- inaccurate data from remaining in circulation.
-
- * *TTL* -- This field specifies a time, in seconds, that the resource records
- in this zone should remain valid in the caches of other nameservers. If the
- data is volatile, this value should be short. TTL is a commonly-used acronym,
- that stands for "Time To Live".
-
-### Name Resolution
-
-DNS clients are configured with the addresses of DNS servers. Usually, these are
-servers which are authoritative for the domain of which they are a member. All
-requests for name resolution start with a request to one of these local servers.
-DNS queries can be of two forms:
-
- * A *recursive* query asks the nameserver to resolve a name completely, and
- return the result. If the request cannot be satisfied directly, the
- nameserver looks in its configuration and caches for a server higher up the
- domain tree which may have more information. In the worst case, this will be
- a list of pre-configured servers for the root domain. These addresses are
- returned in a response called a *referral*. The local nameserver must then
- send its request to one of these servers.
-
- * Normally, this will be an *iterative* query, which asks the second nameserver
- to either respond with an authoritative reply, or with the addresses of
- nameservers (NS records) listed in its tables or caches as authoritative for
- the relevant zone. The local nameserver then makes iterative queries, walking
- the tree downwards until an authoritative answer is found (either positive or
- negative) and returned to the client.
-
-In some configurations, such as when firewalls prevent direct IP communications
-between DNS clients and external nameservers, or when a site is connected to the
-rest of the world via a slow link, a nameserver can be configured with
-information about a *forwarder*. This is an external nameserver to which the
-local nameserver should make requests as a client would, asking the external
-nameserver to perform the full recursive name lookup, and return the result in a
-single query (which can then be cached), rather than reply with referrals.
-
-### Reverse Resolution
-
-The DNS provides resolution from a textual name to a resource record, such as an
-A record with an IP address. It does not provide a means, other than exhaustive
-search, to match in the opposite direction; there is no mechanism to ask which
-name is bound to a particular RR.
-
-For many RR types, this is of no real consequence, however it is often useful to
-identify by name the host which owns a particular IP address. Rather than
-complicate the design and implementation of the DNS database engine by providing
-matching functions in both directions, the DNS utilises the existing mechanisms
-and creates a special namespace, populated with PTR records, for IP address to
-name resolution. Resolving in this manner is often called *reverse resolution*,
-despite the inaccurate implications of the term.
-
-The manner in which this is achieved is as follows:
-
- * A normal domain name is reserved and defined to be for the purpose of mapping
- IP addresses. The domain name used is `in-addr.arpa.` which shows the
- historical origins of the Internet in the US Government's Defence Advanced
- Research Projects Agency's funding program.
-
- * This domain is then subdivided and delegated according to the structure of IP
- addresses. IP addresses are often written in *decimal dotted quad notation*,
- where each octet of the 4-octet long address is written in decimal, separated
- by dots. IP address ranges are usually delegated with more and more of the
- left-most parts of the address in common as the delegation gets smaller.
- Thus, to allow delegation of the reverse lookup domain to be done easily,
- this is turned around when used with the hierarchical DNS namespace, which
- places higher level domains on the right of the name.
-
- * Each byte of the IP address is written, as an ASCII text representation of
- the number expressed in decimal, with the octets in reverse order, separated
- by dots and appended with the in-addr.arpa. domain name. For example, to
- determine the hostname of a network device with IP address 11.22.33.44, this
- algorithm would produce the string `44.33.22.11.in-addr.arpa.` which is a
- legal, structured Domain Name. A normal nameservice query would then be sent
- to the nameserver asking for a PTR record bound to the generated name.
-
- * The PTR record, if found, will contain the FQDN of a host.
-
-One consequence of this is that it is possible for mismatch to occur. Resolving
-a name into an A record, and then resolving the name built from the address in
-that A record to a PTR record, may not result in a PTR record which contains the
-original name. There is no restriction within the DNS that the "reverse" mapping
-must coincide with the "forward" mapping. This is a useful feature in some
-circumstances, particularly when it is required that more than one name has an A
-record bound to it which contains the same IP address.
-
-While there is no such restriction within the DNS, some application server
-programs or network libraries will reject connections from hosts that do not
-satisfy the following test:
-
- * the state information included with an incoming connection includes the IP
- address of the source of the request.
-
- * a PTR lookup is done to obtain an FQDN of the host making the connection
-
- * an A lookup is then done on the returned name, and the connection rejected if
- the source IP address is not listed amongst the A records that get returned.
-
-This is done as a security precaution, to help detect and prevent malicious
-sites impersonating other sites by configuring their own PTR records to return
-the names of hosts belonging to another organisation.
-
-## The DNS Files
-
-Now let's look at actually setting up a small DNS enabled network. We will
-continue to use the examples mentioned in [Chapter 24, *Setting up TCP/IP on
-NetBSD in practice*](chap-net-practice.html "Chapter 24. Setting up TCP/IP on
-NetBSD in practice"), i.e. we assume that:
-
- * Our IP networking is working correctly
- * We have IPNAT working correctly
- * Currently all hosts use the ISP for DNS
-
-Our Name Server will be the `strider` host which also runs IPNAT, and our two
-clients use "strider" as a gateway. It is not really relevant as to what type of
-interface is on "strider", but for argument's sake we will say a 56k dial up
-connection.
-
-So, before going any further, let's look at our `/etc/hosts` file on "strider"
-before we have made the alterations to use DNS.
-
-**Example strider's `/etc/hosts` file**
-
- 127.0.0.1 localhost
- 192.168.1.1 strider
- 192.168.1.2 samwise sam
- 192.168.1.3 wormtongue worm
-
-This is not exactly a huge network, but it is worth noting that the same rules
-apply for larger networks as we discuss in the context of this section.
-
-The other assumption we want to make is that the domain we want to set up is
-`diverge.org`, and that the domain is only known on our internal network, and
-not worldwide. Proper registration of the nameserver's IP address as primary
-would be needed in addition to a static IP. These are mostly administrative
-issues which are left out here.
-
-The NetBSD operating system provides a set of config files for you to use for
-setting up DNS. Along with a default `/etc/named.conf`, the following files are
-stored in the `/etc/namedb` directory:
-
- * `localhost`
- * `127`
- * `loopback.v6`
- * `root.cache`
-
-You will see modified versions of these files in this section, and I strongly
-suggest making a backup copy of the original files for reference purposes.
-
-*Note*: The examples in this chapter refer to BIND major version 8, however, it
-should be noted that format of the name database and other config files are
-almost 100% compatible between version. The only difference I noticed was that
-the `$TTL` information was not required.
-
-### /etc/named.conf
-
-The first file we want to look at is `/etc/named.conf`. This file is the config
-file for bind (hence the catchy name). Setting up system like the one we are
-doing is relatively simple. First, here is what mine looks like:
-
- options {
- directory "/etc/namedb";
- allow-transfer { 192.168.1.0/24; };
- allow-query { 192.168.1.0/24; };
- listen-on port 53 { 192.168.1.1; };
- };
-
- zone "localhost" {
- type master;
- notify no;
- file "localhost";
- };
-
- zone "127.IN-ADDR.ARPA" {
- type master;
- notify no;
- file "127";
- };
-
- zone "0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.int" {
- type master;
- file "loopback.v6";
- };
-
- zone "diverge.org" {
- type master;
- notify no;
- file "diverge.org";
- };
-
- zone "1.168.192.in-addr.arpa" {
- type master;
- notify no;
- file "1.168.192";
- };
-
- zone "." in {
- type hint;
- file "root.cache";
- };
-
-Note that in my `named.conf` the root (".") section is last, that is because
-there is another domain called diverge.org on the internet (I happen to own it)
-so I want the resolver to look out on the internet last. This is not normally
-the case on most systems.
-
-Another very important thing to remember here is that if you have an internal
-setup, in other words no live internet connection and/or no need to do root
-server lookups, comment out the root (".") zone. It may cause lookup problems if
-a particular client decides it wants to reference a domain on the internet,
-which our server couldn't resolve itself.
-
-Looks like a pretty big mess, upon closer examination it is revealed that many
-of the lines in each section are somewhat redundant. So we should only have to
-explain them a few times.
-
-Lets go through the sections of `named.conf`:
-
-#### options
-
-This section defines some global parameters, most noticeable is the location of
-the DNS tables, on this particular system, they will be put in `/etc/namedb` as
-indicated by the "directory" option.
-
-Following are the rest of the params:
-
- * `allow-transfer` -- This option lists which remote DNS servers acting as
- secondaries are allowed to do zone transfers, i.e. are allowed to read all
- DNS data at once. For privacy reasons, this should be restricted to secondary
- DNS servers only.
-
- * `allow-query` -- This option defines hosts from what network may query this
- name server at all. Restricting queries only to the local network
- (192.168.1.0/24) prevents queries arriving on the DNS server's external
- interface, and prevent possible privacy issues.
-
- * `listen-on port` -- This option defined the port and associated IP addresses
- this server will run
- [[!template id=man name="named" section="8"]]
- on. Again, the "external" interface is not listened here, to prevent queries
- getting received from "outside".
-
-The rest of the `named.conf` file consists of `zone`s. A zone is an area that
-can have items to resolve attached, e.g. a domain can have hostnames attached to
-resolve into IP addresses, and a reverse-zone can have IP addresses attached
-that get resolved back into hostnames. Each zone has a file associated with it,
-and a table within that file for resolving that particular zone. As is readily
-apparent, their format in `named.conf` is strikingly similar, so I will
-highlight just one of their records:
-
-#### zone diverge.org
-
- * `type` -- The type of a zone is usually of type "master" in all cases except
- for the root zone `.` and for zones that a secondary (backup) service is
- provided - the type obviously is "secondary" in the latter case.
-
- * `notify` -- Do you want to send out notifications to secondaries when your
- zone changes? Obviously not in this setup, so this is set to "no".
-
- * `file` -- This option sets the filename in our `/etc/namedb` directory where
- records about this particular zone may be found. For the "diverge.org" zone,
- the file `/etc/namedb/diverge.org` is used.
-
-### /etc/namedb/localhost
-
-For the most part, the zone files look quite similar, however, each one does
-have some unique properties. Here is what the `localhost` file looks like:
-
- 1|$TTL 3600
- 2|@ IN SOA strider.diverge.org. root.diverge.org. (
- 3| 1 ; Serial
- 4| 8H ; Refresh
- 5| 2H ; Retry
- 6| 1W ; Expire
- 7| 1D) ; Minimum TTL
- 8| IN NS localhost.
- 9|localhost. IN A 127.0.0.1
- 10| IN AAAA ::1
-
-Line by line:
-
- * *Line 1*: This is the Time To Live for lookups, which defines how long other
- DNS servers will cache that value before discarding it. This value is
- generally the same in all the files.
-
- * *Line 2*: This line is generally the same in all zone files except
- `root.cache`. It defines a so-called "Start Of Authority" (SOA) header, which
- contains some basic information about a zone. Of specific interest on this
- line are "strider.diverge.org." and "root.diverge.org." (note the trailing
- dots!). Obviously one is the name of this server and the other is the contact
- for this DNS server, in most cases root seems a little ambiguous, it is
- preferred that a regular email account be used for the contact information,
- with the "@" replaced by a "." (for example, mine would be
- "jrf.diverge.org.").
-
- * *Line 3*: This line is the serial number identifying the "version" of the
- zone's data set (file). The serial number should be incremented each time
- there is a change to the file, the usual format is to either start with a
- value of "1" and increase it for every change, or use a value of "YYYYMMDDNN"
- to encode year (YYYY), month (MM), day (DD) and change within one day (NN) in
- the serial number.
-
- * *Line 4*: This is the refresh rate of the server, in this file it is set to
- once every 8 hours.
-
- * *Line 5*: The retry rate.
-
- * *Line 6*: Lookup expiry.
-
- * *Line 7*: The minimum Time To Live.
-
- * *Line 8*: This is the Nameserver line, which uses a "NS" resource record to
- show that "localhost" is the only DNS server handing out data for this zone
- (which is "@", which indicates the zone name used in the `named.conf` file,
- i.e. "diverge.org") is, well, "localhost".
-
- * *Line 9*: This is the localhost entry, which uses an "A" resource record to
- indicate that the name "localhost" should be resolved into the IP-address
- 127.0.0.1 for IPv4 queries (which specifically ask for the "A" record).
-
- * *Line 10*: This line is the IPv6 entry, which returns ::1 when someone asks
- for an IPv6-address (by specifically asking for the AAAA record) of
- "localhost.".
-
-### /etc/namedb/zone.127.0.0
-
-This is the reverse lookup file (or zone) to resolve the special IP address
-127.0.0.1 back to "localhost":
-
- 1| $TTL 3600
- 2| @ IN SOA strider.diverge.org. root.diverge.org. (
- 3| 1 ; Serial
- 4| 8H ; Refresh
- 5| 2H ; Retry
- 6| 1W ; Expire
- 7| 1D) ; Minimum TTL
- 8| IN NS localhost.
- 9| 1.0.0 IN PTR localhost.
-
-In this file, all of the lines are the same as the localhost zonefile with
-exception of line 9, this is the reverse lookup (PTR) record. The zone used here
-is "@" again, which got set to the value given in `named.conf`, i.e.
-"127.in-addr.arpa". This is a special "domain" which is used to do
-reverse-lookup of IP addresses back into hostnames. For it to work, the four
-bytes of the IPv4 address are reserved, and the domain "in-addr.arpa" attached,
-so to resolve the IP address "127.0.0.1", the PTR record of
-"1.0.0.127.in-addr.arpa" is queried, which is what is defined in that line.
-
-### /etc/namedb/diverge.org
-
-This zone file is populated by records for all of our hosts. Here is what it
-looks like:
-
- 1| $TTL 3600
- 2| @ IN SOA strider.diverge.org. root.diverge.org. (
- 3| 1 ; serial
- 4| 8H ; refresh
- 5| 2H ; retry
- 6| 1W ; expire
- 7| 1D ) ; minimum seconds
- 8| IN NS strider.diverge.org.
- 9| IN MX 10 strider.diverge.org. ; primary mail server
- 10| IN MX 20 samwise.diverge.org. ; secondary mail server
- 11| strider IN A 192.168.1.1
- 12| samwise IN A 192.168.1.2
- 13| www IN CNAME samwise.diverge.org.
- 14| worm IN A 192.168.1.3
-
-There is a lot of new stuff here, so lets just look over each line that is new
-here:
-
- * *Line 9*: This line shows our mail exchanger (MX), in this case it is
- "strider". The number that precedes "strider.diverge.org." is the priority
- number, the lower the number their higher the priority. The way we are setup
- here is if "strider" cannot handle the mail, then "samwise" will.
-
- * *Line 11*: CNAME stands for canonical name, or an alias for an existing
- hostname, which must have an A record. So we have aliased `www.diverge.org`
- to `samwise.diverge.org`.
-
-The rest of the records are simply mappings of IP address to a full name (A
-records).
-
-### /etc/namedb/1.168.192
-
-This zone file is the reverse file for all of the host records, to map their IP
-numbers we use on our private network back into hostnames. The format is similar
-to that of the "localhost" version with the obvious exception being the
-addresses are different via the different zone given in the `named.conf` file,
-i.e. "0.168.192.in-addr.arpa" here:
-
- 1|$TTL 3600
- 2|@ IN SOA strider.diverge.org. root.diverge.org. (
- 3| 1 ; serial
- 4| 8H ; refresh
- 5| 2H ; retry
- 6| 1W ; expire
- 7| 1D ) ; minimum seconds
- 8| IN NS strider.diverge.org.
- 9|1 IN PTR strider.diverge.org.
- 10|2 IN PTR samwise.diverge.org.
- 11|3 IN PTR worm.diverge.org.
-
-### /etc/namedb/root.cache
-
-This file contains a list of root name servers for your server to query when it
-gets requests outside of its own domain that it cannot answer itself. Here are
-first few lines of a root zone file:
-
- ;
- ; This file holds the information on root name servers needed to
- ; initialize cache of Internet domain name servers
- ; (e.g. reference this file in the "cache . "
- ; configuration file of BIND domain name servers).
- ;
- ; This file is made available by InterNIC
- ; under anonymous FTP as
- ; file /domain/db.cache
- ; on server FTP.INTERNIC.NET
- ; -OR- RS.INTERNIC.NET
- ;
- ; last update: Jan 29, 2004
- ; related version of root zone: 2004012900
- ;
- ;
- ; formerly NS.INTERNIC.NET
- ;
- . 3600000 IN NS A.ROOT-SERVERS.NET.
- A.ROOT-SERVERS.NET. 3600000 A 198.41.0.4
- ;
- ; formerly NS1.ISI.EDU
- ;
- . 3600000 NS B.ROOT-SERVERS.NET.
- B.ROOT-SERVERS.NET. 3600000 A 192.228.79.201
- ;
- ; formerly C.PSI.NET
- ;
- . 3600000 NS C.ROOT-SERVERS.NET.
- C.ROOT-SERVERS.NET. 3600000 A 192.33.4.12
- ;
- ...
-
-This file can be obtained from ISC at and usually comes
-with a distribution of BIND. A `root.cache` file is included in the NetBSD
-operating system's "etc" set.
-
-This section has described the most important files and settings for a DNS
-server. Please see the BIND documentation in `/usr/src/dist/bind/doc/bog` and
-[[!template id=man name="named.conf" section="5"]]
-for more information.
-
-## Using DNS
-
-In this section we will look at how to get DNS going and setup "strider" to use
-its own DNS services.
-
-Setting up named to start automatically is quite simple. In `/etc/rc.conf`
-simply set `named=yes`. Additional options can be specified in `named_flags`,
-for example, I like to use `-g nogroup -u nobody`, so a non-root account runs
-the "named" process.
-
-In addition to being able to startup "named" at boot time, it can also be
-controlled with the `ndc` command. In a nutshell the `ndc` command can stop,
-start or restart the named server process. It can also do a great many other
-things. Before use, it has to be setup to communicate with the "named" process,
-see the [[!template id=man name="ndc" section="8"]]
-and
-[[!template id=man name="named.conf" section="5"]]
-man pages for more details on setting up communication channels between "ndc"
-and the "named" process.
-
-Next we want to point "strider" to itself for lookups. We have two simple steps,
-first, decide on our resolution order. On a network this small, it is likely
-that each host has a copy of the hosts table, so we can get away with using
-`/etc/hosts` first, and then DNS. However, on larger networks it is much easier
-to use DNS. Either way, the file where order of name services used for
-resolution is determined is `/etc/nsswitch.conf` (see
-[[`nsswitch.conf`|guide/net-practice#ex-nsswitch]]. Here is part of a typical
-`nsswitch.conf`:
-
- ...
- group_compat: nis
- hosts: files dns
- netgroup: files [notfound=return] nis
- ...
-
-The line we are interested in is the "hosts" line. "files" means the system uses
-the `/etc/hosts` file first to determine ip to name translation, and if it can't
-find an entry, it will try DNS.
-
-The next file to look at is `/etc/resolv.conf`, which is used to configure DNS
-lookups ("resolution") on the client side. The format is pretty self explanatory
-but we will go over it anyway:
-
- domain diverge.org
- search diverge.org
- nameserver 192.168.1.1
-
-In a nutshell this file is telling the resolver that this machine belongs to the
-"diverge.org" domain, which means that lookups that contain only a hostname
-without a "." gets this domain appended to build a FQDN. If that lookup doesn't
-succeed, the domains in the "search" line are tried next. Finally, the
-"nameserver" line gives the IP addresses of one or more DNS servers that should
-be used to resolve DNS queries.
-
-To test our nameserver we can use several commands, for example:
-
- # host sam
- sam.diverge.org has address 192.168.1.2
-
-As can be seen, the domain was appended automatically here, using the value from
-`/etc/resolv.conf`. Here is another example, the output of running
-`host www.yahoo.com`:
-
- $ host www.yahoo.com
- www.yahoo.com is an alias for www.yahoo.akadns.net.
- www.yahoo.akadns.net has address 68.142.226.38
- www.yahoo.akadns.net has address 68.142.226.39
- www.yahoo.akadns.net has address 68.142.226.46
- www.yahoo.akadns.net has address 68.142.226.50
- www.yahoo.akadns.net has address 68.142.226.51
- www.yahoo.akadns.net has address 68.142.226.54
- www.yahoo.akadns.net has address 68.142.226.55
- www.yahoo.akadns.net has address 68.142.226.32
-
-Other commands for debugging DNS besides
-[[!template id=man name="host" section="1"]] are
-[[!template id=man name="nslookup" section="8"]]
-and
-[[!template id=man name="dig" section="1"]]. Note
-that
-[[!template id=man name="ping" section="8"]]
-is *not* useful for debugging DNS, as it will use whatever is configured in
-`/etc/nsswitch.conf` to do the name-lookup.
-
-At this point the server is configured properly. The procedure for setting up
-the client hosts are easier, you only need to setup `/etc/nsswitch.conf` and
-`/etc/resolv.conf` to the same values as on the server.
-
-## Setting up a caching only name server
-
-A caching only name server has no local zones; all the queries it receives are
-forwarded to the root servers and the replies are accumulated in the local
-cache. The next time the query is performed the answer will be faster because
-the data is already in the server's cache. Since this type of server doesn't
-handle local zones, to resolve the names of the local hosts it will still be
-necessary to use the already known `/etc/hosts` file.
-
-Since NetBSD supplies defaults for all the files needed by a caching only
-server, it only needs to be enabled and started and is immediately ready for
-use! To enable named, put `named=yes` into `/etc/rc.conf`, and tell the system
-to use it adding the following line to the `/etc/resolv.conf` file:
-
- # cat /etc/resolv.conf
- nameserver 127.0.0.1
-
-Now we can start named:
-
- # sh /etc/rc.d/named restart
-
-### Testing the server
-
-Now that the server is running we can test it using the
-[[!template id=man name="nslookup" section="8"]]
-program:
-
- $ nslookup
- Default server: localhost
- Address: 127.0.0.1
-
- >
-
-Let's try to resolve a host name, for example "www.NetBSD.org":
-
- > www.NetBSD.org
- Server: localhost
- Address: 127.0.0.1
-
- Name: www.NetBSD.org
- Address: 204.152.190.12
-
-If you repeat the query a second time, the result is slightly different:
-
- > www.NetBSD.org
- Server: localhost
- Address: 127.0.0.1
-
- Non-authoritative answer:
- Name: www.NetBSD.org
- Address: 204.152.190.12
-
-As you've probably noticed, the address is the same, but the message
-`Non-authoritative answer` has appeared. This message indicates that the answer
-is not coming from an authoritative server for the domain NetBSD.org but from
-the cache of our own server.
-
-The results of this first test confirm that the server is working correctly.
-
-We can also try the
-[[!template id=man name="host" section="1"]] and
-[[!template id=man name="dig" section="1"]] commands,
-which give the following result.
-
- $ host www.NetBSD.org
- www.NetBSD.org has address 204.152.190.12
- $
- $ dig www.NetBSD.org
-
- ; <<>> DiG 8.3 <<>> www.NetBSD.org
- ;; res options: init recurs defnam dnsrch
- ;; got answer:
- ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19409
- ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 0
- ;; QUERY SECTION:
- ;; www.NetBSD.org, type = A, class = IN
-
- ;; ANSWER SECTION:
- www.NetBSD.org. 23h32m54s IN A 204.152.190.12
-
- ;; AUTHORITY SECTION:
- NetBSD.org. 23h32m54s IN NS uucp-gw-1.pa.dec.com.
- NetBSD.org. 23h32m54s IN NS uucp-gw-2.pa.dec.com.
- NetBSD.org. 23h32m54s IN NS ns.NetBSD.org.
- NetBSD.org. 23h32m54s IN NS adns1.berkeley.edu.
- NetBSD.org. 23h32m54s IN NS adns2.berkeley.edu.
-
- ;; Total query time: 14 msec
- ;; FROM: miyu to SERVER: 127.0.0.1
- ;; WHEN: Thu Nov 25 22:59:36 2004
- ;; MSG SIZE sent: 32 rcvd: 175
-
-As you can see
-[[!template id=man name="dig" section="1"]] gives
-quite a bit of output, the expected answer can be found in the "ANSWER SECTION".
-The other data given may be of interest when debugging DNS problems.
-
+This page was moved to:
+[The NetBSD Guide - The Domain Name System](//www.NetBSD.org/docs/guide/en/chap-dns.html)