29.6 域名系统 (DNS)

29.6.6.1 /etc/namedb/named.conf

// $FreeBSD$
//
// Refer to the named.conf(5) and named(8) man pages, and the documentation
// in /usr/share/doc/bind9 for more details.
//
// If you are going to set up an authoritative server, make sure you
// understand the hairy details of how DNS works.  Even with
// simple mistakes, you can break connectivity for affected parties,
// or cause huge amounts of useless Internet traffic.

options {
    // Relative to the chroot directory, if any
    directory   "/etc/namedb";
    pid-file    "/var/run/named/pid";
    dump-file   "/var/dump/named_dump.db";
    statistics-file "/var/stats/named.stats";

// If named is being used only as a local resolver, this is a safe default.
// For named to be accessible to the network, comment this option, specify
// the proper IP address, or delete this option.
    listen-on   { 127.0.0.1; };

// If you have IPv6 enabled on this system, uncomment this option for
// use as a local resolver.  To give access to the network, specify
// an IPv6 address, or the keyword "any".
//  listen-on-v6    { ::1; };

// These zones are already covered by the empty zones listed below.
// If you remove the related empty zones below, comment these lines out.
    disable-empty-zone "255.255.255.255.IN-ADDR.ARPA";
    disable-empty-zone "0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA";
    disable-empty-zone "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA";

// If you've got a DNS server around at your upstream provider, enter
// its IP address here, and enable the line below.  This will make you
// benefit from its cache, thus reduce overall DNS traffic in the Internet.
/*
    forwarders {
        127.0.0.1;
    };
*/

// If the 'forwarders' clause is not empty the default is to 'forward first'
// which will fall back to sending a query from your local server if the name
// servers in 'forwarders' do not have the answer.  Alternatively you can
// force your name server to never initiate queries of its own by enabling the
// following line:
//  forward only;

// If you wish to have forwarding configured automatically based on
// the entries in /etc/resolv.conf, uncomment the following line and
// set named_auto_forward=yes in /etc/rc.conf.  You can also enable
// named_auto_forward_only (the effect of which is described above).
//  include "/etc/namedb/auto_forward.conf";

　　正如注释所言， 如果希望从上级缓存中受益， 可以在此处启用 forwarders。 正常情况下， 域名服务器会逐级地查询 Internet 来找到特定的域名服务器， 直到得到答案为止。 这个选项将让它首先查询上级域名服务器 (或另外提供的域名服务器)， 从而从它们的缓存中得到结果。 如果上级域名服务器是一个繁忙的高速域名服务器， 则启用它将有助于改善服务品质。

   /*
       Modern versions of BIND use a random UDP port for each outgoing
       query by default in order to dramatically reduce the possibility
       of cache poisoning.  All users are strongly encouraged to utilize
       this feature, and to configure their firewalls to accommodate it.

       AS A LAST RESORT in order to get around a restrictive firewall
       policy you can try enabling the option below.  Use of this option
       will significantly reduce your ability to withstand cache poisoning
       attacks, and should be avoided if at all possible.

       Replace NNNNN in the example with a number between 49160 and 65530.
    */
    // query-source address * port NNNNN;
};

// If you enable a local name server, don't forget to enter 127.0.0.1
// first in your /etc/resolv.conf so this server will be queried.
// Also, make sure to enable it in /etc/rc.conf.

// The traditional root hints mechanism. Use this, OR the slave zones below.
zone "." { type hint; file "named.root"; };

/*  Slaving the following zones from the root name servers has some
    significant advantages:
    1. Faster local resolution for your users
    2. No spurious traffic will be sent from your network to the roots
    3. Greater resilience to any potential root server failure/DDoS

    On the other hand, this method requires more monitoring than the
    hints file to be sure that an unexpected failure mode has not
    incapacitated your server.  Name servers that are serving a lot
    of clients will benefit more from this approach than individual
    hosts.  Use with caution.

    To use this mechanism, uncomment the entries below, and comment
    the hint zone above.
*/
/*
zone "." {
    type slave;
    file "slave/root.slave";
    masters {
        192.5.5.241;    // F.ROOT-SERVERS.NET.
    };
    notify no;
};
zone "arpa" {
    type slave;
    file "slave/arpa.slave";
    masters {
        192.5.5.241;    // F.ROOT-SERVERS.NET.
    };
    notify no;
};
zone "in-addr.arpa" {
    type slave;
    file "slave/in-addr.arpa.slave";
    masters {
        192.5.5.241;    // F.ROOT-SERVERS.NET.
    };
    notify no;
};
*/

/*  Serving the following zones locally will prevent any queries
    for these zones leaving your network and going to the root
    name servers.  This has two significant advantages:
    1. Faster local resolution for your users
    2. No spurious traffic will be sent from your network to the roots
*/
// RFC 1912
zone "localhost"    { type master; file "master/localhost-forward.db"; };
zone "127.in-addr.arpa" { type master; file "master/localhost-reverse.db"; };
zone "255.in-addr.arpa" { type master; file "master/empty.db"; };

// RFC 1912-style zone for IPv6 localhost address
zone "0.ip6.arpa"   { type master; file "master/localhost-reverse.db"; };

// "This" Network (RFCs 1912 and 3330)
zone "0.in-addr.arpa"       { type master; file "master/empty.db"; };

// Private Use Networks (RFC 1918)
zone "10.in-addr.arpa"      { type master; file "master/empty.db"; };
zone "16.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "17.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "18.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "19.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "20.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "21.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "22.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "23.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "24.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "25.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "26.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "27.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "28.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "29.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "30.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "31.172.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "168.192.in-addr.arpa" { type master; file "master/empty.db"; };

// Link-local/APIPA (RFCs 3330 and 3927)
zone "254.169.in-addr.arpa" { type master; file "master/empty.db"; };

// TEST-NET for Documentation (RFC 3330)
zone "2.0.192.in-addr.arpa" { type master; file "master/empty.db"; };

// Router Benchmark Testing (RFC 3330)
zone "18.198.in-addr.arpa"  { type master; file "master/empty.db"; };
zone "19.198.in-addr.arpa"  { type master; file "master/empty.db"; };

// IANA Reserved - Old Class E Space
zone "240.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "241.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "242.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "243.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "244.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "245.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "246.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "247.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "248.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "249.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "250.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "251.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "252.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "253.in-addr.arpa"     { type master; file "master/empty.db"; };
zone "254.in-addr.arpa"     { type master; file "master/empty.db"; };

// IPv6 Unassigned Addresses (RFC 4291)
zone "1.ip6.arpa"       { type master; file "master/empty.db"; };
zone "3.ip6.arpa"       { type master; file "master/empty.db"; };
zone "4.ip6.arpa"       { type master; file "master/empty.db"; };
zone "5.ip6.arpa"       { type master; file "master/empty.db"; };
zone "6.ip6.arpa"       { type master; file "master/empty.db"; };
zone "7.ip6.arpa"       { type master; file "master/empty.db"; };
zone "8.ip6.arpa"       { type master; file "master/empty.db"; };
zone "9.ip6.arpa"       { type master; file "master/empty.db"; };
zone "a.ip6.arpa"       { type master; file "master/empty.db"; };
zone "b.ip6.arpa"       { type master; file "master/empty.db"; };
zone "c.ip6.arpa"       { type master; file "master/empty.db"; };
zone "d.ip6.arpa"       { type master; file "master/empty.db"; };
zone "e.ip6.arpa"       { type master; file "master/empty.db"; };
zone "0.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "1.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "2.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "3.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "4.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "5.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "6.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "7.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "8.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "9.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "a.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "b.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "0.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "1.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "2.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "3.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "4.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "5.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "6.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "7.e.f.ip6.arpa"       { type master; file "master/empty.db"; };

// IPv6 ULA (RFC 4193)
zone "c.f.ip6.arpa"     { type master; file "master/empty.db"; };
zone "d.f.ip6.arpa"     { type master; file "master/empty.db"; };

// IPv6 Link Local (RFC 4291)
zone "8.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "9.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "a.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "b.e.f.ip6.arpa"       { type master; file "master/empty.db"; };

// IPv6 Deprecated Site-Local Addresses (RFC 3879)
zone "c.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "d.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "e.e.f.ip6.arpa"       { type master; file "master/empty.db"; };
zone "f.e.f.ip6.arpa"       { type master; file "master/empty.db"; };

// IP6.INT is Deprecated (RFC 4159)
zone "ip6.int"          { type master; file "master/empty.db"; };

// NB: Do not use the IP addresses below, they are faked, and only
// serve demonstration/documentation purposes!
//
// Example slave zone config entries.  It can be convenient to become
// a slave at least for the zone your own domain is in.  Ask
// your network administrator for the IP address of the responsible
// master name server.
//
// Do not forget to include the reverse lookup zone!
// This is named after the first bytes of the IP address, in reverse
// order, with ".IN-ADDR.ARPA" appended, or ".IP6.ARPA" for IPv6.
//
// Before starting to set up a master zone, make sure you fully
// understand how DNS and BIND work.  There are sometimes
// non-obvious pitfalls.  Setting up a slave zone is usually simpler.
//
// NB: Don't blindly enable the examples below. :-)  Use actual names
// and addresses instead.

/* An example dynamic zone
key "exampleorgkey" {
    algorithm hmac-md5;
    secret "sf87HJqjkqh8ac87a02lla==";
};
zone "example.org" {
    type master;
    allow-update {
        key "exampleorgkey";
    };
    file "dynamic/example.org";
};
*/

/* Example of a slave reverse zone
zone "1.168.192.in-addr.arpa" {
    type slave;
    file "slave/1.168.192.in-addr.arpa";
    masters {
        192.168.1.1;
    };
};
*/

　　在 named.conf 中， 还给出了从域、转发域和反解析域的例子。

　　如果新增了域， 就必需在 named.conf 中加入对应的项目。

　　例如， 用于 example.org 的域文件的描述类似下面这样：

zone "example.org" {
    type master;
    file "master/example.org";
};

　　如 type 语句所标示的那样， 这是一个主域， 其信息保存在 /etc/namedb/master/example.org 中， 如 file 语句所示。

zone "example.org" {
    type slave;
    file "slave/example.org";
};

　　在从域的情形中， 所指定的域的信息会从主域名服务器传递过来， 并保存到对应的文件中。 当主域服务器发生问题或不可达时， 从域名服务器就有一份可用的域名信息， 从而能够对外提供服务。

29.6.6.2 域文件

　　下面的例子展示了用于 example.org 的主域文件 (存放于 /etc/namedb/master/example.org)：

$TTL 3600        ; 1 hour default TTL
example.org.    IN      SOA      ns1.example.org. admin.example.org. (
                                2006051501      ; Serial
                                10800           ; Refresh
                                3600            ; Retry
                                604800          ; Expire
                                300             ; Negative Reponse TTL
                        )

; DNS Servers
                IN      NS      ns1.example.org.
                IN      NS      ns2.example.org.

; MX Records
                IN      MX 10   mx.example.org.
                IN      MX 20   mail.example.org.

                IN      A       192.168.1.1

; Machine Names
localhost       IN      A       127.0.0.1
ns1             IN      A       192.168.1.2
ns2             IN      A       192.168.1.3
mx              IN      A       192.168.1.4
mail            IN      A       192.168.1.5

; Aliases
www             IN      CNAME   example.org.

　　请注意以 “.” 结尾的主机名是全称主机名， 而结尾没有 “.” 的则是相对于原点的主机名。 例如， ns1 将被转换为 ns1.example.org.

　　域信息文件的格式如下：

记录名          IN 记录类型     值

　　最常用的 DNS 记录：

example.org. IN SOA ns1.example.org. admin.example.org. (
                        2006051501      ; Serial
                        10800           ; Refresh after 3 hours
                        3600            ; Retry after 1 hour
                        604800          ; Expire after 1 week
                        300 )           ; Negative Reponse TTL

       IN NS           ns1.example.org.

　　这是一个 NS 项。 每个准备提供权威应答的服务器都必须有一个对应项。

localhost       IN      A       127.0.0.1
ns1             IN      A       192.168.1.2
ns2             IN      A       192.168.1.3
mx              IN      A       192.168.1.4
mail            IN      A       192.168.1.5

　　A 记录指明了机器名。 正如在前面所看到的， ns1.example.org 将解析为 192.168.1.2。

                IN      A       192.168.1.1

　　这一行把当前原点 example.org 指定为使用 IP 地址 192.168.1.1。

www             IN CNAME        @

　　正规名 (CNAME) 记录通常用于为某台机器指定别名。 在这个例子中， 将 www 指定成了 “主” 机器的一个别名， 后者的名字与域名 example.org (192.168.1.1) 相同。 CNAME 不能同与之有相同名字的任何其它记录并存。

               IN MX   10      mail.example.org.

　　MX 记录表示哪个邮件服务器负责接收发到这个域的邮件。 mail.example.org 是邮件服务器的主机名， 而 10 则是它的优先级。

　　可以有多台邮件服务器， 其优先级分别是 10、 20 等等。 尝试向 example.org 投递邮件的服务器， 会首先尝试优先级最高的 MX (优先级数值最小的记录)、 接着尝试次高的， 并重复这一过程直到邮件递达为止。

　　in-addr.arpa 域名信息文件 (反向 DNS)， 采用的格式是同样的， 只是 PTR 项代替了 A 或 CNAME 的位置。

$TTL 3600

1.168.192.in-addr.arpa. IN SOA ns1.example.org. admin.example.org. (
                        2006051501      ; Serial
                        10800           ; Refresh
                        3600            ; Retry
                        604800          ; Expire
                        300 )           ; Negative Reponse TTL

        IN      NS      ns1.example.org.
        IN      NS      ns2.example.org.

1       IN      PTR     example.org.
2       IN      PTR     ns1.example.org.
3       IN      PTR     ns2.example.org.
4       IN      PTR     mx.example.org.
5       IN      PTR     mail.example.org.

　　这个文件给出了上述假想域中 IP 地址到域名的映射关系。

　　需要说明的是， 在 PTR 记录右侧的名字必须是全称域名 (也就是必须以 “.” 结束)。