什么是辅助DNS

辅助DNS服务器是一种容错设计，考虑的是一旦DNS主服务器出现故障或因负载太重无法及时响应客户机请求，辅助服务器将挺身而出为主服务器排忧解难。DNS的原始解析记录在主DNS服务器上进行设置，辅助服务器的区域数据都是从主服务器复制而来，因此辅助服务器的数据都是只读的。

测试环境

服务器系统：Redhat Linux 5 +Bind 9.3.6

主DNS服务器：192.168.0.200

辅助DSN服务器：192.168.0.201

测试正向域：liusuping.com

测试反向域：192.168.0.0

配置步骤

首先配置主DNS服务器，具体步骤参见[Redhat Linux DNS服务软件bind的安装及配置]

建立一个解析域liusuping.com

[root@a named]# cat /etc/named.rfc1912.zones
zone "liusuping.com" IN {
        type master;
        file "liusuping.com.zone";
        allow-update { none; };
};

zone "0.168.192.in-addr.arpa" IN {
        type master;
        file "liusuping.com.rev";
        allow-update { none; };
};

辅助DNS设置

定义DNS服务器监听地址

[root@b ~]# cat /etc/named.caching-nameserver.conf
options {
        listen-on port 53 { 192.168.0.201; };
        directory       "/var/named";
        dump-file       "/var/named/data/cache_dump.db";
        statistics-file "/var/named/data/named_stats.txt";
        memstatistics-file "/var/named/data/named_mem_stats.txt";
};
logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};
view localhost_resolver {
        recursion yes;
        include "/etc/named.rfc1912.zones";
};

配置辅助解析域

[root@b ~]# cat /etc/named.rfc1912.zones

zone "liusuping.com" IN {
        type slave;
        file "slaves/liusuping.com.zone";
        masters { 192.168.0.200;} ;
};

zone "0.168.192.in-addr.arpa" IN {
        type slave;
        file "slaves/liusuping.com.rev";
        masters { 192.168.0.200 ;};
};

启动named服务

[root@b ~]# service named restart
停止 named：[确定]
启动 named：[确定]
[root@b ~]#

测试辅助DNS

[root@b ~]# nslookup
> server 192.168.0.201
Default server: 192.168.0.201
Address: 192.168.0.201#53
> www.liusuping.com
Server:         192.168.0.201
Address:        192.168.0.201#53

Name:   www.liusuping.com
Address: 192.168.0.200
> 192.168.0.200
Server:         192.168.0.201
Address:        192.168.0.201#53

200.0.168.192.in-addr.arpa      name = www.liusuping.com.
200.0.168.192.in-addr.arpa      name = dns.liusuping.com.

辅助DNS启动后会与主DNS服务器进行区域配置文件的同步，在/var/named/slaves/目录下会自动生成解析数据库

[root@b ~]# ls /var/named/slaves/ -l
总计 8
-rw-r--r-- 1 named named 389 08-10 21:57 liusuping.com.rev
-rw-r--r-- 1 named named 404 08-10 21:57 liusuping.com.zone

看下辅助DNS启动的载入过程，在日志中可以看到辅助DNS从主DNS辅助解析数据文件的过程。

Aug 10 21:57:08 b named[6581]: starting BIND 9.3.6-P1-RedHat-9.3.6-4.P1.el5_4.2 -u named -c /etc/named.caching-nameserver.conf
Aug 10 21:57:08 b named[6581]: adjusted limit on open files from 1024 to 1048576
Aug 10 21:57:08 b named[6581]: found 1 CPU, using 1 worker thread
Aug 10 21:57:08 b named[6581]: using up to 4096 sockets
Aug 10 21:57:08 b named[6581]: loading configuration from '/etc/named.caching-nameserver.conf'
Aug 10 21:57:08 b named[6581]: using default UDP/IPv4 port range: [1024, 65535]
Aug 10 21:57:08 b named[6581]: using default UDP/IPv6 port range: [1024, 65535]
Aug 10 21:57:08 b named[6581]: listening on IPv4 interface eth0, 192.168.0.201#53
Aug 10 21:57:08 b named[6581]: command channel listening on 127.0.0.1#953
Aug 10 21:57:08 b named[6581]: command channel listening on ::1#953
Aug 10 21:57:08 b named[6581]: the working directory is not writable
Aug 10 21:57:08 b named[6581]: zone 0.in-addr.arpa/IN/localhost_resolver: loaded serial 42
Aug 10 21:57:08 b named[6581]: zone 0.0.127.in-addr.arpa/IN/localhost_resolver: loaded serial 1997022700
Aug 10 21:57:08 b named[6581]: zone 255.in-addr.arpa/IN/localhost_resolver: loaded serial 42
Aug 10 21:57:08 b named[6581]: zone localdomain/IN/localhost_resolver: loaded serial 42
Aug 10 21:57:08 b named[6581]: zone localhost/IN/localhost_resolver: loaded serial 42
Aug 10 21:57:08 b named[6581]: running
Aug 10 21:57:08 b named[6581]: zone 0.168.192.in-addr.arpa/IN/localhost_resolver: Transfer started.
Aug 10 21:57:08 b named[6581]: transfer of '0.168.192.in-addr.arpa/IN' from 192.168.0.200#53: connected using 192.168.0.201#46038
Aug 10 21:57:08 b named[6581]: zone 0.168.192.in-addr.arpa/IN/localhost_resolver: transferred serial 1997022700
Aug 10 21:57:08 b named[6581]: transfer of '0.168.192.in-addr.arpa/IN' from 192.168.0.200#53: end of transfer
Aug 10 21:57:08 b named[6581]: zone 0.168.192.in-addr.arpa/IN/localhost_resolver: sending notifies (serial 1997022700)
Aug 10 21:57:09 b named[6581]: zone liusuping.com/IN/localhost_resolver: Transfer started.
Aug 10 21:57:09 b named[6581]: transfer of 'liusuping.com/IN' from 192.168.0.200#53: connected using 192.168.0.201#38146
Aug 10 21:57:09 b named[6581]: zone liusuping.com/IN/localhost_resolver: transferred serial 42
Aug 10 21:57:09 b named[6581]: transfer of 'liusuping.com/IN' from 192.168.0.200#53: end of transfer
Aug 10 21:57:09 b named[6581]: zone liusuping.com/IN/localhost_resolver: sending notifies (serial 42)

注意：在配置过程可能会出现一些错误，如果你配置和上面的过程一样，可能是你文件或目录的权限没设置对，或者系统防火墙的设置问题，可以参考 [Redhat Linux DNS服务软件两个故障的排错]

转发DNS配置

当DNS服务器在收到DNS客户端的查询请求后，它将在所管辖区域的数据库中寻找是否有该客户端的数据。如果该DNS服务器的区域数据库中没有该客户端的数据（即在DNS服务器所管辖的区域数据库中并没有该DNS客户端所查询的主机名）时，该DNS服务器需转向其他的DNS服务器进行查询。

有了转发器后，当DNS客户端提出查询请求时，DNS服务器将通过转发器从外界DNS服务器中获得数据，并将其提供给DNS客户端。

在bind中可以将服务器设置为转发DNS服务器，可以选择转发全部DNS请求，只需要修改一下“/etc/named.caching-nameserver.conf ”

options {
        forward only;
        forwarders {192.168.0.231;}; //定义向哪台服务器转发DNS请求。
#       listen-on port 53 { 192.168.0.232; };
#       listen-on-v6 port 53 { ::1; };
#       directory       "/var/named";
#       dump-file       "/var/named/data/cache_dump.db";
#        statistics-file "/var/named/data/named_stats.txt";
#        memstatistics-file "/var/named/data/named_mem_stats.txt";
#       query-source    port 53;
#       query-source-v6 port 53;
#       allow-query     { localhost; };
};
logging {
        channel default_debug {
                file "data/named.run";
                severity dynamic;
        };
};
# view localhost_resolver {
#       match-clients      { localhost; };
#       match-destinations { localhost; };
#       recursion yes;
#       include "/etc/named.rfc1912.zones";
#};

当然也可以选择只转发部分域的DNS请求，在/etc/named.rfc1912.zones中进行修改，增加一个名为 liusuping.com 的域，将该域的查询转发到192.168.0.231

zone "liusuping.com" {
        type forward;
        forwarders { 192.168.0.231;};
};

转载请注明：

本文转自：http://www.liusuping.com/ubuntu-linux/Redhat-Linux-BIND-DNS-fuzhu.html