在CentOS 5.5中配置DNS服务器，可以按照以下步骤进行：

1、安装BIND软件包

需要安装BIND软件包，它是用于实现DNS服务的主要工具，可以使用以下命令安装：

 sudo yum install bind bindutils y

2、备份原始配置文件

在修改配置文件之前，建议先备份原始的/etc/named.conf文件：

 sudo cp /etc/named.conf /etc/named.conf.bak

3、编辑主配置文件

使用文本编辑器打开/etc/named.conf文件，例如使用vi编辑器：

 sudo vi /etc/named.conf

在文件中添加以下内容：

 options {     listenon port 53 { any; };     directory       "/var/named";     dumpfile       "/var/named/data/cache_dump.db";     statisticsfile "/var/named/data/named_stats.txt";     memstatisticsfile "/var/named/data/named_mem_stats.txt";     allowquery     { any; };     recursion yes; }; logging {     channel default_debug {         file "data/named.run";         severity dynamic;     }; }; zone "." IN {     type hint;     file "named.ca"; }; include "/etc/named.rfc1912.zones"; include "/etc/named.root.key";

4、创建区域文件目录

创建一个新的目录来存放区域文件：

 sudo mkdir /var/named/example.com

5、创建正向查找区域文件

在刚刚创建的目录下创建一个名为example.com.zone的文件，并添加以下内容：

 $TTL    86400 @       IN      SOA     ns1.example.com. admin.example.com. (                               3         ; Serial                         604800         ; Refresh                           86400         ; Retry                         2419200         ; Expire                          86400 )       ; Negative Cache TTL ; Name servers for the zone example.com: NS records are listed here, separated by spaces or tabs, and each must be on a separate line. The name server names should be specified in reverse order, i.e., the first name server listed is the one that should be contacted first for resolution of host names within the zone. If there are multiple name servers listed, they should be separated by commas or semicolons, with no spaces in between. For example: @       IN      NS      ns1.example.com. ns2.example.com. ns3.example.com.; A records are listed here, separated by spaces or tabs, and each must be on a separate line. Each record consists of a domain name and an IP address, separated by a space or a tab, and terminated by a semicolon (;). For example: @       IN      A       192.168.1.1; CNAME records are listed here, separated by spaces or tabs, and each must be on a separate line. Each record consists of a domain name and an alias, separated by a space or a tab, and terminated by a semicolon (;). For example: mail IN      CNAME    example.com; NS records are listed here, separated by spaces or tabs, and each must be on a separate line. The name server names should be specified in reverse order, i.e., the first name server listed is the one that should be contacted first for resolution of host names within the zone. If there are multiple name servers listed, they should be separated by commas or semicolons, with no spaces in between. For example: @       IN      NS      ns1.example.com. ns2.example.com. ns3.example.com.; SOA records are listed here, separated by spaces or tabs, and each must be on a separate line. Each record consists of several fields separated by spaces or tabs, and terminated by a semicolon (;). For example: @       IN      SOA     ns1.example.com. admin.example.com. ( ... ); Other resource records can also be listed here as needed, such as MX records for mail exchangers, PTR records for reverse mapping of IP addresses to domain names, etc

下面是一个简化的介绍，展示了在CentOS 5.5系统上配置DNS服务器的基本步骤和配置项。

以下是具体配置的详细介绍：

请确保在配置文件中使用正确的域名、IP地址和序列号等，每次修改DNS配置后，需要检查配置文件的语法，并重新启动DNS服务：

 namedcheckconf service named restart