DNS configuration in linux
Here i am giving you a basic idea about DNS (bind) configuration in linux server's . I have configured the bind package in Cent OS 5.4 version .
1. First we will check main packages required for bind configuration. I am listing the package names below
a. bind-9.3.4-10.pl.el5
b.bind-libs-9.3.4-10.pl.el5
c.bind-chroot-9.3.4.-10.pl.el5
| File | Purpose | BIND chroot Location | Regular BIND Location |
|---|---|---|---|
| named.conf | Tells the names of the zone files to be used for each of your website domains. | /var/named/chroot/etc | /etc |
| rndc.key
rndc.conf
| Files used in named authentication | /var/named/chroot/etc | /etc |
| zone files | Links all the IP addresses in your domain to their corresponding server | /var/named/chroot/var/named | /var/named |
4. Here as per our configuration zone files are vm.linux.com.zone ( forward lookup zone) and 0.1.168.192.in.addr.arpa (reverse lookup zone).
As per this configuration you can see the TTL ( time to leave ) value is 86400 seconds . This value indicates the time where the caching name server's will keep the answer from authority server , so the load to the authority server will be reduced .
Details of the forward look up zone file configuration is given bellow
| Field | Description |
|---|---|
| Name | The root name of the zone. The “@” sign is a shorthand reference to the current origin (zone) in the /etc/named.conf file for that particular database file. |
| Class | There are a number of different DNS classes. Home/SOHO will be limited to the IN or Internet class used when defining IP address mapping information for BIND. Other classes exist for non Internet protocols and functions but are very rarely used. |
| Type | The type of DNS resource record. In the example, this is an SOA resource record. Other types of records exist, which I’ll cover later. |
| Name-server | Fully qualified name of your primary name server. Must be followed by a period. |
| Email-address | The e-mail address of the name server administrator. The regular @ in the e-mail address must be replaced with a period instead. The e-mail address must also be followed by a period. |
| Serial-no | A serial number for the current configuration. You can use the date format YYYYMMDD with an incremented single digit number tagged to the end. This will allow you to do multiple edits each day with a serial number that both increments and reflects the date on which the change was made. |
| Refresh | Tells the slave DNS server how often it should check the master DNS server. Slaves aren’t usually used in home / SOHO environments. |
| Retry | The slave’s retry interval to connect the master in the event of a connection failure. Slaves aren’t usually used in home / SOHO environments. |
| Expiry | Total amount of time a slave should retry to contact the master before expiring the data it contains. Future references will be directed towards the root servers. Slaves aren’t usually used in home/SOHO environments. |
| Minimum-TTL | There are times when remote clients will make queries for subdomains that don’t exist. Your DNS server will respond with a no domain or NXDOMAIN response that the remote client caches. This value defines the caching duration your DNS includes in this response. |
Different types of records on forward look up zone file is given bellow
| Record Type | Name Field | Class Field2 | Type Field | Data Field |
|---|---|---|---|---|
| NS | Usually blank1 | IN | NS | IP address or CNAME of the name server |
| MX | Domain to be used for mail. Usually the same as the domain of the zone file itself. | IN | MX | Mail server DNS name |
| A | Name of a server in the domain | IN | A | IP address of server |
| CNAME | Server name alias | IN | CNAME | "A" record name for the server |
| PTR | Last octet of server’s IP address | IN | PTR | Fully qualified server name |
5. Same way reverse look up configuration file is also located in the same location ( in our case it will be 0.1.168.192.in.addr.arpa which is located at /var/named/chroot/var/named )
6. After configuring these zone files we can restart the named service as given below
7. Login to the different server which is located at the same network and add the name server details in /etc/resolve.conf file . Format is given below
8. After configuring the name server details you can test the DNS with below mentioned command
#dig FQDN ( Fully Qualified Domain Name) SOA
Sample output is given below
Your DNS configuration is successful .
