OPTION section It is the first section of the named.conf User can use only one option statement and many option-value pair under the section. Syntax is : option{ value "property"; } For eg : option { directory "/var/named"; dump file "/var/named/data/cache_drop.db"; statics file "/var/named/data/named_stats.txt"; }

Some option-values are as follows : 1. allow-query : accepts query from hosts in the "address- list" / accept-list 2. allow-transfer : zone transfer allow only by hosts usage 3. directory : path of directory where server configuration files are located. 4. files : limit no of concurrently open file.

5. check-names : host names are checked against the RPC usage. 6. cleaning interval “number”: time period to clean the expired records. 7. multiple cnames “no” : use of multiple names. 8. notify : when zone files are updated this option is set to yes.

9. forward : if set to first the servers listed in the forward option are queried and then server tries to find the answer itself.(first/only). 10. forwarders : shows IP addresses of servers to forward queries.

INCLUDE section Use to list the path and name of any file that user wants to include. Syntax is : Include “file path”; Eg : Include /etc/made.key

ACL section This section is use to specify list of IP addresses as an access control list.

Logging section Whenever user wants to use server logging option, the logging section is used. The channel is where we specify the location of the logged info. The logged info can be a returned file or a syslog.

Syntax : Logging { Channel channel name{ File path; Version number; Size in bytes; }

Category is used where user can specify the type of info in the log. Also severity level and print info can be specified. Category can be declared as : Category security{ Channel name “abc”; }

Category security{ Channel name “abc”; } Channel abc { syslog /var/log/syslog; print-time yes; print-category yes; }

Server section User can set the properties of the remote server where user can also specify whether to send query to the remote server from client. 1. bogus : yes/no – specifies whether queries are sent to remote server or not. 2. transfer : allows the number of trasnfers. 3. transfer-format : specify whether you want one answer or many answers. 4. keys : specify key ID.

ZONE section Each zone statement begins the word zone followed by domain name/IP zone “.” IN { type master;} Here “IN” is a data class which stands for internet. Type can be either master or slave.

Name of zone files are specified. Eg: zone “localhost” IN { type master; file named.localhost; allow_update none; };

Few more options in zone section 1. allow-query : accepts dns query from the hosts specified in its address list. 2. allow-transfer : allows zone information to be transferred. 3. notify : receives DNS notify messages. 4. allow-update : specifies to update DNS database. 5. max-transfer-time-in : specifies maximum time slave would wait for zone transfer.

Forward zone file Contains resource records about IP addresses. IN tyit.example.com{ 42; serial 3H; refresh 15M; retry 1W; expiry 1D;) minimum NS tyit.example.com tyit.example.com

A zone file starts with SOA – service of authority. Refresh: the amount of time the server should wait before refreshing the data. Retry: amount of time the server should wait before attempting to contact the primary server if the attempt to the previous seerver failed.

Expire : if secondary server is unable to contact the primary master, the data expires. TTL : specifies time to live for the data. specifies how long the data should be hold in the cache.

Reverse Zone File When a domain name is mapped to IP, it is known as forward resolution. If a user finds name from an IP number it is known as reverse address resolution and in this case “reverse file” is used.

IN tyit.example.com{ 42; serial 3H; refresh 15M; retry 1W; expiry 1D;) minimum NS tyit.example.com tyit.example.com

zone in-addr.arpa { notify no; type master; file “named.ca”; };

Configuring Master server 1. Master or Primary DNS Server is the main DNS server of the network. 2. /etc/named.conf has to be modified. 3. following lines should ne added : 3.1 for forward lookup zone example.com IN{ notify no; type master; file “named.localhost”; };

3.2 for reverse lookup zone in-addr.arpa{ notify no; type master; file “named.loopback”; };

4. Names of file on master and slave server should be same. 5. user needs to create zone files which are referenced using /etc/named.conf 6. user needs to add name server and mail exchange information. 7. add information about name server and their IP addresses.

8. start the named service [root#] service named start 9. in /etc/host.conf – word bind should be there. 10. in /etc/nsswitch.conf hosts : file dns

11. write IP address of nameserver in /etc/resolv.conf nameserver restart the named service [root#[ service named restart 13. make it onboot [root#] chkconfig named on

Configuring Slave Server 1. Master or Primary DNS Server is the main DNS server of the network. 2. /etc/named.conf has to be modified. 3. following lines should ne added : 3.1 for forward lookup zone example.com IN{ notify no; type slave; master (IP address of master DNS); file “named.localhost”; };

3.2 for reverse lookup zone in-addr.arpa{ notify no; type slave; master (IP address of master DNS); file “named.loopback”; };

4. Names of file on master and slave server should be same. 5. user needs to create zone files which are referenced using /etc/named.conf 6. user needs to add name server and mail exchange information. 7. add information about name server and their IP addresses.

8. start the named service [root#] service named start 9. in /etc/host.conf – word bind should be there. 10. in /etc/nsswitch.conf hosts : file dns

11. write IP address of nameserver in /etc/resolv.conf nameserver restart the named service [root#[ service named restart 13. make it onboot [root#] chkconfig named on

Setting DNS Client First check the IP address of the name server It is in /etc/resolv.conf There are two ways to check the working of the configuration. 1. host program 2. dig program

Host program 1. host enables users to find out the IP addresses of the specified domain name. [root#] host tyit.example.com tyit.example.com has the IP address

2. to find out mail server and other information [root#] host –t mx tyit.example.com 3. for reverse mapping [root#] host tyit.example.com

Dig program Dig is used for debugging and finding other useful information. [root#] dig tyit.example.com Output : IP address is Domain name example.com Dns name tyit.example.com Server IP address

[root#] dig –x Domain name example.com Dns name tyit.example.com