How systems communicate in a network<\/h3>\n
In this example the computer-A is trying to view the site using the URL http:\/\/mycomp.com<\/p>\n
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The host ‘A’ contacts the DNS server to find the IP for ‘mycomp.com’, gets it from the DNS, and then contact the IP address for the web page.<\/p>\n
DNS Structure<\/h3>\n
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The Internet Corporation for Assigned Names and Number<\/h3>\n
The ICANN manages the DNS root of the Internet domain namespace. It\u2019s role is to manage the assignment of identifiers, and to ensuring that all users have unique names.<\/p>\n
DNS settings in client hosts<\/h3>\n<\/div>\n
In the client system, the IP address of a default DNS server has to be provided<\/p>\n
- \n
- \nIn a linux<\/strong> hosts the initial resolver is configured using the file \/etc\/resolve.conf<\/em><\/div>\n<\/li>\n
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In windows<\/strong> the default DNS server is configured in the TCP\/IP<\/em> settings<\/div>\n<\/li>\n<\/ul>\n\nTypes of Records in a DNS database<\/h3>\n
Types on entries\/records used in a DNS database are as follows:<\/p>\n<\/div>\n
- \n
- \nA record: Used to point a domain name to an IP address<\/div>\n<\/li>\n
- \n
PTR record: Used to point an IP to a domain name<\/div>\n<\/li>\n- \n
CNAME record: Used to point a domain name to another domain name<\/div>\n<\/li>\n- \n
MX record: Used to point to a mail server’s IP<\/div>\n<\/li>\n- \n
NS record: Points to its Name Server<\/div>\n<\/li>\n<\/ul>\nInstalling BIND DNS<\/h3>\n
Rpms that are required to install BIND DNS are:
\n1. Bind-9_ _ _.rpm
\n2. Caching_nameserver_ _ _.rpm
\n3. bind_utils_ _ _.rpm<\/p>\nConfiguration file :<\/strong> \/etc\/named.conf
\nDemon :<\/strong> named<\/p>\nWhere are the named log?<\/h3>\n
Transaction of BIND DNS by default are logged in \/var\/log\/messages
\nDetail logging can be enabled using the rndc utility.
\n# rndc querylog : This command is used to enable\/disable detail logs.
\n# service named status : This will output the status of logging too.<\/p>\nCreating a simple \/etc\/named.conf<\/h3>\n
# vi \/etc\/named.conf<\/p>\n
options {
\ndirectory “\/var\/named”;
\n};<\/p>\nzone “mycomp.com” {
\ntype master;
\nfile “mycomp_forward”;
\n};<\/p>\nzone “0.168.192.in-addr.arpa” {
\ntype master;
\nfile “mycomp_reverse”;
\n};<\/p>\nCheck for syntax errors in named.conf<\/h3>\n
The command named-checkconf \/etc\/named.conf <\/em><\/strong>with check for any syntax errors.
\nAny error caught will be displayed. Else will return to prompt<\/p>\nHow to create a forward database<\/h3>\n
The file localdomain.zone<\/em><\/strong> can be used as a template. Below listed templates are availanle if caching_nameserver is installed<\/p>\n
# cd \/var\/named\/
\n# cp localdomain.zone mycomp_forward
\n# vi mycomp_forward
\nAdd the following line:
\nsample.mycomp.com.<\/strong><\/span> \u00a0 IN \u00a0 A \u00a0 192.168.0.2<\/p>\nHow to create a reverse DNS database<\/h3>\n
# cd \/var\/named\/
\n# cp named.local mycomp_reverse
\n# vi mycomp_reverse
\nAdd the following line:
\n2 \u00a0 IN \u00a0 PTR \u00a0 sample.mycomp.com.<\/span><\/strong><\/p>\nHow to check for syntax errors in database<\/h3>\n
The command named-checkzone can be used<\/p>\n
#] named-checkzone mycomp.com \/var\/named\/mycomp_forward
\nzone mycomp.com\/IN: loaded serial 42
\nOK
\n#]<\/p>\n- \n
- Any error caught will be displayed.<\/li>\n
- Else will return to prompt with the serial number.<\/li>\n<\/ul>\n
DNS: Master\/Slave<\/h3>\n
Here one DNS server will work as the master. All updates will be made in master DNS
\nSlave DNS pulls info from master frequently.<\/p>\nHow to configure a slave DNS<\/h3>\n
The configuration file \/etc\/named.conf<\/strong><\/em> of a simple slave DNS server:<\/p>\n
options {
\ndirectory “\/var\/named” ;
\n};<\/p>\nzone “mycomp.com” {
\ntype slave ;
\nfile “mycomp_forward” ;
\nmasters {10.146.179.68; } ;
\n};<\/p>\nOnce you start the DNS server this slave host will contact the master (10.146.179.68) and make a copy of sample_forward file the local host. So if this file appears in the slave host, it shows the transfer happened correctly.<\/p>\n
Reasons why slave DNS cannot update its database from the master server<\/h3>\n
- \n
- Check for an entry allow-transfer in the named.conf file in the master DNS server<\/li>\n
- Ensure the named.conf files, and the folder \/var\/named is owned by the user and group named.<\/li>\n
- The SELINUX \/ Iptables could create issues.<\/li>\n<\/ul>\n
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