1. DNS

2. DNS is a network service that enables clients to resolve names to IP address and vice-versa. Allows machines to be logically grouped by domain names. Provides email routing information.

3. Internet Naming Hierarchy DNS The silent dot at the end of all addresses.com.net.org.in.sidbi www.ac.co.iitk www

4. DNS Operation DNS Setup A DNS server maintains the name to IP address mapping of the domain for which it is the name server. The DNS server for a domain is registered with the domain registrar and the entry is maintained by the Internet Root-Servers (13) or Country Level Root- Servers. Whenever a server is queried, if doesn’t have the answer, the root servers are contacted. The root servers refer to the DNS server for that domain (in case the domain is a top level domain) or the Country Root Server (in case the domain is country level domain).

5. DNS Configuration DNS Setup named daemon is used A DNS Server may be caching/master/slave server The named.ca file has information of all Root Servers. There is a Forward Zone file and a Reverse Zone file for every domain. Configuration file: /var/named/chroot/etc/named.conf Forward Zone File: /var/named/chroot/var/named/ Reverse Zone File: /var/named/chroot/var/named/

6. Sample Master named.conf DNS Setup zone "." { type hint; file "named.ca"; }; zone "0.0.127.in-addr.arpa" { type master; file "named.local"; allow-query {any;}; }; zone "iitk.ac.in" { type master; file "hosts.db"; allow-query {any;}; }; zone "95.200.203.IN-ADDR.ARPA" { type master; file "hosts.rev.203.200.95"; allow-query {any;}; }; zone "iitk.ernet.in" { type slave; file "hosts.iitk.ernet.in"; masters { 202.141.40.10; }; allow-query {any;};

7. Sample Forward Zone File DNS Setup $TTL 86400 @ IN SOA ns.iitk.ac.in. root.ns.iitk.ac.in. ( 200605091 ; Serial 10800 ; Refresh - 3 hours 3600 ; Retry - 1 hour 1209600 ;Expire - 1 week 43200 ) ; Minimum TTL for negative answers - 12 hours IN NS ns.iitk.ac.in. IN NS proxy.iitk.ac.in. IN MX 5 mail0.iitk.ac.in. IN MX 10 mail1.iitk.ac.in. IN MX 20 mail2.iitk.ac.in. $ORIGIN iitk.ac.in. ns IN A 203.200.95.142 mail IN A 203.200.95.144 proxy IN CNAME mail

8. Sample Reverse Zone File DNS Setup $TTL 86400 $ORIGIN 200.203.in-addr.arpa. 95 IN SOA ns1.iitk.ac.in. root.ns1.iitk.ac.in. ( 200605091 ; Serial 10800 ; Refresh - 5 minutes 3600 ; Retry - 1 minute 1209600 ; Expire - 1 weeks 43200 ) ; Minimum TTL for negative answers - 12 hours IN NS ns.iitk.ac.in. IN NS proxy.iitk.ac.in. $ORIGIN 95.200.203.in-addr.arpa. ; 142 IN PTR ns.iitk.ac.in. 144 IN PTR mail.iitk.ac.in.

9. Configuring Local Resolver DNS Setup /etc/resolv.conf server 127.0.0.1

10. Test DNS DNS Setup nslookup host dig Test your DNS with the following DNS diagnostics web site: dnsstuff.comdnsstuff.com

11. Advanced BIND Features DNS Setup Access List Round Robin Load Sharing Dynamic DNS Update

12. Access Control List DNS Setup ACL is a list of semi-colon separated IP addresses or networks. Create ACLs and apply directives on specified ACLs acl “mynetwork” { 172.31.0.0/16; 172.30.1.1; }; allow-query {mynetwork; }; allow-transfer {mynetwork; }; allow-update {mynetwork; };

13. Dynamic DNS Update DNS Setup Allows the DNS server to update the Name and IP address of hosts on the network. To disable DDNS, use the directive: allow-update {none; };

14. Round Robin Load Sharing DNS Setup Load Balancing can be achieved by use of multiple A records for the same name: wwwINA203.200.95.140 wwwINA203.200.95.141 wwwINA203.200.95.142