1. Presented By- Satyam Pandey
Reg No.- 11103875

2. 
 Network addresses are numbers.
 Addresses are topologically oriented
Used for routing purposes
Moving a host may require change of address
Are not easy to remember
 Names can be used for users and for applications
Easy for humans
Can be used as a low level service discovery mechanism.
Changing the server machine requires just changing the name-> IP binding
Names can have a logical structure.
REQUIREMENT OF DNS

3. 
 In the beginning, there was the hosts.txt
-A file containing the names and addresses of all hosts in the network
-Problems: maintainability, size
-Still used as a backup (local network host information)
 DNS
– Tree-structured
– Delegation
– Separated from network structure and topology
– uses UDP, port number 53 for queries, TCP for zone transfers.
HISTORY

4. 
Terms:
-namespace = set of possible names, flat or hierarchical.
-naming system maintains a collection of bindings of names to values.
-given a name, a resolution mechanism returns the corresponding value.
-a name server is an implementation of the resolution mechanism.
-DNS (Domain Name System) = name service in Internet.
-Zone is an administrative unit, domain is a subtree.
DNS System

5. 
First level hierarchy
-- domains for each country + edu., com., gov., mil., org., net., int.
– New domains: aero., biz., coop., info., museum., name., pro.
– DNS first level managed by Internet Corporation for Assigned Names
& Numbers (ICANN), also manages address allocations.
Hierarchy is partitioned into subtrees, zones
-- zone corresponds to administrative boundaries in DNS (and, often also of
DNS-servers).
DNS Domain Hierarchy

7. 
1. Global Distribution
 Data is maintained locally, but retrievable globally
 No single computer has all DNS data
 DNS lookups can be performed by any device
 Remote DNS data is locally catchable to improve performance.
2. Loose Coherency
 Changes to the master copy of the database are replicated according to
timing set by the zone administrator.
 Cached data expires according to timeout set by zone administrator
DNS features

8. 
3. Scalability
 No limit to the size of the database
 No limit to the number of queries
-- 24,000 queries per second handled easily
 Queries distributed among masters, slaves, and caches
4. Reliability
 Data is replicated
--Data from master is copied to multiple slaves
 Clients can query
 Clients will typically query local caches
 DNS protocols can use either UDP or TCP
Contd…

9. 
5. Dynamicity
 Database can be updated dynamically
 Modification of the master database triggers replication
 Only master can be dynamically updated
Contd….

10. 
 Name servers store information about the name space in units
called “zones”.
 Usually, more than one name server are authoritative for the same
zone
 Also, a single name server may be authoritative for many zones
Types of Name Server
1.Authoritative – maintains the data
 Master – where the data is edited
 Slave – where data is replicated to
2. Caching – stores data obtained from an authoritative server.
Name Servers and Zones

11. 
Name Server and Zones

12. 
Questions?