DOMAIN NAME SYSTEM(DNS)

Presented By- Satyam PandeyReg No.- 11103875

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

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

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

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

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

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…

5. Dynamicity Database can be updated dynamically Modification of the master database triggers replication Only master can be dynamically updated

Contd….

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

Name Server and Zones

Questions?