Name Services

Jessie CraneCPSC 550

History

• ARPAnet – experimental computer network (late 1960s)

• hosts.txt – a file that contained all the information about every host on the network

• Single management domain

History

• TCP/IP standardized connectivity to ARPAnet for all computers (early 1980s)

• hosts.txt – traffic and load problems• – file consistency problems• Increasing number of users• NIC had no control over host names

History

• NIC called for a replacement of the current system– Centralized system– Single-host bottleneck

• Paul Mockapertis created the Domain Name Service (DNS) in 1984.– Distributed database– Hierarchical structure

Name Services

• Domain Name Service (DNS) – Maps domain names to IP addresses

• Global Name Service (GNS)– Maps global names to their attributes

• X500 directory service– Stores collections of bindings between names and

attributes– Looks up entries that match attribute-based specs

• Jini discovery service– Looks up objects according to attributes

Goals

• Objective – look up attributes of an object by providing the object’s name

• Handle very large name spaces• Have a long life • Have high availability• Fault tolerance• Tolerance of mistrust (GNS)

Definitions

• Names – refer to resources in a distributed system

• Name service – stores a collection of naming contexts– Resolves names, which makes communication

and resource sharing possible– Different resources use the same naming

scheme, such as a URL

Definitions

• Replication – the process of copying data from one computer to another

• Caching – storing previously looked up information

• Resolver – a library routine that creates queries and sends them to a name server

Features

• Name services look up attributes of an object by providing an object’s name.

• Hierarchical in structure

DNS Features

• Maps domain names to IP addresses– Mostly for host names and email addresses

• Elements of that allow worldly lookup– Hierarchical partitioning of the name database– Replication of the naming data– Caching

DNS Structure• This method ensures

subdirectories or files do not have the same name

• Similar to Unix file system• Tree with root set to null• Each node = root of subtree• Subtree = partition of

overall database• Decentralize administration

GNS Features & Structure

• Names– Directory names = ab/cd/ef/qwm– Value names = jessie.crane/password

• Replication and caching essential

X500 Features & Structure

• Directory services return attributes that match specified attr.

• Yellow pages service• Directory Information

Tree (DIT)• Replication and

caching

Jini Features & Structure

• Registers the services provided in a spontaneous networking environment

• Look-up service & Jini• Print from laptop

How to Use DNS

• Register a new domain – need to submit a DNS server name and address– Register with current DNS server– Configure new DNS server

• /etc/named.boot or /etc/named.conf

• URLs and email clients

How to Use Directory Services

• Done through and application interface• Examples:

– User logging into a system enters a name and password.

– User invoking a spell check on a document

How to Use Discovery Services

• Jini can go on a home computer• Storage for devices can run directly on the

PC– Digital cameras – store pictures– Cell phones – backup the phone book– Answering machine – store long messages– VCR – store video on hard disk

DNS Application

• BIND– Resolves Internet host names into IP addresses

and vice versa• Most name servers on the Internet run

BIND• Old versions of BIND allow DNS spoofing

attacks

Directory Service Application

• Active Directory Service Interfaces (ASDI)• Compose of interfaces used to access

directory services from different networks– adding new users– managing printers– locating resources in a distributed environment– Setting permissions on network resources

Discovery Service Application

• Google – finds pages that are openly available on the Web.

Significance of Points

• Use a distributed peer-to-peer system instead of DNS

• Main reason: do not have to worry about a server being down.

• Pros: – Computing power– Storage space

• Example: Napster

Summary

• DNS is very good and will probably be faster on average than a peer-to-peer system

• DNS not have as many security issues • Peer-to-peer no availability issue

References1. Albitz, Paul and Liu Crickel, “DNS and BIND.” O’Reilly &

Associates, Inc., 2001.2. Blanchfield, Sean, An Anonymous and Scaleable Distributed Peer-

to-Peer System.” University of Dublin, 2002.3. Galli, Doreen L., “Distributed Operating Systems.” Prentice Hall,

2000.4. Hauben, Micheal, “History of ARPAnet.” http://www.dei.isep.ipp

.pt/docs/arpa.html, 2000.5. Yuan, Fei and Li, Xuhui, “Hybrid Searching Algorithm for

Loosely-Controlled Peer-to-Peer System.” University of Waterloo, 2002.