Transcript Name Services

Name Services
Jessie Crane
CPSC 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
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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
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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
References
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Albitz, Paul and Liu Crickel, “DNS and BIND.” O’Reilly &
Associates, Inc., 2001.
Blanchfield, Sean, An Anonymous and Scaleable Distributed Peerto-Peer System.” University of Dublin, 2002.
Galli, Doreen L., “Distributed Operating Systems.” Prentice Hall,
2000.
Hauben, Micheal, “History of ARPAnet.”
http://www.dei.isep.ipp.pt/docs/arpa.html, 2000.
Yuan, Fei and Li, Xuhui, “Hybrid Searching Algorithm for LooselyControlled Peer-to-Peer System.” University of Waterloo, 2002.