name services jessie crane cpsc 550. history arpanet – experimental computer network (late 1960s)...
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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
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
1. 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.