DISTRIBUTED SYSTEMS Principles and Paradigms Second Edition ANDREW S. TANENBAUM MAARTEN VAN STEEN Chapter 5 Naming
DISTRIBUTED SYSTEMS Principles and Paradigms Second Edition ANDREW S. TANENBAUM MAARTEN VAN STEEN Chapter 5 Naming
Names, Identifiers, And Addresses
Properties of a true identifier:
An identifier refers to at most one entity.
Each entity is referred to by at most one identifier.
An identifier always refers to the same entity
Flat naming
Broadcasting e Multicasting
Solo per reti locali
Viene inviato un messaggio contenente un identificatore a tutte le macchine e viene richiesto a ciascuna di verificarne la corrispondenza
Es. ARP per capire la corrispondenza IP/Indirizzo ethernet
Flat naming
Forwarding pointers
Usato per entità mobili;
Quando un oggetto si sposta lascia nel punto di partenza un riferimento al punto di arrivo
Le catene di riferimenti possono diventare lunghe
Forwarding Pointers (1)
Figure 5-1. The principle of forwarding pointers using (client stub, server stub) pairs.
Forwarding Pointers (2)
Figure 5-2. Redirecting a forwarding pointer by storing a shortcut in a client stub.
Forwarding Pointers (3)
Figure 5-2. Redirecting a forwarding pointer by storing a shortcut in a client stub.
Home-Based Approaches
Figure 5-3. The principle of Mobile IP.
Distributed Hash Tables General Mechanism
Figure 5-4. Resolving key 26 from node 1 and key 12 from node 28 in a Chord system.
Hierarchical Approaches (1)
Figure 5-5. Hierarchical organization of a location service into domains, each having an associated directory node.
Name Space Distribution (1)
Figure 5-13. An example partitioning of the DNS name space, including Internet-accessible files, into three layers.
Name Space Distribution (2)
Figure 5-14. A comparison between name servers for implementing nodes from a large-scale name space partitioned into a global layer, an administrational layer, and a managerial layer.
Example: The Domain Name System
Figure 5-18. The comparison between recursive and iterative name resolution with respect to communication costs.
What are directory services?
http://www.ischool.washington.edu/mcdonald/courses/imt546_au04/pres-12.11/ActiveDirectoryFinal.ppt Shared Resources:
Servers,
Shared volumes,
Printers;
Applications Administration of:
Users
User/Group access
Network resources
Management of domains, applications, services, security policies, and just about everything else in your network. All Directory services use a hierarchical structure that stores information about objects on the network. What differentiates the various implementations are the types of objects that they track.
Basic Network Identity Services
Microsoft's Active Directory
Novell Directory Services (NDS)
Network Identity services are used to access user credentials, access rights, and permissions.
They are basically designed to link business applications to physical network devices.
x.500
X.500 is a series of computer networking standards covering electronic directory services. The X.500 series was developed by ITU-T, formerly known as CCITT.
The directory services were developed in order to support the requirements of X.400 electronic mail exchange and name lookup.
ISO was a partner in developing the standards, incorporating them into the Open Systems Interconnection suite of protocols. ISO/IEC 9594 is the corresponding ISO identification.
http://en.wikipedia.org/wiki/X.500
x.500
The protocols defined by X.500 include:
DAP (Directory Access Protocol)
DSP (Directory System Protocol)
DISP (Directory Information Shadowing Protocol)
DOP (Directory Operational Bindings Management Protocol)
Because these protocols used the OSI networking stack, a number of alternatives to DAP were developed to allow Internet clients to access to the X.500 Directory using the TCP/IP networking stack. The most well-known alternative to DAP is Lightweight Directory Access Protocol (LDAP).
http://en.wikipedia.org/wiki/X.500
The LDAP Name Space
130.37.21.11 -- WWW_Server 130.37.21.11 -- FTP_Server 130.37.24.6, 192.31.231,192.31.231.66 -- Mail_Servers Main server CN CommonName Math. & Comp. Sc. OU OrganizationalUnit Vrije Universiteit L Organization Amsterdam L Locality NL C Country Value Abbr. Attribute A simple example of a LDAP directory entry using LDAP naming conventions.
The LDAP Name Space
Part of the directory information tree.
The LDAP Name Space
192.31.231.66 Host_Address 192.31.231.42 Host_Address zephyr Host_Name star Host_Name Main server CommonName Main server CommonName Math. & Comp. Sc. OrganizationalUnit Math. & Comp. Sc. OrganizationalUnit Vrije Universiteit Organization Vrije Universiteit Organization Amsterdam Locality Amsterdam Locality NL Country NL Country Value Attribute Value Attribute Two directory entries having Host_Name as RDN.
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