1. Naming
Chapter 4

2. Basic Naming Terminology
Name: A string of bits or characters that is used to refer to an entity (i.e. hosts, printers, disks, files).
Access point: An entity through which other entities in a distributed system are accessed.
Address: a special kind of name that refers to an access point of an entity.
An entity can
offer more than one access point.
change its access point

3. Separation an Entity from its Address
Changing an access point or reassigning an access point
Reorganizing a distributed system
Using an address to refer to an entity leads to invalid reference
Refer to the service by a name independent of the address of its access point
How to reference an entity that offers more than one access point
Web services that are distributed across several servers
Refer to the web service by a name independent of the addresses of its access points

4. Naming versus Locating Entities
Direct, single level mapping between names and addresses.
T-level mapping using identities.

5. Characteristics of an identifier
Identifiers: Names that are used to uniquely identify an entity
Properties of an identifier that helps to defines names that are location independent:
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

6. Flat Naming Broadcasting and Multicasting Forwarding Pointers
Applicable in LANs
Address Resolution Protocol (ARP)
Forwarding Pointers
When an entity moves from A to B it leaves a forwarding reference
SSP chains: when an object moves from address space A to B it leaves behind a client stub in A and installs a server stub that refers to it in B.
Home-based approaches
Hierarchical approaches

7. Forwarding Pointers (1)
The principle of forwarding pointers using (proxy, skeleton) pairs.

8. Forwarding Pointers (2)
Redirecting a forwarding pointer, by storing a shortcut in a proxy.

9. Home-Based Approaches
Home location keeps track of the current location of an entity
Mobile IP
Each mobile host uses a fixed IP
All communication to that entity is directed to the host’s home agent
This home agent is located on the LAN corresponding to the network address in the mobile host’s IP address
Drawback:
increased latency in large networks
Use of a fixed home location
Solution
register the home at a traditional naming service

10. Home-Based Approaches
The principle of Mobile IP.

11. Hierarchical Approaches (1)
Hierarchical organization of a location service into domains, each having an associated directory node.

12. Hierarchical Approaches (2)
An example of storing information of an entity having two addresses in different leaf domains.

13. Hierarchical Approaches (3)
Looking up a location in a hierarchically organized location service.

14. Hierarchical Approaches (4)
An insert request is forwarded to the first node that knows about entity E.
A chain of forwarding pointers to the leaf node is created.

15. Structured Naming Name Spaces Name space distribution
Implementing of name resolution
Domain Name System

16. A general naming graph with a single root node.
Name Spaces (1)
A general naming graph with a single root node.

17. Name Spaces (2)
The general organization of the UNIX file system implementation on a logical disk of contiguous disk blocks.

18. Linking and Mounting (1)
The concept of a symbolic link explained in a naming graph.

19. Linking and Mounting (2)
Mounting remote name spaces through a specific process protocol.

20. Linking and Mounting (3)
Organization of the DEC Global Name Service

21. Name Space Distribution (1)
An example partitioning of the DNS name space, including Internet-accessible files, into three layers.

22. Name Space Distribution (2)
Item
Global
Administrational
Managerial
Geographical scale of network
Worldwide
Organization
Department
Total number of nodes
Few
Many
Vast numbers
Responsiveness to lookups
Seconds
Milliseconds
Immediate
Update propagation
Lazy
Number of replicas
None or few
None
Is client-side caching applied?
Yes
Sometimes
A comparison between name servers for implementing nodes from a large-scale name space partitioned into a global layer, as an administrational layer, and a managerial layer.

23. Implementation of Name Resolution (1)
The principle of iterative name resolution.

24. Implementation of Name Resolution (2)
The principle of recursive name resolution.

25. Implementation of Name Resolution (3)
Server for node
Should resolve
Looks up
Passes to child
Receives and caches
Returns to requester cs
<ftp>
#<ftp> -- vu
<cs,ftp>
#<cs>
#<cs> #<cs, ftp> ni
<vu,cs,ftp>
#<vu>
#<cs> #<cs,ftp>
#<vu> #<vu,cs> #<vu,cs,ftp>
root
<ni,vu,cs,ftp>
#<nl>
#<nl> #<nl,vu> #<nl,vu,cs> #<nl,vu,cs,ftp>
Recursive name resolution of <nl, vu, cs, ftp>. Name servers cache intermediate results for subsequent lookups.

26. Implementation of Name Resolution (4)
The comparison between recursive and iterative name resolution with respect to communication costs.

27. The DNS Name Space
Type of record
Associated entity
Description
SOA
Zone
Holds information on the represented zone A
Host
Contains an IP address of the host this node represents MX
Domain
Refers to a mail server to handle mail addressed to this node
SRV
Refers to a server handling a specific service NS
Refers to a name server that implements the represented zone
CNAME
Node
Symbolic link with the primary name of the represented node
PTR
Contains the canonical name of a host
HINFO
Holds information on the host this node represents
TXT
Any kind
Contains any entity-specific information considered useful
The most important types of resource records forming the contents of nodes in the DNS name space.

28. An excerpt from the DNS database for the zone cs.vu.nl.
DNS Implementation (1)
An excerpt from the DNS database for the zone cs.vu.nl.

29. DNS Implementation (2)
Name
Record type
Record value
cs.vu.nl
NIS
solo.cs.vu.nl A
Part of the description for the vu.nl domain which contains the cs.vu.nl domain.

30. Attribute-based Naming
Abbr.
Value
Country C NL
Locality L
Amsterdam
Organization
Vrije Universiteit
OrganizationalUnit OU
Math. & Comp. Sc.
CommonName CN
Main server
Mail_Servers --
, ,
FTP_Server
WWW_Server
A simple example of a X.500 directory entry using X.500 naming conventions.

31. Part of the directory information tree.
The X.500 Name Space (1)
Part of the directory information tree.

32. Two directory entries having Host_Name as RDN.
The X.500 Name Space (2)
Attribute
Value
Country NL
Locality
Amsterdam
Organization
Vrije Universiteit
OrganizationalUnit
Math. & Comp. Sc.
CommonName
Main server
Host_Name
star
zephyr
Host_Address
Two directory entries having Host_Name as RDN.

33. References
Lecture slides of Distributed Systems principles and paradigms by
Andrew Tannenbaum and Van Steen, Prentice Hall India, 2002.