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This Concept Map, created with IHMC CmapTools, has information related to: Slides, DNS Internet Domain Name System includes DNS - The Internet Domain Name System A distributed naming database Name structure reflects administrative structure of the Internet Rapidly resolves domain names to IP addresses exploits caching heavily typical query time ~100 milliseconds Scales to millions of computers partitioned database caching Resilient to failure of a server replication, DNS Internet Domain Name System includes Directory and discovery services Directory service:- 'yellow pages' for the resources in a network Retrieves the set of names that satisfy a given description e.g. X.500, LDAP, MS Active Directory Services (DNS holds some descriptive data, but: the data is very incomplete DNS isn't organised to search it) Discovery service:- a directory service that also: is automatically updated as the network configuration changes meets the needs of clients in spontaneous networks (Section 2.2.3) discovers services required by a client (who may be mobile) within the current scope, for example, to find the most suitable printing service for image files after arriving at a hotel. Examples of discovery services: Jini discovery service, the 'service location the 'simple service discovery protocol' (part of UPnP), the 'secure discovery service'., DNS Internet Domain Name System includes DNS - The Internet Domain Name System A distributed naming database Name structure reflects administrative structure of the Internet Rapidly resolves domain names to IP addresses exploits caching heavily typical query time ~100 milliseconds Scales to millions of computers partitioned database caching Resilient to failure of a server replication, The role of names and name services Resources are accessed using identifier or reference An identifier can be stored in variables and retrieved from tables quickly Identifier includes or can be transformed to an address for an object E.g. NFS file handle, Corba remote object reference A name is human-readable value (usually a string) that can be resolved to an identifier or address Internet domain name, file pathname, process number E.g ./etc/passwd, http://www.cdk3.net/ For many purposes, names are preferable to identifiers because the binding of the named resource to a physical location is deferred and can be changed because they are more meaningful to users Resource names are resolved by name services to give identifiers and other useful attributes and Non-recursive and recursive server-controlled navigation DNS offers recursive navigation as an option, but iterative is the standard technique. Recursive navigation must be used in domains that limit client access to their DNS information for security reasons., The role of names and name services Resources are accessed using identifier or reference An identifier can be stored in variables and retrieved from tables quickly Identifier includes or can be transformed to an address for an object E.g. NFS file handle, Corba remote object reference A name is human-readable value (usually a string) that can be resolved to an identifier or address Internet domain name, file pathname, process number E.g ./etc/passwd, http://www.cdk3.net/ For many purposes, names are preferable to identifiers because the binding of the named resource to a physical location is deferred and can be changed because they are more meaningful to users Resource names are resolved by name services to give identifiers and other useful attributes and DNS Internet Domain Name System, Requirements for name spaces Allow simple but meaningful names to be used Potentially infinite number of names Structured to allow similar subnames without clashes to group related names Allow re-structuring of name trees for some types of change, old programs should continue to work Management of trust includes Service discovery in Jini Jini services register their interfaces and descriptions with the Jini lookup services in their scope Clients find the Jini lookup services in their scope by IP multicast Jini lookup service searches by attribute or by interface type The designers of Jini argue convincingly that this the only reliable way to do discovery, Requirements for name spaces Allow simple but meaningful names to be used Potentially infinite number of names Structured to allow similar subnames without clashes to group related names Allow re-structuring of name trees for some types of change, old programs should continue to work Management of trust includes Revision: Spontaneous networks Easy connection of guest's devices wireless network automatic configuration Easy integration with local services discovery of services relevant to guest's needs, DNS Internet Domain Name System includes DNS - The Internet Domain Name System A distributed naming database Name structure reflects administrative structure of the Internet Rapidly resolves domain names to IP addresses exploits caching heavily typical query time ~100 milliseconds Scales to millions of computers partitioned database caching Resilient to failure of a server replication, DNS Internet Domain Name System functions DNS server functions and configuration Main function is to resolve domain names for computers, i.e. to get their IP addresses caches the results of previous searches until they pass their 'time to live' Other functions: get mail host for a domain reverse resolution - get domain name from IP address Host information - type of hardware and OS Well-known services - a list of well-known services offered by a host Other attributes can be included (optional), DNS server functions and configuration Main function is to resolve domain names for computers, i.e. to get their IP addresses caches the results of previous searches until they pass their 'time to live' Other functions: get mail host for a domain reverse resolution - get domain name from IP address Host information - type of hardware and OS Well-known services - a list of well-known services offered by a host Other attributes can be included (optional) issues DNS issues Name tables change infrequently, but when they do, caching can result in the delivery of stale data. Clients are responsible for detecting this and recovering Its design makes changes to the structure of the name space difficult. For example: merging previously separate domain trees under a new root moving subtrees to a different part of the structure (e.g. if Scotland became a separate country, its domains should all be moved to a new country-level domain. See Section 9.4 on GNS, a research system that solves the above issues., The role of names and name services Resources are accessed using identifier or reference An identifier can be stored in variables and retrieved from tables quickly Identifier includes or can be transformed to an address for an object E.g. NFS file handle, Corba remote object reference A name is human-readable value (usually a string) that can be resolved to an identifier or address Internet domain name, file pathname, process number E.g ./etc/passwd, http://www.cdk3.net/ For many purposes, names are preferable to identifiers because the binding of the named resource to a physical location is deferred and can be changed because they are more meaningful to users Resource names are resolved by name services to give identifiers and other useful attributes and Requirements for name spaces Allow simple but meaningful names to be used Potentially infinite number of names Structured to allow similar subnames without clashes to group related names Allow re-structuring of name trees for some types of change, old programs should continue to work Management of trust, Requirements for name spaces Allow simple but meaningful names to be used Potentially infinite number of names Structured to allow similar subnames without clashes to group related names Allow re-structuring of name trees for some types of change, old programs should continue to work Management of trust includes Iterative navigation Used in: DNS: Client presents entire name to servers, starting at a local server, NS1. If NS1 has the requested name, it is resolved, else NS1 suggests contacting NS2 (a server for a domain that includes the requested name). NFS: Client segments pathnames (into 'simple names') and presents them one at a time to a server together with the filehandle of the directory that contains the simple name., Requirements for name spaces Allow simple but meaningful names to be used Potentially infinite number of names Structured to allow similar subnames without clashes to group related names Allow re-structuring of name trees for some types of change, old programs should continue to work Management of trust includes Summary Name services: defer the binding of resource names to addresses (and other attributes) Names are resolved to give addresses and other attributes Goals : Scalability (size of database, access traffic (hits/second), update traffic) Reliability Trust management (authority of servers) Issues exploitation of replication and caching to achieve scalability without compromising the distribution of updates navigation methods Directory and discovery services: 'yellow pages' retrieval by attributes dynamic resource registration and discovery