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This Concept Map, created with IHMC CmapTools, has information related to: ch9 name name, name services and the DNS: -names serivce- stores a collection of one or more nameing contexts, (sets of bindings between textual names and attributes for objects such as users, computers, services and remote objects -unification- resources managed by different services to use the same naming scheme -integration- to share and therefore name resources that were created in different administrative domains has 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 -aliases- the DNS allows a convenient name to be substituted for a more complicated one -naming domains- is a name sapce for which there exists a single overall administrative authority for assigning names within it -combining and customizing name spaces- DNS provides a global and homogeneous name space in which a given name refers to the sam entity, no matter which process on which computer looks up the name -merging, - heterogeneity, -customization, name services and the DNS: -names serivce- stores a collection of one or more nameing contexts, (sets of bindings between textual names and attributes for objects such as users, computers, services and remote objects -unification- resources managed by different services to use the same naming scheme -integration- to share and therefore name resources that were created in different administrative domains has DNS server functions and configurations: 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), name services and the DNS: -names serivce- stores a collection of one or more nameing contexts, (sets of bindings between textual names and attributes for objects such as users, computers, services and remote objects -unification- resources managed by different services to use the same naming scheme -integration- to share and therefore name resources that were created in different administrative domains has name resolution: name servers and navigation- DNS stores a very large database and is used by a large population will not store all of its naming info on a single computer, DNS specifies that each subset of its database is replicated in at least two failure independent servers -caching- is a key to a name service's performance and assists in maintaining the availability of both the name service and other services despite name server crashes DNS: had 3 major orginal shortcomings 1 it did not scale to large numbers of computers 2 local organizations wished to adminster their own naming systems 3 a general name service was needed -DNS name servers- the problems of scale are treated by a combo of partitioning the naming database and replicating and caching parts of it close to the points of need -navigation and query processing- a DNS client is called a resolver, it accepts queries, formats them into messages expected under the DNS protocol -resource records- zone data are stored by name servers in files in one of several fixed types of resource record -the BIND implementation of the DNS- the Berkeley Internet Name Domain is implementation of the DNS for computers running UNIX -discussion of the DNS- the DNS internet implementation achieves relatively short average response times for lookups, considering the amount of naming data and the scale of the networks involved, name services and the DNS: -names serivce- stores a collection of one or more nameing contexts, (sets of bindings between textual names and attributes for objects such as users, computers, services and remote objects -unification- resources managed by different services to use the same naming scheme -integration- to share and therefore name resources that were created in different administrative domains has requirements for name a 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, name services and the DNS: -names serivce- stores a collection of one or more nameing contexts, (sets of bindings between textual names and attributes for objects such as users, computers, services and remote objects -unification- resources managed by different services to use the same naming scheme -integration- to share and therefore name resources that were created in different administrative domains has 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.