UniversityofHoustonApplicationsDatacomIILectureB.pptVIP

Datacomm II Spring 2002 University of HoustonApplicationsDatacom IILecture 12 B Dr Fred L Zellner fzellner@ Naming Outline Terminology Domain Naming System Distributed File Systems Overview What do names do? identify objects help locate objects define membership in a group specify a role convey knowledge of a secret Name space defines set of possible names consists of a set of name to value bindings Properties Names versus addresses Location transparent versus location-dependent Flat versus hierarchical Global versus local Absolute versus relative By architecture versus by convention Unique versus ambiguous Examples Hosts 7 7 80:23:A8:33:5B:9F Files /usr/llp/tmp/foo (server, fileid) Users Larry Peterson llp@ Examples (cont) Mailboxes Services nearby ps printer with short queue and 2MB Domain Naming System Hierarchy Name Name Servers Partition hierarchy into zones Resource Records Each name server maintains a collection of resource records (Name, Value, Type, Class, TTL) Name/Value: not necessarily host names to IP addresses Type NS: Value gives domain name for host running name server that knows how to resolve names within specified domain. CNAME: Value gives canonical name for particle host; used to define aliases. MX: Value gives domain name for host running mail server that accepts messages for specified domain. Class: allow other entities to define types TTL: how long the resource record is valid Root Server (, , NS, IN) (, 33, A, IN) (, , NS, IN) (, 0, A, IN) … Princeton Server (, , NS, IN) (, , A, IN) (, , NS, IN) (, 66, A, IN) (, , A, IN) (, , A, IN) (, , A, IN) (, , A, IN) CS Server (, , MX, IN) (, 0, A, IN) (, , CNAME, IN) (, , A, IN) (, , CNAME, IN) (, 5, A, IN) (, , CNAME, IN) Name Resolution Strategies forward iterative recursive Local server need to know root at only one place (not each host) site-wide cache Distributed File Systems No Transparency Global AFS: //usr/llp/tmp/foo Windows: f