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University of Houston Applications Datacom II Lecture 12 B

University of Houston Applications Datacom II Lecture 12 B. Dr Fred L Zellner fzellner@uh.edu. 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

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University of Houston Applications Datacom II Lecture 12 B

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  1. University of HoustonApplicationsDatacom IILecture 12 B Dr Fred L Zellner fzellner@uh.edu Datacomm II Spring 2002

  2. Naming Outline Terminology Domain Naming System Distributed File Systems Datacomm II Spring 2002

  3. 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 Datacomm II Spring 2002

  4. 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 Datacomm II Spring 2002

  5. Examples • Hosts cheltenham.cs.princeton.edu 192.12.69.17 192.12.69.17 80:23:A8:33:5B:9F • Files /usr/llp/tmp/foo (server, fileid) • Users Larry Peterson llp@cs.princeton.edu Datacomm II Spring 2002

  6. User 1 2 user @ cs.princeton.edu cs.princeton.edu Name Mail server program 4 192.12.69.5 192.12.69.5 3 TCP 192.12.69.5 5 IP Examples (cont) • Mailboxes • Services nearby ps printer with short queue and 2MB Datacomm II Spring 2002

  7. Domain Naming System • Hierarchy • Name chinstrap.cs.princeton.edu Datacomm II Spring 2002

  8. Root name server … Princeton Cisco name server name server … CS EE name server name server Name Servers • Partition hierarchy into zones edu com gov mil org net uk fr … … … … … princeton mit cisco yahoo nasa nsf arpa navy acm ieee cs ee physics ux01 ux04 • Each zone implemented by two or more name servers Datacomm II Spring 2002

  9. 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 Datacomm II Spring 2002

  10. Root Server (princeton.edu, cit.princeton.edu, NS, IN) (cit.princeton.edu, 128.196.128.233, A, IN) (cisco.com, thumper.cisco.com, NS, IN) (thumper.ciscoe.com, 128.96.32.20, A, IN) … Datacomm II Spring 2002

  11. Princeton Server (cs.princeton.edu, optima.cs.princeton.edu, NS, IN) (optima.cs.princeton.edu, 192.12.69.5, A, IN) (ee.princeton.edu, helios.ee.princeton.edu, NS, IN) (helios.ee.princeton.edu, 128.196.28.166, A, IN) (jupiter.physics.princeton.edu, 128.196.4.1, A, IN) (saturn.physics.princeton.edu, 128.196.4.2, A, IN) (mars.physics.princeton.edu, 128.196.4.3, A, IN) (venus.physics.princeton.edu, 128.196.4.4, A, IN) Datacomm II Spring 2002

  12. CS Server (cs.princeton.edu, optima.cs.princeton.edu, MX, IN) (cheltenham.cs.princeton.edu, 192.12.69.60, A, IN) (che.cs.princeton.edu, cheltenham.cs.princeton.edu, CNAME, IN) (optima.cs.princeton.edu, 192.12.69.5, A, IN) (opt.cs.princeton.edu, optima.cs.princeton.edu, CNAME, IN) (baskerville.cs.princeton.edu, 192.12.69.35, A, IN) (bas.cs.princeton.edu, baskerville.cs.princeton.edu, CNAME, IN) Datacomm II Spring 2002

  13. Root 2 name server cicada.cs.princeton.edu 3 princeton.edu, 128.196.128.233 4 1 Local Princeton cicada.cs.princeton.edu cicada.cs.princeton.edu name name Client server server cs.princeton.edu, 192.12.69.5 192.12.69.60 8 5 cicada.cs.princeton.edu 192.12.69.60 cicada.cs.princeton.edu, 6 CS name server 7 Name Resolution • Strategies • forward • iterative • recursive • Local server • need to know root at only one place (not each host) • site-wide cache Datacomm II Spring 2002

  14. Distributed File Systems • No Transparency Global AFS: /cs.princeton.edu/usr/llp/tmp/foo Windows: f:/usr/llp/tmp/foo • Transparency by Convention • NFS: /usr/llp/tmp/foo • Or Not: /n/fs/fac5/llp/tmp/foo • Transparency by Architecture • Sprite: /usr/llp/tmp/foo • Private versus Shared • ASF: /usr/llp/tmp/foo versus/afs/shared Datacomm II Spring 2002

  15. Stupid Naming Tricks • Symbolic links • Mount points • Union mounts • Per-User name spaces • Logical name spaces • Computed directories Datacomm II Spring 2002

  16. Abstract Syntax Notation OneASN.1 • Used to define format of PDUs • Representation of distributed information • Representation of operations performed on transmitted data Datacomm II Spring 2002

  17. Terms Relevant to ANS.1 • Abstract Syntax • Describes generic structure of data • Data Type • Named set of values • Encoding • Sequence of octets used to represent data value • Encoding Rules • Mapping from one syntax to another • Transfer Syntax • Way data represented in bit patterns while in transit Datacomm II Spring 2002

  18. Use of Abstract and Transfer Syntaxes Datacomm II Spring 2002

  19. ASN.1 Concepts • Module definition • Structured definition of a data structure using ASN.1 • Name of module used as abstract syntax name Datacomm II Spring 2002

  20. Form of Modules • <modulereference>DEFINITIONS::= BEGIN EXPORTS IMPORTS AssignmentsList End • EXPORTS • Definitions which may be imported by other modules • IMPORTS • Definitions to be imported from other modules • AssignmentList • Type assignments, value assignments, macro definitions • <name>::=<description> Datacomm II Spring 2002

  21. Lexical Conventions • Layout not significant • Comments delimited by pair of hyphens (--) at start and pair of hyphens or end of line end of comment • Identifiers, type references and module names consist of upper and lower case letters, digits and hyphens • Identifier starts with lower case letter • Type reference or module name begins with upper case letter • Built in type consists of all upper case letters Datacomm II Spring 2002

  22. Abstract Data Types • Collection of values • Simple • Atomic • No components • Structured • Has components • Tagged • Derived from other types • Other • Include CHOICE and ANY types (see later) Datacomm II Spring 2002

  23. Tag Classes (1) • Every data type (except CHOICE and ANY) has associated tag • Universal • Generally useful • Application independent • Defined in standard • e.g. Boolean, Integer, Real Datacomm II Spring 2002

  24. Tag Classes (2) • Application wide • Relevant to particular application • Context specific • Relevant to particular application • Applicable in limited context • Private • User defined Datacomm II Spring 2002

  25. CHOICE and ANY • Data types without tags • When value assigned, type also assigned • Type assigned at run time • CHOICE • List of alternative known types • Only one type used to create value • ANY • Arbitrary value • Arbitrary type Datacomm II Spring 2002

  26. Subtypes (1) • Derived from parent type • Restricted subset of values • May be nested • Single value subtype • Explicit listing of all valid values • Contained subtype • Used to form new subtype from existing subtypes • Includes all values of subtypes it contains • Value range subtype • Real and Integer only • Specify endpoints of range Datacomm II Spring 2002

  27. Subtypes (2) • Permitted alphabet constraint • Only character string • All values that can be constructed using sub-alphabet • Size constrained • Limits number of items in type • e.g. number of bits in bit type • Inner type constraint • Applied to SEQUENCE, SEQUENCE OF, SET, SET OF, CHOICE • Only values from parent that satisfy one or more contraints Datacomm II Spring 2002

  28. PDU Example (part 1) Datacomm II Spring 2002

  29. PDU Example (part 2) Datacomm II Spring 2002

  30. PDU Example (part 3) Datacomm II Spring 2002

  31. Network Management - SNMP • Simple Network Management Protocol • Networks are becoming indispensable • More complexity makes failure more likely • Require automatic network management tools • Standards required to allow multi-vendor networks • Covering: • Services • Protocols • Management information base (MIB) Datacomm II Spring 2002

  32. Network Management Systems • Collection of tools for network management • Single operator interface • Powerful, user friendly command set • Performing most or all management tasks • Minimal amount of separate equipment • i.e. use existing equipment • View entire network as unified architecture • Active elements provide regular feedback Datacomm II Spring 2002

  33. Key Elements • Management station or manager • Agent • Management information base • Network management protocol Datacomm II Spring 2002

  34. Management Station • Stand alone system or part of shared system • Interface for human network manager • Set of management applications • Data analysis • Fault recovery • Interface to monitor and control network • Translate manager’s requirements into monitoring and control of remote elements • Data base of network management information extracted from managed entities Datacomm II Spring 2002

  35. Agent • Hosts, bridges, hubs, routers equipped with agent software • Allow them to be managed from management station • Respond to requests for information • Respond to requests for action • Asynchronously supply unsolicited information Datacomm II Spring 2002

  36. Management Information Base • MIB • Representation of network resources as objects • Each object a variable representing one aspect of managed object • MIB is collection of access points at agent for management of station • Objects standardized across class of system • Bridge, router etc. Datacomm II Spring 2002

  37. Network Management Protocol • Link between management station and agent • TCP/IP uses SNMP • OSI uses Common Management Information Protocol (CMIP) • SNMPv2 (enhanced SNMP) for OSI and TCP/IP Datacomm II Spring 2002

  38. Protocol Capabilities • Get • Set • Notify Datacomm II Spring 2002

  39. Management Layout • May be centralized in simple network • May be distributed in large, complex network • Multiple management servers • Each manages pool of agents • Management may be delegated to intermediate manager Datacomm II Spring 2002

  40. Example of Distributed Network Management Configuration Datacomm II Spring 2002

  41. SNMP v1 • August 1988 SNMP specification issued • Stand alone management stations and bridges, routers workstations etc supplied with agents • Defines limited, easily implemented MIB of scalar variables and two dimensional tables • Streamlined protocol • Limited functionality • Lack of security • SNMP v2 1993, revised 1996 • RFC 1901-1908 Datacomm II Spring 2002

  42. SNMP v2 (1) • Framework on which network management applications can be built • e.g fault management, performance monitoring, accounting • Protocol used to exchange management information • Each player maintains local MIB • Structure defined in standard • At least one system responsible for management • Houses management applications Datacomm II Spring 2002

  43. SNPM v2 (2) • Support central or distributed management • In distributes system, some elements operate as manager and agent • Exchanges use SNMP v2 protocol • Simple request/response protocol • Typically uses UDP • Ongoing reliable connection not required • Reduces management overhead Datacomm II Spring 2002

  44. SNMP v2 Managed Configuration Datacomm II Spring 2002

  45. Structure of Management Information • SMI • Defines general framework with which MIB defined and constructed • Identifies data types • How resources are represented and named • Encourages simplicity and extensibility • Scalars and two dimensional arrays of scalars (tables) only Datacomm II Spring 2002

  46. Protocol Operation • Exchange of messages • Outer message header deals with security • Seven types of PDU Datacomm II Spring 2002

  47. SNMP v2 PDU Formats Datacomm II Spring 2002

  48. SNMP v3 • Addresses security issues of SNMP v1/2 • RFC 2570-2575 • Proposed standard January 1998 • Defines overall architecture and security capability • To be used with SNMP v2 Datacomm II Spring 2002

  49. SNMP v3 Services • Authentication • Part of User-Based Security (UBS) • Assures that message: • Came from identified source • Has not been altered • Has not been delayed or replayed • Privacy • Encrypted messages using DES • Access control • Can configure agents to provide a number of levels of access to MIB • Access to information • Limit operations Datacomm II Spring 2002

  50. Electronic Mail • Most heavily used application on any network • Simple Mail Transfer Protocol (SMTP) • TCP/IP • Delivery of simple text messages • Multi-purpose Internet Mail Extension (MIME) • Delivery of other types of data • Voice, images, video clips Datacomm II Spring 2002

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