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SNMP Management Information

SNMP Management Information. Prof. Choong Seon HONG. SNMP Management Information. Database contains information about the elements to be managed : MIB Each resource to be managed is represented by object MIB : structured collection of such object having the form of tree

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SNMP Management Information

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  1. SNMP Management Information Prof. Choong Seon HONG

  2. SNMP Management Information • Database contains information about the elements to be managed : MIB • Each resource to be managed is represented by object • MIB : structured collection of such object having the form of tree • Structure of Management Information (SMI) • Specified in RFC 1155 • Providing a standardized technique for defining the structure of a particular MIB • Providing a standardized technique for defining individual objects, including the syntax and the value of each object • Providing a standardized technique for encoding object values • SMI Data Type Additions To Structure of Management Information Version 2 (SMIv2) And Structure of Management Information Version 1 (SMIv1) :draft-perkins-smi-addition-00.txt • The new data types are Integer64, Unsigned64, Float, Double, and DiscUnion (discriminated union)

  3. Defining objects • MIB (Management Information Base) • a precise definition of the information accessible through a network management protocol • each device must use the format for displaying information that is defined by the MIB • RFC 1052 • define an extended MIB for use with SNMP and CMIS/CMIP • is no longer realistic • RFC 1065: “Structure and Identification of Management Information for TCP/IP based Internets (SMI)” • describe the syntax and type of information available in the MIB for TCP/IP networks • RFC 1066 • use the rules of the SMI • present the first version of the MIB for TCP/IP • known as MIB-I

  4. Defining objects • RFC 1155 (SMI) • RFC 1065 later was adopted by the IAB as a full standard • four primitive data type • INTEGER • 32bit value in two’s complement representation • -2147483648 ~ 2147483647 • OCTET STRING • zero or more octets • 0 ~ 255 • represent a text string • OBJECT IDENTIFIER • a sequence of integers • traverse a hierarchical MIB tree • NULL

  5. MIB Structure • Leaf objects of the tree to be actual managed objects to represent some resource, activity, or related information • Object identifier : a unique identifier for particular object type • Serving as name the object • internet OBJECT IDENTIFIER :: = { iso (1) org(3) dod (6) 1} • therefore, internet node’s object ID : 1.3.6.1 • four nodes under the internet node • directory • mgmt ----> mib-1, mib-2 • experimental • private • MIB tree (see fig. 5.1)

  6. Object Syntax • Universal types • UNIVERSAL class of ASN.1 consisting of application-independent data types for defining MIB objects • integer (UNIVERSAL 2) • octetstring (UNIVERSAL 4) • null (UNIVERSAL 5) • object identifier (UNIVERSAL 6) • sequence, sequence-of (UNIVERSAL 16) • Object ID consisting of sequence of integers • for example : object ID for tcpConnTable : 1.3.6.1.2.1.6.13 iso org dod internet mgmt mib-2 tcp tcpConnTable 1 3 6 1 2 1 6 13

  7. Object Syntax • Application-wide Types • APPLICATION class of ASN.1 consisting of data types that are relevant to a particular application • application wide data types defined in RFC 1155 • networkaddress : defined using CHOICE construct, ex) IP Address • ipaddress : 32-bit address using the format specified in IP • counter : non-negative integer that may be increamented but not decremented with maximum value of 2 23 - 1. If the counter reaches its maximum, it wraps around and starts from zero • gauge : non-negative integer that may increase or decrease with maximum value of 2 23 -1. If the counter reaches its maximum, it remains its value. • Timeticks : counting the time since some epoch in second (relative timer to some event such as startup or reinitialization) • opaque : supporting the capability to pass arbitrary data : specifying octets of binary information, no limit to maximum number of octets : encoded as OCTET STRING

  8. Macro object definition • Object : having a type (syntactic description) and value • To extend ASN.1 to define new types and their values • Macro definition : specifying the syntax of a set of related types • Macro instance : an instance generated from a specific macro definition • Macro instance value : representing a specific entity with a specific value • Macro used for the SNMP MIBs : RFC1155 for MIB-I, RC 1212 (concise MIB definitions) for MIB-II (Fig. 5.3)

  9. MIB Object Definition Format • SYNTAX : ASN.1 syntax for object’s abstract data structure • ACCESS : defining the way in which an instance of the object may be accessed, via SNMP or another protocol - read-only or read-write or write-only or not-accessible • STATUS : current implementation status - mandatory or optional, or deprecated or obsolete • DescrPart : a textual description of the semantics of the object type (optional) • ReferPart : a textual cross-reference to an object defined in some other MIB module (optional) • IndexPart : used in defining tables • DefValPart : defining an acceptable default value that may be used when an object instance is created (optional)

  10. MIB Object Definition Format • OBJECT-TYPE macro (see Fig. 5.3) • A formal template for defining the objects that will consists MIB • ASN.1 module syntax (refer Fig. 5.4) • module : containing specific RFC • Structure of Management Information (RFC 1155, see Fig. 5.4) • An Example of an Object Type Definition (Figure 5.5) << module>> DEFINITIONS :: = BEGIN <<linkage>> <<declarations>> END

  11. Defining Tables • The SMI supports only one form of structuring of data: a simple two-dimensional table with scalar-valued entries. • Definition of tables involves the use of the sequence and sequence-of ASN.1 types and the IndexPart of the OBJECT-TYPE macro. • Object type tcpConnTable (Figure 5.7) (See APPENDIX 5A) • consisting of a SEQUENCE OF TcpConnEntry • each row consists of a SEQUENCE • MIB specification of TCP connection table (RFC 1213) • See Figure 5.6 • The overall table consists of a SEQUENCE OF TcpConnEntry • Each row consists of a SEQUENCE that includes five scalar elements

  12. TCP Entity State Summary

  13. Server Client Unusual Input / Output TCP Entity State Summary (cont’d) Now connection is closed in one direction.

  14. Defining Tables • The entire table represents a single instance of the object type tcpConnTable. • Each row is an instance of the object type tcpConnEntry.

  15. Private MIBs • MIB has been designed to accommodate growth and to provide flexibility for adding new objects. • Private extensions can be added to the private subtree (Figure 5.1) • The management station must be loaded with the private MIB structure • The potential for difficulty arises when the two are from different vendors • Most vendors supply both a text version and a formal description of their MIB extensions • But, vendors can use different formats as follows - The original SNMP SMI specification, RFC 1155 - The newer Concise MIB Format, RFC 1212 - The OSI SMI specification

  16. SNMP V2 • SNMPv2 • Additional types • Integer32 • Counter32 • Gauge32 • Unsigned32 • Counter64

  17. SNMP Overview • RFC 1156 • allow for expansion of the MIB for vendor specific enhancement • RFC 1158 • propose a second MIB (MIB-II) • extend the information base defined in MIB-I • Note: most network devices have software agent that support MIB-II and their own private extensions • Each MIB would focus on a specific technology • RFC 1743: IEEE 802.5 Token Ring Interface type MIB • RFC 1757: Remote Network Monitoring MIB (RMON) • RFC 1513: FDDI Interface type MIB • RFC 1493: Bridge MIB

  18. SNMP Overview • Object Identifier • ISO ASN.1 (Abstract Syntax Notation One) Syntax • a subset of ASN.1 defines the syntax for the MIB • use the tree architecture to organize all available information • labeled node • object identifier (OID) and sort text description Root Node (1) Node (2) Subtree Node (1) Node (2) Node A (1) Object (2) Object (1) OID: 1.2.1.1 or {node A 1} Object A (1)

  19. SNMP Overview • Traversal of the MIB tree • root node • itu-t (0), administered by the ITU-T • iso (1), administered by the ISO • joint-iso-itu-t (2), jointly administered by ISO and ITU-T • internet: OID= 1.3.6.1 or {iso org(3) dod(6), 1} ITU-T(0) ISO(1) joint-ISO-ITU-T (2) …. org(3) ….. ….. dod(6) ….. ….. internet (1) ….. directory(1) …… mgmt(2) …. Experimental(3) private(4) mib(1) enterprises(1)

  20. SNMP Overview • directory (1) • reserved for future use • mgmt(2) • MIB-I originally assigned OID 1.3.6.1.2.1 or {mib 1} • MIB-I has been superseded by MIB-II • system(1): network device operating system • interfaces(2): network interface specific • address translation(3): address mappings • ip(4): Internet protocol specific • icmp(5): ICMP specific • tcp(6): transmission protocol specific • udp(7): user datagram protocol specific • egp(8): exterior gateway protocol specific • cmot(9): CMIP on TCP specific • transmission(10): transmission media specific • snmp(11): SNMP specific

  21. SNMP Overview • experimental (3) • experimental protocols and MIB development intended to enter the standards track • private(4) • used to specify objects defined unilaterally • enterprises(1) or {private 1} • an organization that has registered its own specific extensions to the MIB • vendor-specific MIBs are found • OID (1.3.6.1.4.1) • OIDs represent each manageable object with a unique sequence of numbers and names • SNMP uses the number as an abbreviated form of the name • to make requests for data values • to identify each response that carries the values

  22. Data Network Managing host MS-DOS Router station agent agent Host agent Terminal server agent Device agent SNMP Overview • The five SNMPv1message types (RFC1157) • Get-Request: retrieve information from device • Get-Response: agent responds to the Get-Request • Get-Next-Request: ask for the next specific object • Set-Request: for remote configuration parameter • Trap: an unsolicited message

  23. SNMP Overview • Format of SNMP PDU type Request ID Community 0 Name X Version 0 Value X …….. Get-Request, Get-Next-Request, Set-Request PDU type Request ID Error index Error status ……... Community Version Name X Value X Get-Response PDU type Agent addr Generic trap Specific trap Version Community Enterprise Time Name X Value X Trap SNMP Layer 7 ISO presentation Layer 6 Layer 5 ISO session Layer 4 UDP IP Layer 3 ISO data link Layer 2 Physical Layer 1

  24. SNMP Overview • SNMP trap • an unsolicited message an agent sends to a station • inform the server about the occurrence of specific event • seven types of SNMP traps (MIB-II) • coldstart of a system: reinitialing itself such that its configuration or protocol has changed • warmstart of a system: reinitialing itself such that its configuration or protocol has not changed • link down: a specific link has failed Data Network station Device Managing host agent Link failure Trap: interface #2, link down

  25. SNMP Overview • link up: a specific link has come up • failure of authentication: a request does not provide proper authentication • EGP (Exterior Gateway Protocol) neighbor loss • EGP is a reachability protocol used between data networks • enterprise specific • a vendor to provide additional functionality that complements the generic traps • security • community string • station sends a particular password with each message • the password is referred to as the SNMP community string

  26. station Device Community string: blee Managing host agent SNMP Get, community string = blee Communication string validated, SNMP Get-Response Community string: blee Data Network station Device Managing host agent SNMP Set, community string= public SNMP Trap, authentication failure SNMP Overview • Examples of an SNMP query

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