SNMP Management Information Prof Choong Seon HONG Kyung

SNMP Management Information Prof. Choong Seon HONG Kyung Hee University 1

SNMP Management Information q Database contains information about the elements to be managed : MIB q Each resource to be managed is represented by object q MIB : structured collection of such object having the form of tree q 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 (SMIv 2) And Structure of Management Information Version 1 (SMIv 1) : draftperkins-smi-addition-00. txt l The new data types are Integer 64, Unsigned 64, Float, Double, and Disc. Union (discriminated union) Kyung Hee University 2

Defining objects q 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 l l 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)” l describe the syntax and type of information available in the MIB for TCP/IP networks RFC 1066 l l l use the rules of the SMI present the first version of the MIB for TCP/IP known as MIB-I Kyung Hee University 3

Defining objects RFC 1155 (SMI) l l RFC 1065 later was adopted by the IAB as a full standard four primitive data type – INTEGER • 32 bit 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 Kyung Hee University 4

MIB Structure q Leaf objects of the tree to be actual managed objects to represent some resource, activity, or related information q 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 l directory l mgmt ----> mib-1, mib-2 l experimental l private q MIB tree (see fig. 5. 1) Kyung Hee University 5

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

Object Syntax q Application-wide Types APPLICATION class of ASN. 1 consisting of data types that are relevant to a particular application wide data types defined in RFC 1155 l networkaddress : defined using CHOICE construct, ex) IP Address l ipaddress : 32 -bit address using the format specified in IP l l 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 Kyung Hee University 7

Macro object definition q Object : having a type (syntactic description) and value q To extend ASN. 1 to define new types and their values q Macro definition : specifying the syntax of a set of related types q Macro instance : an instance generated from a specific macro definition q Macro instance value : representing a specific entity with a specific value q Macro used for the SNMP MIBs : RFC 1155 for MIB-I, RC 1212 (concise MIB definitions) for MIB-II (Fig. 5. 3) Kyung Hee University 8

MIB Object Definition Format q SYNTAX : ASN. 1 syntax for object’s abstract data structure q 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 writeonly or not-accessible q STATUS : current implementation status - mandatory or optional, or deprecated or obsolete q Descr. Part : a textual description of the semantics of the object type (optional) q Refer. Part : a textual cross-reference to an object defined in some other MIB module (optional) q Index. Part : used in defining tables q Def. Val. Part : defining an acceptable default value that may be used when an object instance is created (optional) Kyung Hee University 9

MIB Object Definition Format q OBJECT-TYPE macro (see Fig. 5. 3) A formal template for defining the objects that will consists MIB q ASN. 1 module syntax (refer Fig. 5. 4) module : containing specific RFC << module>> DEFINITIONS : : = BEGIN <<linkage>> <<declarations>> END q Structure of Management Information (RFC 1155, see Fig. 5. 4) q An Example of an Object Type Definition (Figure 5. 5) Kyung Hee University 10

Defining Tables q The SMI supports only one form of structuring of data: a simple two-dimensional table with scalar-valued entries. q Definition of tables involves the use of the sequence and sequence-of ASN. 1 types and the Index. Part of the OBJECT-TYPE macro. q Object type tcp. Conn. Table (Figure 5. 7) (See APPENDIX 5 A) consisting of a SEQUENCE OF Tcp. Conn. Entry each row consists of a SEQUENCE q MIB specification of TCP connection table (RFC 1213) See Figure 5. 6 The overall table consists of a SEQUENCE OF Tcp. Conn. Entry Each row consists of a SEQUENCE that includes five scalar elements Kyung Hee University 11

TCP Entity State Summary Kyung Hee University 12

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

Defining Tables q The entire table represents a single instance of the object type tcp. Conn. Table. q Each row is an instance of the object type tcp. Conn. Entry. Kyung Hee University 14

Private MIBs q MIB has been designed to accommodate growth and to provide flexibility for adding new objects. q Private extensions can be added to the private subtree (Figure 5. 1) q The management station must be loaded with the private MIB structure q 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 Kyung Hee University 15

SNMP V 2 q SNMPv 2 Additional types l Integer 32 l Counter 32 l Gauge 32 l Unsigned 32 l Counter 64 Kyung Hee University 16

SNMP Overview RFC 1156 l allow for expansion of the MIB for vendor specific enhancement RFC 1158 l propose a second MIB (MIB-II) l extend the information base defined in MIB-I l Note: most network devices have software agent that support MIB-II and their own private extensions Each MIB would focus on a specific technology l RFC 1743: IEEE 802. 5 Token Ring Interface type MIB l RFC 1757: Remote Network Monitoring MIB (RMON) l RFC 1513: FDDI Interface type MIB l RFC 1493: Bridge MIB Kyung Hee University 17

SNMP Overview q Object Identifier ISO ASN. 1 (Abstract Syntax Notation One) Syntax l a subset of ASN. 1 defines the syntax for the MIB l 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) Kyung Hee University Object A (1) OID: 1. 2. 1. 1 or {node A 1} 18

SNMP Overview Traversal of the MIB tree l 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) …. mib(1) Kyung Hee University Experimental(3) private(4) enterprises(1) 19

SNMP Overview l directory (1) – l 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 Kyung Hee University 20

SNMP Overview l experimental (3) – l 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 l 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 Kyung Hee University 21

SNMP Overview The five SNMPv 1 message types (RFC 1157) l Get-Request: retrieve information from device l Get-Response: agent responds to the Get-Request l Get-Next-Request: ask for the next specific object l Set-Request: for remote configuration parameter l Trap: an unsolicited message Data Network Managing host station MS-DOS agent Host Kyung Hee University agent Terminal server Router agent Device 22

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

SNMP Overview SNMP trap l an unsolicited message an agent sends to a station l inform the server about the occurrence of specific event l 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 Managing host station Data Network Device agent Link failure Trap: interface #2, link down Kyung Hee University 24

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 l community string – station sends a particular password with each message – the password is referred to as the SNMP community string Kyung Hee University 25

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