Explain following in detail :- -

(a) Manager (2M)

(b) Management agent (2M)

(c) MIB (4M)

(d) SMI (4M)

(e) ASN. 1 (4M)

(f) BER. (4M)

Marks: 20 M

Year: May 2014

(a) Manager

i. A manager usually a host controls and monitors a set of agents, usually routers.

ii. The manager is a host that runs the SNMP client program.

iii. A manager can retrieve the value of an object defined in an agent.

iv. A manager can store a value in an object defined in an agent.

• Sends requests to agents
• Monitors alarms
• Houses applications
• Provides user interface

(b) Management Agent

i. The agent is a router or host that runs the SNMP server program.

ii. An agent can send an alarm message to the manager.

• Gathers information from objects
• Configures parameters of objects
• Responds to managers’ requests
• Generates alarms and sends them to mangers

(c) Management information base (MIB):

i. MIBs (Management Information Bases), tell what management information exists

•MIB-I: RFC 1156

•MIB-II: RFC 1213

ii. The representation of objects and information that are relevant to their management forms the management information model.

iii. Information on network components is passed between the agent and management processes. The information model specifies the information base to describe managed objects and the relationship between managed objects.

iv. The structure defining the syntax and semantics of management information is specified by Structure of Management Information (SMI). The information base is called the Management Information Base (MIB).

v. The MIB is used by both agent and management processes to store and exchange management information. The MIB associated with an agent is called an agent MIB and the MIB associated with a manager is designated as the manager MIB.

vi. The manager MIB consists of information on all the network components that it manages; whereas the MIB associated with an agent process needs to know only its local information, its MIB view.

vii. For example, a county may have many libraries. Each library has an index of all the books in that location—its MIB view.

viii. However, the central index at the county's main library, which manages all other libraries, has the index of all books in all the county's libraries—global manager MIB view.

ix. The manager has both the management database (MDB) and the MM.

x. The MIB is a virtual database and contains the information necessary for processes to exchange information among themselves.

Thus,

• Information base contains information about objects
• Organized by grouping of related objects
• Defines relationship between objects
• It is NOT a physical database. It is a virtual database that is compiled into management module.

MIB-II:

• MIB-II is the most important management group of SNMP
• Each device (which supports SNMP) supports MIB-II as well
• RFC1213-MIB defined the branch of mib-2’s OIDs
• Defined base on SMIv1
• Mib-2 defined as, iso.org.dod.internet.mgmt.1 and 1.3.6.1.2.1

Network Configuration with data and Information Base

(d) Structure of Management Information (SMI):

Data definition language for MIB objects

SMI (Structure of Management Information) – Rules specifying the format used to define objects managed that the SNMP protocol accesses

• SMIv1: RFC 1155

• SMIv2: RFC 2578

i. SMI, the Structure of Management Information (a rather oddly named component of the network management framework whose name gives no hint of its functionality), is the language used to define the management information residing in a managed-network entity.

ii. Such a definition language is needed to ensure that the syntax and semantics of the network management data are well defined and unambiguous.

iii. The Structure of Management Information defines precisely how managed objects are named and specifies their associated data-types. SMI is based on object definition language called Abstract Syntax Notation One (ASN.1).

iv. The SMI does not define a specific instance of the data in a man-aged-network entity, but rather the language in which such information is specified.

v. SMI protocol is basically used to standardize the different object attributes like object Identifiers, object type and encoding methods for objects.

• Object Identifiers:

i. Each SNMP object has a unique object identifier. SMI permits object identifiers to be either in name form or in number form.

ii. The naming of SNMP managed objects is based on the universally accepted ASN.1 naming scheme, which is hierarchical in nature. An object ID is made up of a series of integers based on the nodes in the tree, separated by dots.

iii. So, the management branch or mgmt., which defines a standard set of Internet management objects, is named as 1.3.6.1.2 or iso.org.dod.internet.mgmt.

SMI tree

• Object Types :

A manages objects type using a subset of ASN.1 data types. ASN.1, in particular, is a machine-independent, OS-independent, language-independent method for describing integers and other data types and rules that state the manner in which each of the data types are to be transmitted over the network.

• Object Encoding Method:

i. A single instance of a managed object is encoded into a string of octets using the Basic Encoding Rules BER).

ii. BER defines how the objects are encoded and decoded so they can be transmitted over a transport medium such as Ethernet. BER uses TLV (Type, Length, and Value) approach to encoding data for transmission.

iii. So, for each data item to be sent, the data type, the length of the data item and then the actual value of the data item are sent, in that order.

(e) ASN.1

i. ASN.1 is more than just syntax. It is a formal language developed for use with application layers for data transfer between systems.

ii. It is also applicable within the system for clearly separating the abstract syntax and the transfer syntax at the presentation layer.

iii. We define abstract syntax as the set of rules used to specify data types and structures for storage of information. Transfer syntax represents the set of rules for communicating information between systems.

v. Thus, abstract syntax would be applicable to the information model and transfer syntax to the communication model. The abstract syntax can be used with any presentation syntax, depending on the medium of presentation.

v. The abstract syntax in ASN.I makes it independent of the lower-layer protocols. The algorithm to convert the textual ASN.I syntax to machine-readable code is called bask encoding rides (BER).

vi. The relationship between ASN.1 and BER parallels that of source code and machine code.

vii. ASN.1 (Abstract Syntax Notation One) Used to define the format of SNMP messages and managed objects (MIB modules) using an unambiguous data description format

• ASN.1 Data Types

Basic Types: Boolean, Integer, Bitstring, Octet string, Null, Object identifier Real, Enumerated, NumericString, PrintableString, IA5String, UTCTime, GeneralizedTime, CharacterString

Constructed Types: (a) CHOICE (b) SEQUENCE, SEQUENCE OF (c) SET, SET OF

• ASN.1 Symbols:

(f) BER:

i. BER (Basic Encoding Rules), used to encode the SNMP messages into a format suitable for transmission across a network.

ii. The encoding rules used to code ASN.1 syntax defined objects. SNMP message is encoded in BER using type, length, and value (TLV).

iii. CCITT X.209 specifies the Basic Encoding Rules

iv. The relationship between ASN.1 and BER parallels that of source code and machine code

v. All SNMP messages are converted / serialized from ASN.1 notation into smaller, binary data (BER)

vi. Encoding Method: SMI uses another standard, Basic Encoding Rules (BER), to encode data to be transmitted over the network. BER specifies that each piece of data be encoded in triplet format: tag, length, and value.

vii.

viii. Tag: The tag is a 1-byte field that defines the type of data. It is composed of three subfields: class (2 bits), format (1 bit), and number (5 bits).

Tag – Class:

The class subfield defines the scope of the data.

Four classes are defined: universal (00), application wide (01), context-specific (10), and private (11).

i. The universal data types are those taken from ASN1 (INTEGER, OCTET STRING, and ObjectIdentifier).

ii. The applicationwide data types are those added by SMI (IPAddress, Counter, Gauge, and TimeTicks).

iii. The five context-specific data types have meanings that may change from one protocol to another.

iv. The private data types are vendor-specific.

Tag - Format and Number:

i. The format subfield indicates whether the data are simple (0) or structured.

ii. The number subfield further divides simple or structured data into subgroups. For example, in the universal class, with simple format, INTEGER has a value of 2, OCTET STRING has a value of 4, and so on.

Tag - Codes for data types:

Table2: Codes for data types:

Length:

i. The length field is 1 or more bytes.

ii. If it is 1 byte, the most significant bit must be 0. The other 7 bits define the length of the data.

iii. If it is more than 1 byte, the most significant bit of the first byte must be 1. The other 7 bits of the first byte define the number of bytes needed to define the length.

Value: The value field codes the value of the data according to the rules defined in BER.