Advanced Network Protocols

CSCI 5132Chapter 30

Simple Network Management Protocol

ByChetan SinghHaaris Sheikh

Lakshmi MenonKavita Sarma

Level of Management Protocols

Wide area networks include management protocols as part Of their link level protocols.Control packets are used by the receiver to respond to commends from the manager to handle packet switch misbehaving. The switch can resume normal operation once the problem is fixed. TCP/IP does not have a single link level protocol as the internet consists of multiple physical networks interconnected by IP routers.

Level of Management Protocols (Cont..)

The differences between internet management are: - A single manager can control heterogeneous devices. - The controlled entities may not share common link level protocol. - The manager controls a set of machines that may lie in different physical networks.The internet management protocol used with TCP/IPoperates above the transport level i.e the application level.

Level of Management Protocols (Cont..)Advantages of using the internet management

software in the application layer: - One set of protocols can be used for all networks. - One set of protocols can be used for all managed devices. - Routers can be managed without direct attachment to every physical network or router.Disadvantages: - Routers con not be contacted if either the operating system, IP software or transport software fail.

Architectural Model

Client software runs on the manager’s machine.The management agent(server program) is run on each participating router or host.A manager tells a client about the agent it wants to communicate with.The client sends commands or queries to the agent.The management software uses an authentication mechanism to ensure that only authorized managers can access or controla particular device.

Protocol Framework

TCP/IP management protocols divide the management problem into two parts specifying separate standards for each part.The first part specifies hoe the client communicates with the agent.The second part specifies which data item a managed device must keep.Simple Network Management Protocol (SNMP) is the TCP/IP standard for network management.

Standard For Managed Information

A device being managed must keep control and status information that the manager can access.SNMP allows a manager to access the statistics but does not specify which data can be accessed.Management Information Base (MIB) is a standard that specifies what data items a managed device must keep and the operations allowed on each.MIB divides management information into many categories and the choice of categories are important because identifiers used to specify items include a code for the category.

Examples of MIB Variables

Separate RFC’s exist that specify MIB variables associated with different devices.Also many vendors have specified MIB variables for theirproducts.Refer to Figure 30.3. for a small list of MIB variables.MIB variables present only a logical definition of each data item.The internal data structures a router uses may differ from the MIB definition.

THE STRUCTURE OF MANAGEMENT INFORMATION (SMI)• SMI is a set of rules used to define and

identify MIB variables.• It places restrictions on types of

variables allowed in MIB.• Specifies rules for naming variables.• Creates rules for defining variable

types.

THE STRUCTURE OF MANAGEMENT INFORMATION (SMI)• Example:

– SMI standard includes definitions of terms like:– IPAddress as a 4-octet string,– Counter, an integer in the range of 0 to 223-1.

– Also specifies that these are the terms used to define MIB variables.

• The rules in SMI, most importantly, describe how MIB refers to tables of values (e.g., IP routing table).

FORMAL DEFINITIONS USING ASN.1

• The TCP/IP network mangement protocols use a formal notation called Abstract Syntax Notation (ASN.1) to define names and types for variables in the management information base. The precise notation makes the form and contents of variables unambiguous.

• Precision is important when implementations include hetrogeneous computers that do not all use the same representations for data items.

FORMAL DEFINITIONS USING ASN.1

• Example:– A protocol using ASN.1 must state

exact form and range of numeric values instead of simply specifying that a variable contains an integer value.

• ASN.1 also simplifies the implementation of network management and guarantees interoperability.

STRUCTURE AND REPRESENTATION OF MIB

OBJECT NAMES• Names for MIB variables are taken from the

object identifier namespace administered by ISO & ITU.

• Object Identifier provides a namespace in which all possible objects can be designated. The namespace includes variables used in network management and names for arbitrary objects.

• Object Identifier namespace is absolute(global) and hierarchical (Fig 30.4).

STRUCTURE AND REPRESENTATION OF MIB

OBJECT NAMES• The name of an object in the

hierarchy is a sequence of numeric labels, separated with periods to identify an individual component, on the nodes along a path from the node to the object.

• Example:– The name 1.3.6.1.2 denotes the node

mgmt (Fig 30.4).

STRUCTURE AND REPRESENTATION OF MIB

OBJECT NAMES• MIB groups variables into categories.• The categories are the subtrees of the MIB

node of the object identifier namespace (Fig 30.5).

• Examples:– Refer to Fig 30.5.

• MIB standards do not dictate the implementation, instead provides a uniform and virtual interface to access data.

Simple Network Management Protocol

• Network management protocols specify communication between the network management client and a network management server program that executes at the host or the router

• The protocol needs to be flexible and compatible to changes.

• Does not define a large set of commands.

• Uses the fetch and store paradigm

SNMP contd

• Taking a conceptual view of SNMP it contains only 2 commands

• Example if you want to reboot: Declare a data item that gives the time

until the next reboot and allows the manager to assign a value to the item like 0

Advantages

• Stability Definitions remain fixed even if new items are added.

• Simplicity Saves the complexity of having special cases for each command

• Flexibility Accommodates arbitrary commands in an elegant frame work

SNMP hidden facts!

• Looking at the managers point of view SNMP remains hidden

• SNMP software comes with a GUI interface that displays diagrams of network connectivity and uses the point and click interaction technique

• figure 30.6 in the book shows the fetch and store commands

• Get request – fetch• Set request – store • Response – provides a reply.

SNMP operations

• atomicIf the SNMP message specifies operations on multiple variables the server either performs all operations on all of them or on none of them

• trap Allows managers to program servers

to send information when an event occurs.

Searching table using names

• ASN.1 does not provide mechanisms for declaring arrays or indexing.

• In order to iterate through the table the client can use the get-next-request operation which does the iteration

An Example

• An example search: The client is not aware of the IP addresses

that are currently The client uses the prefix in order to get-next –request

iso.org.dod.internet.mgmt.mib.ip.ipAddrEntry.ipAdEntNetMask

The server then returns the network mask field of the first entry in ipAddrTable .

SNMP Message Format

• SNMP messages do not have fixed fields • They use standard ASN.1 encoding

which is not in human readable form• It consists of a descriptive name followed

by the declaration of the item’s type. msgVersion

INTEGER(0..2147483647)

a non negative number < = 2147483647

SNMP Message formats

• Integer identifies the protocol version

• Header data ref figure 30.8 page 567• Security parameters• Data Area this is divided into PDU –Protocol data

unitsPDU consists of a request and a response from the client and the agent respectively.This also offers a choice of plain text or encrypted text

Notes:technically called discriminated union

SNMP Message contd….• SNMPv3 distinguishes between an

application that uses the service SNMP supplies and an engine that is the underlying software

• The encrypted text PDU begins with a identifier for the engine along with the engine ID.

• data ANY implies that the context field has the exact details of the data.

SNMP Definitions -ERRORS

• Error-status and Error-indexthese are single octet integers which contain the value zero in a request.

• If an error occurs the values in the response identify the cause

• The last parameter VarBindList is a sequence of pairs of object name and value.

Example Encode SNMP Message

• Encoded form of ASN.1 uses variable length fields to represent items.

• Each field begins with a header that specifies the type of object and its length in bytes.

• The msg starts with a code for SEQUENCE which has a length of 103 octets.

• 1st item = 1 octet integer = protocol version.

• Successive fields indicate msg ID and the maximum message size the sender can accept in a reply.

• Security information follows the msg header.

• GetRequest-PDU occupies the tail of the message.

• ScopedPDU specifies a context in which to interpret the remainder of the message.

• Octet A0 specifies the operation as a get-Request.(Since high order bit is turned on the interpretation is context specific).

• The length octet specifies the request is 26 octets long.

• The request ID is 2 octets.• Each of the error-status and error-index

are 1 octet.• Finally, the sequence pairs contains

one binding. A binding is a single object identifier bound to a null value.

• The identifier is encoded. The first two numeric labels are combined into a single octet.

New Features In SNMPv3

• The primary changes are in the areas of security and administration.

• First, SNMPv3 is designed to have both general and flexible security policies.– SNMPv3 includes facilities for several

aspects of security, and allows each to be configured independently.

• Second, the system is designed to make administration of security easy.– V3 allows remote configuration,

meaning that an authorized manager can change the configuration of security items listed above without being physically present at the device.

Summary• Network Management Protocols allow a

manager to monitor and control routers and hosts.

• A network management client program executing on the manager’s workstation contacts one or more servers, called agents, running on the devices to be controlled.

• As an internet consists of heterogeneous machines and networks, TCP/IP management software executes as application programs and uses internet transport protocols for communication.

Summary Contd.• SNMP , the standard TCP/IP network

management protocol defines a low-level management protocol that performs two conceptual operations:– Fetch a value from a variable or store

a value into a variable.• SNMP defines the format of messages

that travel between a manager’s computer and a managed entity.

Summary Contd.• A set of companion standards to SNMP define

the set of variables that a managed entity maintains.

• The set of variables comprise a Management Information Base(MIB) variables described using ASN.1, a formal language that provides a concise encoded form , also human readable notation for names and objects.

• ASN.1 uses a hierarchical namespace to guarantee that all MIB names are globally unique while still allowing subgroups to assign parts of the namespace.

Any Questions?