snmpv3

An Introduction of Simple Network Management Protocol

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Introduction SNMP Architecture Goals of Architecture Motivation Five basic messages Message Information Base Transport Protocol Tools use SNMP SNMP advantages/disadvantages Summary

Outline:

Introduction:

The Internet is:

- a world-wide network of networks

Basically use Transmission Control Protocol/Internet Protocol (TCP/IP).

However, bad things always come alone with positive aspects:

Introduction (cont’d):

As an enterprise networks grow in scale, two facts will become painfully evident:

• The network and its associated resources become crucial to the organization; and

• Many things can go wrong, thereby disabling the network or a portion of it, or degrading performance to an unacceptable level.

SNMP is a key Internet Standard

Introduction (cont’d):

Internet Activities Board (IAB) recommends:

SNMP is used to manage nodes

Part of the Transmission Control Protocol/Internet Protocol (TCP/IP)

Enables administrators to manage network performance, find and solve network problems, and plan for growth

Wondering:

How does SNMP work in networks?

Why IAB recommends SNMP?

Are there any SNMP disadvantages?

SNMP Architecture:

Remote Management Paradigm

SNMP Architecture: A managed device (network elements):

A network node --- contains an SNMP agent; resides on a managed network.

Purpose: Collect and store management information and make it available to NMSs using SNMP.

E.g: routers and access servers, switches and bridges, hubs, computer hosts, or printers.

SNMP Architecture:

An agent: A network-management software module that

resides in a managed device.

Has local knowledge of management information

Translates that information into a form compatible with SNMP

SNMP Architecture:

An NMS (Network management station):

Executes applications that monitor and control managed devices.

Provides the bulk of the processing and memory resources required for network management.

SNMP Architecture:

An Example:

Give you a simple example:

Com-

mander

NMS

Agent

Ins-

pector

Element

Fight

Unit

Goals of the Architecture:

The development cost for management agent software necessary to support the protocol is reduced;

Increasing the degree of management function; E.g: supply additional aspects of network operation a

nd management.

Simplified sets of management functions are easily understood.

Motivation:

No details about interaction between the management application and managed element

It’s impossible to create a list of element management operation that remain new technologies.

Two basic commands and allow parameters to specify all the details: Read / Write

In summary, Management information

NMS Agents (In the network elements)

How can a Message be exchanged?

Motivation:

Five basic messages:

Get, GetNext, GetResponse, Set, and Trap; (Next slide)

Communicate between the manager and the agent.


Get and GetNext messages: Manager to request information for a specific variable.

Agent issue a GetResponse message Set message:

Manager request a change be made to the value of a specific variable

Trap message: Agent to spontaneously inform the manager of an ‘im

portant’ event. (Report alarm)


Message flow:

Massager

Element

Get

packet

Response

packet

Assemble

Interestedobject

Find the match information

Assembled Sent


Most of messages (Get, GetNext and Set) are only issued by manager;

Only “Trap” initiated by an agent; Agent software generates traps Traps are asynchronous A manager configures a network element to generate SNMP Tra

p message by specifying a set of conditions Trap massages provide the basis for automated event monitorin

g

Introduction Motivation SNMP Architecture SNMP Message Exchanges Five basic messages Message Information Base Transport Protocol Tools use SNMP SNMP advantages/disadvantages Summary

Outline:

Message Information Base:

Manager

MIB: SNMP separates definition of the communication protocol and encoding from the set of items that can be accessed

MIB to describe the set of items. (variables)

AgentManagement Information Base

Relatively small set of commands


MIB MIBMIB


MIB is organized in a tree structure with individual variables;

A long numeric tag or object identifier (OID) is used to distinguish each variable uniquely in the MIB and in SNMP messages.

Lists the unique object identifier of each managed element in an SNMP network.

Example of MIB variables

MIB Variable Category Meaning

ipDefaultTTL

tcpMaxConn

IP Routing table

ip

ip

Value IP uses in time-to-live field

ipRoutingTable

tcp Maximum TCP connections allowed

ipRoutingTable: Define contents of a routing table entry, allow network management protocols to reference the data for individual entries.


All in all, MIB document define a name for each variable , in order to let variable can be managed

Problem: Number of variables always getting lager, single MIB document could

not collect all of them. Divide the MIB into multiple documents and can change independently.

However, still may creating conflicts. Hierarchical namespace is being used.

An example:

Numeric label: 1.3.6.1.4.1.2682.1.1

Full name of the node with label:

iso.org.dod.internet.private.enterprises.dpsinc.dpsAtarmControl.TMonXM

An example:

Possible to assign authority for nameseach group owns part of the namespace

Would not have conflict with names assigned by other groups

The MIB then serves as a data dictionary or code book that is used to assemble and interpret SNMP messages.


Good thing: Guarantee MIB variable names would not

conflict with other identifiers

Bad things: Naming scheme arises from the length of

variables names


Many items must be managed consist of complex data aggregate that contain multiple values

Solution for complex data aggregate: MIB naming scheme includes a table construct, data aggregate in which all items are the same or an aggregate in items differ.

E.g: A table corresponds to the physical interfaces in a network element


Reality, what is real situation of MIB module is being used:

Here is an example:

Five MIB module sets developed and maintained by five different organizations


That’s a lot!


IETF’s revision speed is slow


Nearly 70% IETF modules only have one revision

Definition using ASN.1

ANS.1 is a formal language;

All MIB variables be defined and referenced by it;

Two features: a notation used in documents for humans read; A compact encoded representation of the same

information used in communication protocols.


Example: A prefix:

iso.org.dod.internet.mgmt.mib.ip.ipAddrTable Numeric equivalent:

1. 3. 6. 1. 2. 1. 4. 20 Using ASN.1 style notation define this IpAddrEntr

y


ipAddrTable ::= SEQUENCE OF IpAddrEntry

IpAddrEntry ::= SEQUENCE { ipAdEntAddr

IpAddress,ipAdEntIfIndex

INTEGER,ipAdEntNetMask

IpAddress,ipAdEntBcastAddr

IpAddress,ipAdEntReasmMaxSize

INTEGER (0..65535) }

1.3.6.1.2.1.4.20.1.3 ipAdEntNetMask

Define ipAddrTable is a 1-dimensional


ASN.1 can used to select an item consists of an IP address. To specify the network mask field in the

IP address table entry corresponding to address 128.10.2.3

The numeric is :

1.3.6.1.2.1.4.20.1.3.128.10.2.3

Introduction Motivation SNMP Architecture SNMP Message Exchanges Five basic messages Message Information Base Transport Protocol Tools use SNMP SNMP advantages/disadvantages Summary

Outline:

Transport Protocol:

SNMP allows the use of either UDP or TCP

Management software can either send message in a separate UDP packet or open a TCP connection.

The software can handles each message independently.

Tools use SNMP:

Provide a high-level interface Hide the details of MIB variables SNMP massages Easy to understand, manager prefer

Provide a low-level interface Manager can form and send a message (commands) Add a new device in network before HL management

tools are installed.

SNMP advantages:

Simple design & implementation users to easily program variables that they

want to monitor

Expansibility Protocol can be updated to meet future needs.

SNMP Disadvantages:

Security gaps Intruders access to the information carried along the

network SNMP version 2 has fixed some security issues

Not a particularly efficient protocol

Bandwidth is wasted with needless information

E.g:SNMP version multiple length

Summary：

Give you a simple example:

Com-

mander

NMS

Agent

Ins-

pector

Element

Fight

Unit

GPS

MIB

Five basic messages

CommandsFollow

messages

Return

Summary:

SNMP is the most popular network management protocol in the TCP/IP protocol suite.

SNMP is a simple request/response protocol that communicates management information between managers and agents.

MIB is used to define the set of variables. Variables are described using ASN.1

References:

[1] J.Case, M.Fedor, “A Simple Network Management Protocol (SNMP)”, RFC 1157, May 1990.

[2] “Simple Network Management Protocol”, Internetworking Technologies Handbook, Chapter 56.

[3] J. Schonwalder, “Characterization of SNMP MIB Modules”, International University Bremen

[4] Comer, D., “Automated Network Management Systems”, Prentice Hall, 2006

[5] “http://nislab.bu.edu/sc546/sc441Spring2003/snmp/howSNMPworks.html” [6] “http://www.wtcs.org/snmp4tpc/snmp.htm”

Thank you !

Any Comments?

The End

Update, Messages, Atomicity

SNMP guarantees that either all Set commands in a given message must succeed or none of them should be performed. E.g: Management software sends Set req

uests to multiple elements:

succeed or fail

SNMP Message Exchanges:

Application entities: entities residing at management stations and network elements communicate with one another

Community: Pairing of an SNMP agent with some arbitrary set of SNMP application entities

E.g: Authentic Messages belong to the community

Elements of the Architecture:

The scope and representation of the management information communicated by the protocol;

Operations on management information supported by the protocol;

The form and meaning of exchanges among management entities;

The definition of administrative relationships among management entities,

The form and meaning of references to management information


Packet structure:

UDP (User Datagram Protocol) is the IP transport layer protocol that supports SNMP messages

snmpv3

Technology

snmp network

snmp agent

snmp messages

snmp trap message

snmp separatesdefinition

snmp work

snmp disadvantages

mib mib mib