Snmpv3

An Introduction of Simple Network Management Protocol www.sriinduit.blogspot.com

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 and 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 ‘important’ event. (Report alarm)

Message flow:
Massager Element Get packet Response packet Assemble Interested object 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 Trap message by specifying a set of conditions
Trap massages provide the basis for automated event monitoring

Introduction
Motivation
SNMP Architecture
SNMP Message Exchanges
Five basic messages
Transport Protocol
Tools use SNMP
Summary
Outline:

Message Information Base:
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)
Manager Agent Management Information Base Relatively small set of commands

Message Information Base: MIB MIB MIB

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 names  each 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 IpAddrEntry

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
Transport Protocol
Tools use SNMP
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 Commands Follow 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 requests 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

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