TSIN02 - Internetworking · TSIN02 - Internetworking 8 SNMP at a glance Introduced in 1988 – To...

TSIN02 - Internetworking

© 2004 Image Coding Group, Linköpings Universitet

Lecture 10: SNMP and AAA

Literature:● Forouzan, chapter 23● RFC2881● RFC2905● RFC2903● Diameter next generation's AAA protocol by Håkan Ventura

(handouts)


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Lecture 10: SNMP and AAA

Outline:

● SNMP

● AAA introduction

● AAA in Network Access Servers

● DIAMETER, an AAA compliant protocol


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Network management framework?

● Management Information Base (MIB)● Structure of Management Information (SMI)● SNMP● Security and Administration● ASN1


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Why network management?

Complex systems are difficult to manage. Too much happens in too many places. Information has to be pooled to be possible to overview.

● All large systems need to be managed systematically– Industrial chemical processes– Large organisations– Electrical power system


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Network management

● Device Management– Checking the state of a device– Changing configuration of a device– Activating or turning of a device– Monitoring a software

● Network Management– Properties of the network as a whole


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Examples of managing tasks– Shutting down a network interface on a router– Checking the speed of an Ethernet interface– Monitoring the temperature on a switch, and

sending a warning if it gets too high– Checking the state of a webserver (the software)– Collecting statistics about link usage


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InfrastructureManaged devices contain objects

whose data is gathered into aManagement Information Base

Data

Data Data

Data

Data

DataAgent

Agent

Agent

AgentAgent

Managingentity

NetworkManagementProtocol


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SNMP at a glance

● Introduced in 1988– To meet the need for a standard for managing IP

devices.● Replaced SGMP

– Simple Gateway Management Protocol was used for managing Internet routers

● Latest version is v3


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SNMP parts

● SMI – Structure of Management Information– The language for defining MIB objects

● MIB – Management Information Base– Defines a set of objects, similar to a database

● SNMP– Application program that allows the manager to

retrieve and store object values in agents, and agents to send alarm messages to the manager

● Security– The main addition from v2 to v3


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SMI – Object Attributes

Figure from Forouzan


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SMI Naming– A tree structure is the basis for SNMP naming– Each tree node is described by dot-separated

numbers/names Root

ccitt(0) iso(1) joint(2)

Org(3)

dod(6)

internet(1)

directory(1) mgmt(2) experimental(3) private(4)

mib-2(1)1.3.6.1.2.1

sys(1) if(2) at(3)

iicmp(5) tcp(6) udp(7) egp(8) trans(11) snmp(12)ip(4)

UdpIn Datagrams(1) UdpNo Ports(2) UdpIn Errors(3) UdpOut Datagrams(4) udpTable(5)


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SMI type and syntax

● Managed agents are heterogenous and may represent data in many different ways

● There is a need for a well-defined and machine-independent syntax

● Solution: ASN.1● Simple datatypes are offered (signed and

unsigned integers, strings, etc)● Structured types can be built from simple types


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Abstract Syntax Notation One (ASN.1)

● ISO standard, defines data types in a machine independent way

● Intermediate format for communication between different machines

Data in machine 1,represented in its

internal representation

Encoder

Transmission in abstract,machine independent form

Decoder

Data in machine 2,represented in its

internal representation


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Data Types



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SMI Encoding - BER

● ASN.1 is not enough for transmission, since it makes an abstract definition of data types

● We need a standardized way of encoding data for transmission

● The solution for this is Basic Encoding Rules● Tag-Length-Value


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Encoding Format


Format

0 – Simple1 - Structured

Tag

00 – ASN.101 – SMI extentions10 – context-specific11 – private (vendor specific)


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Length Format



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Examples



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Management Information Base (v2)

● Each agent has its own MIB● The collection of objects that are managed● The objects are sorted into the groups under

1.3.6.1.2.1 (mib-2)● Only leafs in the tree are accessible● The objects are accessed using SNMP

operations● Lots of standard objects; and extended by

vendor specific ones


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MIB-2



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UDP Group



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UDP Variables and Tables



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Indexes for UDP Table



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Lexicographic Ordering



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SNMP Operations



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SNMP PDU Format



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SNMP Message Format



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UDP Ports



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AAA Introduction

● Authentication– Validate user identity.

● Authorization– Check which services the user is allowed access

to.● Accounting

– Store information about use of a service, eg for billing purposes.


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Authentication

● Validate the identity of a user● Used for

– Access control– Authorization decisions– Account records


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Authentication techniques

● Providing some credential that proves a claimed identity– ID– Smart card– SIM – Certificate– Biometrics– Password– Public – Secret Key pair


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Authentication protocol

Example:

If A wants to contact B through the Internet, how can A prove his/her identity?


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Authorization

● Policy– Identity– Current actions– Outside state–

● Allowing access to services to authenticated users


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Accounting

● Tracking the usage of resources for– Billing– Management– Planning– Auditing–


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Protocols for AAA● RADIUS

–

● TACACS

–

● COPS

–

● DIAMETER

–


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Network Access Server

A Network Access Server (NAS) is often the initial entry point to a network.

A NAS is a gateway between the users and a network, supplying one or more ways to connect, eg.:– Dial-up – direct network access (eg. through SLIP or PPP)– asynchronous terminal services (eg. telnet)– tunneling


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DIAMETER

The Diameter Base Protocol is intended to provide an Authentication, Authorization and Accounting framework for applications such as network access and IP mobility.


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DIAMETER FacilitiesThe Diameter Base Protocol provides the following facilities:

● Delivery of attribute value pairs (AVPs)

● Capabilities negotiation

● Error notification

● Extensiability, through addition of new commands and AVPs

● Basic services necessary for applications, such as handling of user sessions or accounting

The Diameter Base Protocol provides the minimum requirements needed for an AAA-protocol, as defined in RFC2989


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DIAMETER FeaturesAll data delivered by the protocol is in the form of an AVP. These

are used by the base protocol to support the following features:

● Transporting of user authentication information, for the purpose of enabling the Diameter server to authenticae the user.

● Transporting of service specific authorization information, between client and servers, allowing the peers to decide whether a user's access should be granted.

● Exchanging resource usage information, which may be used for accounting purposes, capacity planning etc.

● Relaying, proxying and redirecting of diameter messages through a server hierarchy.

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