simple network management protocol - 國立中興大學

2016/2/23 SNM NCHU 1

SNMP –Simple Network

Management Protocol

Lecture 1Overview and Concept

Management Components, SMI, and Management Information

(supplementary: Chapter 1 & 2 of tutorial slides)

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Introduction SNMP Simple Network Management Protocol A set of standards for network management Protocol Database structure specification Data objects

A set of standardized tools that Control costs of network management Across various product types End system, bridges, routers,

telecommunications, …

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History of SNMP Development (1/2) In 1989

SNMP was adopted as TCP/IP-based Internet standards In 1991

RMON - Remote network MONitoring Supplement to SNMP to include management of LAN and LAN

devices In 1995

SNMPv2 Functional enhancements to SNMP SNMP on OSI-based networks

RMON2 (rfc 2021) In 1998

SNMPv3 (proposed) Further enhancements Security capability for SNMP

In 2002SNMPv3 Security, VACM (rfc 3415)

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History of SNMP Development (2/2) In 2008

Traffic Measurements and Trace Exchange Formats Context EngineID Discovery

In 2009 Transport Subsystem and Transport Security Model Relating SYSLOG to notification Secure Shell Transport Mode Remote Authentication Dial-In User Service (RADIUS)

Usage In 2010-2011

Expressing SNMP SMI Datatypes in XML Schema Definition Language

Transport layer security (TLS) transport model

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Network Management Requirements (5 MFAs)

Fault Management Detect, isolate, reconfigurate and repair the abnormal network

environment Problem tracking and control

Problem is truly resolved and no new ones are introduced Accounting Management

Track the use of network resources by end user to provide Impropriate usage tracing, charging, statistics

Configuration and Name Management Startup, shutdown, reconfigure network component when

Upgrade, fault recovery or security checks Performance Management

Capacity utilization, throughput, response time, bottleneck Collect information and assess current situation

Security Management Information protection and access control

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Additions to 5 MFAs Cost Management

Separate cost from mechanism Mobility Management

Improve mobile communication, such as handoff, QoS. Co-existence Management

Integration and co-existence with 3G/4G

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Fundamental Axiomof the Management Framework

The impact of adding network management to managed nodes must be minimal, reflecting a lowest common denominator.

1st tenet: If network management is viewed as an essential aspect of an Internet, then it must be universally deployed on the largest possible collection of devices in the network.

2nd tenet: When all else fails, network management must continue to function, if at all possible.

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Network Management System (1) A collection of tools for Network monitoring Network control Diagnostic report

These tools must be integrated Single operator interface with powerful but

user-friendly Minimal amount of separate equipment is

necessary

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Network Management System (2) Architecture of NMS NMA

Operator interface NME

Collect statistics Response to NMA Alert NMA when

environment changing

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Network Management Software Architecture

Presentation SW Unified interface and handle

information overload Network Management SW (SNMP)

NM applications Admin interested tools

Application element Fault, security, accounting

management Primitive and general-purpose NM

functions Generating alarm, summarizing data

Communication SW (UDP) Exchange management information Communication protocol stack

Database SW (MIB) MIB (Management Information

Base) Configuration and behavior Operation parameters

MIB access modules Convert local MIB to standard form

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In that time .. Network environment is simple ICMP is the only way to do network investigation

ping, traceroute, …. As Internet goes popular, three approaches are

proposed: HEMS: High-level Entity Management System

Considered to be the first network management tools SGMP and SNMP

SNMP was an enhanced version of the Simple Gateway Management Protocol

For TCP/IP-based network management standards Supposed to be short-term solution

CMIP over TCP/IP (CMOT) Common Management Information Protocol For ISO-based network management standards Supposed to be long-term solution

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SNMP Architectural Model

Network

網路介面

SNMPUDP

IP網路介面

SNMPUDP

IP網路介面

SNMPUDP

IP

Manager Agent Agent

. . .

ManagementStation Host Router

Network Elements (NEs)

Network Management

Protocol

SNMP

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Default UDP Ports for SNMP

網路介面

SNMPUDP

IP

Manager

ManagementStation

Network Elements (NEs)

網路介面

SNMPUDP

IP

Agent

162 Any 161 Any

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SNMP Architecture (1) 4 key elements Management Station

Serve as the interface between manager and devices Management applications User-friendly interface Translate manager’s requirements into actual monitoring or

control operations Database extracted from MIBs of all managed device

Management Agent Respond to request from management station Change settings in MIB of managed device Asynchronously report abnormal event (Trap)

Management Information Base (MIB) Each resource is represented as an object and MIB is a collection of objects

Network Management Protocol (SNMP) get, set, trap

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SNMP Architecture (2)

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SNMP Architecture (3) SNMP proxy Devices that do not support UDP/IP ex: Bridge, Modem

Devices that do not want to add burden of SNMP agent ex: PC, programmable controller

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Proxy Agent

Proxy agent exists between standard operations and proprietary operations for Administrative firewall – authenticate and authorize

requests

Caching firewall – cache info. to minimize the burden on a busy device

Transport bridging – support a multi-protocol environment

Protocol translation – translate between the device-specific form and the management form

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SNMP Message Information

Message Information Base (MIB) Collection of objects Each object represents certain resource of

managed device Interoperability of MIB Object that represents a particular resource

should be the same cross various system What objects MIB-I and MIB-II

Common representation format SMI (Structure of Management Information)

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SMI (RFC 1155) Set of rules on how managed objects should be

defined. Objects are defined using Abstract Syntax

Notation One (ASN.1) (ITU-T X.208 / ISO 8824) Identify the data type that can be used in MIB and

how resources are represented and named, including MIB structure Syntax and value of each object Encoding of object value

What is SMI for?

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SMI places a limit on the width and depth that an OID may take: At most 128 sub-identifiers Each sub-identifier must be in the range [0, 232- 1]

There are 3 kinds of object types (for SNMP):1. Simple – INTEGER, OBJECT IDENTIFIER, OCTET STRING,

BIT STRING2. Application-wide – IpAddress, Counter32, Gauge32,

TimeTicks, Opaque, Counter64, UInteger32, …3. Simple constructed – row, table

SMI Places Limit on OID

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<row> ::= (combination of different data types) SEQUENCE { <type1>, …,<typeN>}

<table> ::= SEQUENCE OF <row> (must be the same type)

E.g. ipRoutingTable OBJECT-TYPESYNTAX SEQUENCE OF IpRouteEntry…::= {ip 21}

ipRotueEntry OBJECT-TYPESYNTAX IpRouteEntry…INDEX { ipRouteDest }::= {ipRoutingTable 1}

Table Structure

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Simple Types ---INTEGER, BIT STRING, OCTET STRING, OBJECT IDENTIFIER, NULL

Constructed Types ---SEQUENCE, SEQUENCE OF

Tagged Types ---universal, application-wide, context-specific, private-use

Types and Values (in ASN.1)

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Other than Application-wide types, there are newly defined types, termed textual conventions.

Textual convention macro is invoked as NameOfType ::= TEXTUAL_CONVENTION

<<clauses>>SYNTAX TYPE

e.g. DisplayString ::= TEXTUAL-CONVENTIONDISPLAY-HINT “255a”STATUS currentDESCRIPTION “represents textual information …”SYNTAX OCTET STRING (SIZE (o..255))

Textual Conventions

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DisplayString OCTET STRING (SIZE (0..255)) PhysAddress OCTET STRING MacAddress OCTET STRING (SIZE (6)) TruthValue INTEGER { true(1), false(2)} TestAndIncr INTEGER (0..2147483647) AutonomousType - a value which points to an OID InstancePointer OBJECT IDENTIFIER RowStatus INTEGER { active(1), noInService(2),

notReady(3), createAndGo(4), createAndWait(5), destroy(6)} TimeStamp TimeTicks TimeInterval INTEGER (0.. 2147483647) DateAndTime OCTET STRING (SIZE 8 | 11)) Other range refinement, enumeration refinement, size

refinement, and repertoire refinement.

Pre-defined Textual Conventions

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ASN.1 macro is defined using the form:<<macro-name>> MACRO ::= BEGIN

TYPE NOTATION ::=….

VALUE NOTATION ::= value(…)…

END

Once a macro is defined, it can be used as:nameOfValue <<macrto-name>><<clauses>>::= VALUE

Definition of Macros

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OBJECT-TYPE MACRO ::= BEGIN

TYPE NOTATION ::=“SYNTAX” type(Syntax)UnitsPart“MAX-ACCESS” Access“DESCRIPTION” TextReferPart…

VALUE NOTATION ::= value(VALUE ObjectName)UnitsPart ::= “UNITS” Text | empty Status ::= “current” | “deprecated” | “obsolete”ReferPart ::= “REFERENCE” Text | emptyText ::= “”””string””””…

END

An Example of a Macro Definition

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OBJECT-IDENTITY MACRO ::= BEGIN

TYPE NOTATION ::=“STATUS” Status“DESCRIPTION” TextReferPart

VALUE NOTATION ::= value(VALUE OBJECT IDENTIFIER)

Status ::= “current” | “obsolete”ReferPart ::= “REFERENCE” Text | emptyText ::= “”””string””””

END

Note: Other macro definitions ca be found in p103, 106, 118, 134, 179 in the SIMPLE book.

Another Example of a Macro Definition

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nameOfValue MACRO-NAME<<clauses>>::= VALUE

e.g. ifEntry ::= OBJECT-TYPE { SYNTAX IfEntry…INDEX {ifIndex} ::= {ifTable 1}

NameOfType ::= TYPE (defined type)e.g.IpAddress ::= [APPLICATION 0]

IMPLICIT OCTET STRING (SIZE (4))

nameOfValue NameOfType ::= VALUE (defined value)e.g. internet OBJECT-IDENTIFIER ::= {iso 3 6 1}

Types and Values Definitions

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Modules (high level definition)<<module>> DEFINITIONS ::= BEGIN<<linkage>><<declarations>>ENDThree kinds of objects are defined using ASN.1

• macro --- consists entirely of uppercase letters

• type --- starts with an uppercase letter

• value --- starts with a lowercase letter

Or say, three level of definitions: macro definition, macro instance, and macro instance value.

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SMI (RFC1155)RFC1155-SMI DEFINITIONS ::= BEGINEXPORTS -- EVERYTHING

internet, directory, mgmt, experimental, private,enterprises, OBJECT-TYPE, ObjectName, ObjectSyntax, SimpleSyntax,ApplicationSyntax, NetworkAddress, IpAddress, Counter, Gauge, TimeTicks, Opaque;

internet OBJECT IDENTIFIER ::= { iso org(3) dod(6) 1 }directory OBJECT IDENTIFIER ::= { internet 1 }mgmt OBJECT IDENTIFIER ::= { internet 2 }experimental OBJECT IDENTIFIER ::= { internet 3 }private OBJECT IDENTIFIER ::= { internet 4 }enterprises OBJECT IDENTIFIER ::= { private 1 }

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SMI (cont.)OBJECT-TYPE MACRO ::=

BEGINTYPE NOTATION ::=

"SYNTAX" type (TYPE ObjectSyntax)"ACCESS" Access"STATUS" Status

VALUE NOTATION ::= value (VALUE ObjectName)Access ::= "read-only"

| "read-write"| "write-only"| "not-accessible"

Status ::= "mandatory" | "optional"| "obsolete"

END

ASN.1 Macro

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SMI v1 and v2 (RFC 2578) (1)Data Type

V1 V2__________________________

INTEGER Integer32

OCTET STRING (same)

OBJECT INDETIFIER (same)

NULL (same)

SEQUENCE/SEQUENCE OF (same)

IpAddress (same)

NetworkAddress (same)

Gauge Gauge32

TimeTicks (same)

Opaque (same)

Unsigned32, Counter32, Counter64

BITS

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SMI v1 and v2 (FRC 2578) (2)

Object Definition Enhancement

V1 V2__________________________ ACCESS of MAX-ACCESS of “read-only”, read-write”, write-only”, “read-only”, “read-write”, “read-create”,“not-accessible” “not-accessible”, “accessible-for-notify”

STATUS of STATUS of“current”, “obsolete”, “deprecated” “mandatory”, “obsolete”, “optional”

AUGMENTS adding one column to an existing table

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nameOfValue NameOfType ::= VALUE(Note: invocation once a MACRO is defined)

sysDesc OBJECT-TYPESYNTAX DisplayString (SIZE (0..255))ACCESS read-onlySTATUS mandatory

::= { system 1}

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ObjectName ::= OBJECT IDENTIFIER

ObjectSyntax ::=CHOICE {

simple SimpleSyntax,application-wide

ApplicationSyntax}

SimpleSyntax ::=CHOICE {

number INTEGER,string OCTET STRING,object OBJECT IDENTIFIER,empty NULL} }

ApplicationSyntax ::=CHOICE {

address NetworkAddress,counter Counter,gauge Gauge,ticks TimeTicks,arbitrary Opaque}

NetworkAddress ::=CHOICE {

internet IpAddress}IpAddress ::=

[APPLICATION 0]IMPLICIT OCTET STRING (SIZE (4))

Counter ::=[APPLICATION 1]IMPLICIT INTEGER (0..4294967295)

Gauge ::=[APPLICATION 2]IMPLICIT INTEGER (0..4294967295)

TimeTicks ::=[APPLICATION 3]IMPLICIT INTEGER (0..4294967295)

Opaque ::=[APPLICATION 4] IMPLICIT OCTET STRING

END

NameOfType ::= TYPE

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MIB structure Rooted tree The leaves are the actual managed objects Each object has an identifier (OBJECT

IDENTIFIER) Number with dot as delimiter

The internet node iso -> org -> dod -> internet object identifier of internet node: 1.3.6.1

Under internet node directory :OSI X.500 directory mgmt: used for objects defined in IAB (Internet

Activities Board) experimental: used for internet experiments private: unilaterally usage

MIB Structure

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Define additional objects Under mib-2 Under experimental Under enterprises

MIB Tree

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Concise MIB Definition (RFC 1212)OBJECT-TYPE MACRO ::=

BEGINTYPE NOTATION ::=

"SYNTAX" type(ObjectSyntax)"ACCESS" Access"STATUS" StatusDescrPartReferPartIndexPartDefValPart

VALUE NOTATION ::= value (VALUE ObjectName)

Access ::= “read-only”|”read-write” | “write-only” | ”not-accessible”Status ::= “mandatory” | “optional”| ”obslete” | ”deprecated”

DescrPart ::="DESCRIPTION" value (description DisplayString)

| emptyReferPart ::=

"REFERENCE" value (reference DisplayString)| empty

IndexPart ::="INDEX" "{" IndexTypes "}" | empty

IndexTypes ::=IndexType | IndexTypes "," IndexType

IndexType ::=value (indexobject ObjectName) | type (indextype)

DefValPart ::="DEFVAL" "{" value (defvalue ObjectSyntax) "}"

| emptyEND

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Examples: MIB II (RFC 1213)mib-2 OBJECT IDENTIFIER ::= { mgmt 1 }system OBJECT IDENTIFIER ::= { mib-2 1 }interfaces OBJECT IDENTIFIER ::= { mib-2 2 }at OBJECT IDENTIFIER ::= { mib-2 3 }ip OBJECT IDENTIFIER ::= { mib-2 4 }icmp OBJECT IDENTIFIER ::= { mib-2 5 }

tcp OBJECT IDENTIFIER ::= { mib-2 6 }udp OBJECT IDENTIFIER ::= { mib-2 7 }egp OBJECT IDENTIFIER ::= { mib-2 8 }-- cmot OBJECT IDENTIFIER ::= { mib-2 9 }

transmission OBJECT IDENTIFIER ::= { mib-2 10 }snmp OBJECT IDENTIFIER ::= { mib-2 11 }

ifEntry OBJECT-TYPESYNTAX IfEntryACCESS not-accessibleSTATUS mandatoryDESCRIPTION

"An interface entry containing objects at the subnetwork layer and below for a particular interface."

INDEX { ifIndex }::= { ifTable 1 }

ifTable OBJECT-TYPESYNTAX SEQUENCE OF IfEntry

ACCESS not-accessibleSTATUS mandatory

DESCRIPTION"A list of interface entries. The number of entries is givenby the value of ifNumber."

::= { interfaces 2 }

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Identification of Managed Objects

Use Object Identifier (OID)OID = Object Type OID . Instance IdentifierObject Type OID: Each Object type has a unique OID

Instance Identifier: Identify instances of object type

Eg. mib-2.interface.ifTable.ifEntry.ifDescr.2

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Two Kinds of Managed Objects

Type-Specific Objects (scalar objects): sysDescr OBJECT-TYPE

SYNTAX DisplayString (SIZE(0..255))::= {system 1}

OID: mib-2.system.1.0Columnar Objects OID:

mib-2.interface.ifTable.ifEntry.ifDescr.2mib-2.interface.ifTable.ifEntry.ifDescr.6mib-2.interface.ifTable.ifEntry.ifType.2mib-2.interface.ifTable.ifEntry.ifType.6

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Columnar Objects

ifTable OBJECT-TYPESYNTAX SEQUENCE OF IfEntry…::= { interface 2 }

IfEntry ::= SEQUENCE {ifIndex INTEGER,ifDescr

DisplayString,ifType INTEGER,…

}ifEntry OBJECT-TYPE

SYNTAX IfEntry…INDEX {ifIndex }::= { ifTable 1}

ifDescr OBJECT-TYPESYNTAX DisplayString (SIZE(0..255))ACCESS read-onlySTATUS madatory

...::= {ifEntry 2}

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Columnar Objects

ifIndex ifDescr ifType . . .

1 le0 6 . . .

6 llc0 1 . . .

7 lo0 24 . . .

9 le1 6 . . .

.ifTable.ifEntry.1 (1.3.6.1.2.1.2.2.1.1).ifTable.ifEntry.2 (1.3.6.1.2.1.2.2.1.2)

.ifTable.ifEntry.3 (1.3.6.1.2.1.2.2.1.3)

1.3.6.1.2.1.2.2.1.3.71.3.6.1.2.1.2.2.1.2.6

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Index Objects

Integer-valued: a single sub-identifier

String-valued, fixed-length strings: n sub-identifiers, n= length of the string

String-valued, variable-length strings:n+1 sub-identifiers, the first octet is n (= length)

OID-valued: n+1 sub-identifiers, 1st octet indicates the number of levels

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Index in MIB II (snapshot)

ifEntry {ifIndex}atEntry {atNetIfIndex, atNetAddress}ipAddrEntry {ipAdEntAddr }ipRouteEntry {ipRouteDest}ipNetToMediaEntry {ipNetToMediaIfIndex,

ipNetToMediaNetAddress}tcpConnEntry

{tcpConnLocalAddress, tcpConnLocalPort,tcpConnRemoteAddress, tcpConnRemotePort}

udpEntry {udpLocalAddress, udpLocalPort}egpNeighEntry {egpNeighAddr}

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SNMP Message Information –Object Syntax (1)

Definition of object Data type

Application-independent type (UNIVERSAL type) integer, octetstring, null, object identifier, sequence,

sequence of, choice Application-wide types (RFC 1155) Networkaddress -> ipaddress counter (0 ~ 232 -1), increasing only, wrap to 0 gauge (0 ~ 232 -1) timeticks opaque (encoded as OCTET STRING for transmission) threshold

Value ranges Relationships with other objects in MIB

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ANS.1 Abstract Syntax Notation One A formal language developed by CCITT and ISO In SNMP, we use macro to define other types

and to define managed objects. Macro definition (template) Macro instance (particular type) Macro instance value

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SNMP Message Information –Object Syntax (3) OBJECT-TYPE macro

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Example of object definition iso.org.dod.internet.mgmt.mib-2.tcp.tcpMaxConn 1.3.6.1.2.1.6.4

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2-D table (Eg: tcpConnTable (RFC1213)) Two-dimensional array with scalar-valued entries

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iso (1) -> org (3) -> dod (6) -> internet (1) -> mgmt (2) mib-2 (1) -> tcp (6) -> tcpConnTable(13)

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SNMP Message Information –Multiple Indexed Objects (8)

To get the state of the TCP connection: 10.144.18.118:1200 ===> 10.144.14.40:1600

Use snmp_get_req. to get the “tcpConnState” of the tcpConnTable in MIB II.

tcpConnState ==> .1.3.6.1.2.1.6.13.1.1

.1.3.6.1.2.1.6.13.1.1.10.144.18.118.1200.10.144.14.40.1600

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Standard MIBs

Lecture 2Standard Management Groups in

MIB-II(supplementary: Chapter 3 of tutorial slides)

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IETF MIBs

1212 Concise MIB definitions 1213 MIB-II 1316 Character Stream 1317 RS-232-like Hardware 1471 PPP 1513 RMON for Token Ring 1757 RMON 2021 RMON-II .....

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MIB-II Introduction (1)

RFC1213 MIB-I (RFC 1156) MIB-II is a superset of MIB-I

with some additional objects and groups

175 objects

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MIB-II Introduction (2)Object Identifier (OID): Global identifier for a particular object type. An OID consists of a sequence of integers, which

specify the position of the object in the global object identifier tree. root

ccitt iso joint-iso-ccitt

directory

0 1 2

std regauthority

memberbody org

0 1 2 3

dod

internet

6

1 2 3 4mgmt experimental private

MIB II

system1

interface2

at3

IP4

ICMP5

TCP6

UDP7

EGP8

Trans.10

SNMP11

1 1enterprises

1.3.6.1.2.1.2 1.3.6.1.4.1

1.3.6.1.2.1

MIB II

interface

enterprises

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system group (1) 1.3.6.1.2.1 sysServices

1 physical (ex: repeater) 2 datalink/subnetwork (ex: bridge) 3 internet (ex: router) 4 end-to-end (ex: IP hosts) 7 applications (ex: mail relays)

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system group (2)

system OBJECT IDENTIFIER ::= {mib-2 1} sysServices --- summed integer

for instance, a device supports services of layer 1, 2, and 3 has sysServices = 1+2+4=7

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interfaces group (1) interfaces OBJECT IDENTIFIER := {mib-2 2}

1.3.6.1.2.1.2

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interfaces group (2)

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tcp group

tcp OBJECT IDENTIFIER ::= {mib-2 6}

1.3.6.1.2.1.6

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ip group

1.3.6.1.2.1.4 ip OBJECT IDENTIFIER

::= {mib-2 4}

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INTERFACE STATISTICS MIB-IIIP, TCP & UDP STATISTICS MIB-IISNMP STATISTICS MIB-IIHOST JOB COUNTS HOSTHOST FILE SYSTEM INFORMATION HOSTLINK TESTING REPEATER BRIDGENETWORK TRAFFIC STATISTICS REPEATER BRIDGE RMONTABLE WITH ALL MAC ADDRESSES REPEATER RMONSTATISTICS PER HOST REPEATER RMONHISTORICAL STATISTICS RMONSPANNING TREE PERFORMANCE BRIDGEWIDE AREA LINK PERFORMANCE BRIDGETRESHOLDS FOR ANY VARIABLE RMONCONFIGURABLE STATISTICS RMONTRAFFIC MATRIX WITH ALL NODES RMON‘HOST TOP N’ INFORMATION RMONPACKET / PROTOCOL ANALYSIS RMONDISTRIBUTED LOGGING RMON

RELATION BETWEEN MIBs

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Hardware MIBs and Protocol MIBs

Refer to SimpleWeb mib-intro.pdf for deatails Previous introduction is about MIB-II groups, please also

refer to SimpleWeb mib-2.pdf for updated version.

system group => SNMPv2 MIB (RFC 3418)

interfaces group => IF-MIB (RFC 2863)

at group => deprecated

ip & icmp group => IP-MIB (RFC 2011)

tcp group => TCP-MIB (RFC 2012)

udp group => UDP-MIB (RFC 2013)

egp group => OUTDATED

snmp group => SNMPv2MIB (RFC 3418)

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Other MIBs

Refer to SimpleWeb and RFCs for IF MIB, IP MIB, TCP

MIB, UDP, MIB, HR MIB, …

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Simple Network Management Protocol

Lecture 3SNMPv1 (RFC 1157)

SNMPv2 (RFC1441-1452 )(supplementary: Chapter 4 of tutorial slides)

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SNMPv1 Protocol

Supported operations get, set, trap

Simplicity vs. limitations Not able to change the structure of MIB by adding

or deleting object instances Access is provided only to leaf objects Not able to access entire table or row in single action

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SNMPv1 Operations Support

Three general-purpose operations may be performed on scalar objects： Get：A management station retrieves a scalar

object value from a managed station. Set：A management station updates a scalar

object value in a managed station. Trap：A managed station sends an unsolicited

scalar object value to management station

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SNMP Protocol –management relationship

In management environment The management station and managed agent One-to-many relationship One station may manage all or a subset of target

The managed system and management station One-to-may relationship Each managed station controls its local MIB and

must be able to control the use of that MIB

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Three Management Services A managed station controls its own local MIB

and must be able to control the MIB access by a number of management stations Authentication service: The managed station may

wish to limit access to the MIB to authorized management stations.

Access policy: The managed station may wish to give different access privileges to different management stations.

Proxy service: A managed station may act as a proxy to other managed stations.

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MIB Access and SNMP Access Mode

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SNMP Access Policy

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Concept of Community

An SNMP community is A relationship between an SNMP agent and a set

of SNMP managers that defines Authentication, access control and proxy

The managed system establishes one community for each combination of authentication, access control and proxy

Each community has a unique “community name” Management station uses certain community

name in all get and set operations

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Authentication and Access Using Community

Authentication The community name (password)

Access policy Community profile SNMP MIB view A subset of MIB objects

SNMP access mode READ-ONLY, READ-WRITE

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SNMPv1

SNMP Message Version Identifier Community Name Protocol Data Unit

The length of SNMP messages should not exceed 484 octets.

Message ::=SEQUENCE {

version INTEGER {version-1(0)},community OCTET STRING,data ANY

}

Version Community SNMP PDU

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SNMP AuthenticationCommunity

Relationship between an Agent and Managers.Community Name

Used to validate the SNMP messages. SNMP Password. Default ‘Get’ community name: “public”.

Authentication Failure Agent sends “Authentication Failure Trap” to

Manager.

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SNMPv1 PDU PDU ::= SEQUENCE { request-id INTEGER, error-status INTEGER { noError(0), tooBig(1), noSuchName(2), badValue(3), readOnly(4) genErr(5)}, error-index INTEGER, variable-bindings SEQUENCE OF { name ObjectName, value ObjectSyntax } }

GetRquest :GetNextRequest :

GetResponse :SetRequest :

Trap :

[0] PDU[1] PDU[2] PDU[3] PDU[4] Trap-PDU

Five SNMP PDUs:

PDU: Protocol Data Unit

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SNMPv1 PDU (cont.)

PDU type request-id 0 0 variable-bindings

GetRequest, GetNextRequest, SetRequest

PDU type request-id error-status error-index variable-bindingsGetResponse

variable-bindingsname value name value name value. . .

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Trap-PDUTrap-PDU ::= [4]

IMPLICIT SEQUENCE {enterprise OBJECT IDENTIFIER,agent-addr NetworkAddress,generic-trap INTEGER {

coldStart(0),warmStart(1),linkDown(2),linkUp(3),authenticationFailure(4),egpNeighborLoss(5),enterpriseSpecific(6)},

specific-trap INTEGER,time-stamp TimeTicks,variable-bindings VarBindList

}

Enterprise:Type of Object generating trap.

Agent Address:Address of object generating trap.

Generic Trap:Generic trap type.

Specific Trap:Enterprise specific trap.

Time Stamp:Time elapsed between the last initialization of the network entity andthe generation of the trap.

Variable Bindings“Interesting” information

PDU type enterprise agent-addr generic-trap variable-bindingsspecific-traptime-stamp

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How does a Manager do?

Translates Internal Data to

ASN.1 Format

Sends RequestPDU to Agent

Translates ASN.1Package to Internal

Data Format

Received ResponsePDU from Agent

NMApplication

NMApplication

Agent

Agent

Manager

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How does an Agent do?

Received SNMP Request PDU from Manager

Translates ASN.1Structure to

Internal Data

Maps MIB Variables to

Internal Variables

Sends SNMP Response PDU

to Manager

Translates ResponsePDU to ASN.1

Format

Implement SNMP Request to Set orGet MIB Value

FromManager

ToManager

Agent

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Main Loop of Agent (1/2) Agent waits for an incoming datagram in Port 161 Reads the datagram from UDP and notes the

transport address of the sending entity. Increments the QUANTUM to keep track of the

logical request-id being processed by agent De-serializes the datagram into an ASN.1 structure. If

error occurs, log error and discard packet. The ASN.1 structure is translated into SNMP

message. If error occurs, log error and discard packet. Check on VERSION-NUMBER field. If error occurs,

log error and discard packet.

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Main Loop of Agent (2/2)Community name is looked up.

If community is unknown to agent, agent send authentication trap to Manager station in Port 162; log error and discard packet.

Agent loops through list of variables in the request. If no protocol type is found, return a get-response with

error noSuchName and discard package. Once protocol type is found, operation is checked against

community profile. If mismatch, return get-response with error noSuchName or readOnly and discard package.

Otherwise, agent invokes access routine to perform the desired operation.

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Transmission of an SNMP Message

Actions taken by a Transmitter: The PDU is constructed, using the ASN.1

structure defined in RFC 1157. This PDU is then passed to an authentication

service. The authentication service then performs any required transformation for this exchange.

The protocol entity then constructs a message, consisting of a version field, the community name, and the results from the last step.

This new ASN.1 object is then encoded using the BER and passed to the transport service.

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Receipt of an SNMP Message Actions taken by a Receiver: It does a basic syntax-check of the message and discards

the message if it fails to parse. It verifies the version number and discards the message if

there is a mismatch. The protocol entity then passes the user name, the PDU

portion of the message and the source and destination transport addresses to an authentication service. If authentication fails, the authentication service signals the

SNMP protocol entity, witch generates a trap and discards the message.

If authentication succeeds, the authentication service returns aPDU in the form of an ASN.1 object.

The protocol entity does a basic syntax-check of the PDU and using the named community, the appropriate SNMP access policy is selected and the PDU is processed.

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What's New in SNMPv2 No more Trap PDU, 3 New PDUs: getBulkReq, InformReq, SNMPv2-Trap

Added Security 18 Error Status Values (versus 6 in SNMPv1) SNMPv2 SMI / SNMPv2 MIB M-to-M Communications Enhanced Table Operations ...

(details until we talk about SNMPv3)

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OBJECT-TYPE MACRO ::=BEGIN

TYPE NOTATION ::="SYNTAX" SyntaxUnitsPart"MAX-ACCESS" Access"STATUS" Status"DESCRIPTION" TextReferPartIndexPartDefValPart

VALUE NOTATION ::=value(VALUE ObjectName)

Syntax ::= -- Must be one of the following:-- a base type (or its refinement),-- a textual convention (or its refinement),

or-- a BITS pseudo-type

type| "BITS" "{" NamedBits "}"

NamedBits ::= NamedBit| NamedBits "," NamedBit

NamedBit ::= identifier "(" number ")" -- number is nonnegative

UnitsPart ::="UNITS" Text

| empty

Access ::="not-accessible"

| "accessible-for-notify"| "read-only"| "read-write"| "read-create"

Status ::="current"

| "deprecated"| "obsolete"

ReferPart ::="REFERENCE" Text

| empty

IndexPart ::="INDEX" "{" IndexTypes "}"

| "AUGMENTS" "{" Entry "}"| empty

IndexTypes ::=IndexType

| IndexTypes "," IndexTypeIndexType ::=

"IMPLIED" Index| Index

Index ::=-- use the SYNTAX value of the-- correspondent OBJECT-TYPE invocation

value(ObjectName)Entry ::=

-- use the INDEX value of the-- correspondent OBJECT-TYPE invocation

value(ObjectName)

DefValPart ::= "DEFVAL" "{" Defvalue "}"| empty

Defvalue ::= -- must be valid for the type specified in-- SYNTAX clause of same OBJECT-TYPE macrovalue(ObjectSyntax)

| "{" BitsValue "}"

BitsValue ::= BitNames| empty

BitNames ::= BitName| BitNames "," BitName

BitName ::= identifier

-- a character string as defined in section 3.1.1Text ::= value(IA5String)

END

SNMPv2 macro for object definition

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ObjectName ::=OBJECT IDENTIFIER

NotificationName ::=OBJECT IDENTIFIER

-- syntax of objects-- the "base types" defined here are:-- 3 built-in ASN.1 types: INTEGER, OCTET STRING, OBJECT IDENTIFIER-- 8 application-defined types: Integer32, IpAddress, Counter32,-- Gauge32, Unsigned32, TimeTicks, Opaque, and Counter64ObjectSyntax ::=

CHOICE {simple

SimpleSyntax,-- note that SEQUENCEs for conceptual tables and-- rows are not mentioned here...

application-wideApplicationSyntax

}

-- built-in ASN.1 typesSimpleSyntax ::=

CHOICE {-- INTEGERs with a more restrictive range-- may also be usedinteger-value -- includes Integer32

INTEGER (-2147483648..2147483647),-- OCTET STRINGs with a more restrictive size-- may also be usedstring-value

OCTET STRING (SIZE (0..65535)),objectID-value

OBJECT IDENTIFIER}

-- indistinguishable from INTEGER, but never needs more than-- 32-bits for a two's complement representationInteger32 ::=

INTEGER (-2147483648..2147483647)

-- application-wide types

ApplicationSyntax ::=CHOICE {

ipAddress-valueIpAddress,

counter-valueCounter32,

timeticks-valueTimeTicks,

arbitrary-valueOpaque,

big-counter-valueCounter64,

unsigned-integer-value -- includes Gauge32Unsigned32

}

-- in network-byte order-- (this is a tagged type for historical reasons)IpAddress ::=

[APPLICATION 0]IMPLICIT OCTET STRING (SIZE (4))

-- this wrapsCounter32 ::=

[APPLICATION 1]IMPLICIT INTEGER (0..4294967295)

-- this doesn't wrapGauge32 ::=


-- an unsigned 32-bit quantity-- indistinguishable from Gauge32Unsigned32 ::=


Definitions associated with SNMPv2 macro for object definition

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-- hundredths of seconds since an epochTimeTicks ::=


-- for backward-compatibility onlyOpaque ::=

[APPLICATION 4]IMPLICIT OCTET STRING

-- for counters that wrap in less than one hour with only 32 bitsCounter64 ::=

[APPLICATION 6]IMPLICIT INTEGER

(0..18446744073709551615)

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APPENDIX:Abstract Syntax Notation One (ASN.1) ASN.1: ISO/ITU-T Standards: ISO 8824/ITU-T X.208

Abstract Syntax: Use a syntax to define data/data structure

independent of machine-oriented structures and restrictions.

Use in SNMP Define SNMP PDU format Define management information (MIB)

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What are defined using ASN.1

Types: data structures e.g. Counter, Gauge, IpAddess, ...

Values: instances (variables) of a type e.g. sysContact, ifTable, ifSpeed, ...

Macros: used to change the actual grammar of ASN.1 e.g. OBJECT-TYPE, ACCESS, ...

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Modules

Module: A collection of ASN.1 descriptions Module Structure <module name> DEFINITION ::=

BEGIN<module body>END

Example EmptyModule DEFINITION ::=

BEGIN…END

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Tags and Types (1)

Tags Every type defined in ASN.1 is assigned a tag Tag = Class + P/C + Number Class: (Bit 8,7 in BER tag) Universal 0 0 Application 0 1 Context-specific 1 0 Private 1 1

P/C: primitive or constructed ASN.1 type Number: non-negative Integer

BER: Basic Encoding Rules

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Tags and Types (2)Universal Tag ASN.1 Type

1 BOOLEAN2 INTEGER3 BIT STRING4 OCTET STRING5 NULL6 OBJECT IDENTIFIER7 ObjectDescriptor8 EXTERNAL9 REAL10 ENUMERATED12-15 Reserved16 SEQUENCE, SEQUENCE OF17 SET, SET OF

Universal Tag ASN.1 Type18 NumericString19 PrintableString20 TeletexString21 VediotextString22 IA5String23 UTCTime24 GeneralizeTime25 GraphicString26 VisssibleString27 GeneralString28 CharacterString29-... Reserved

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Tags and Types (3) An ASN.1 type is either primitive or constructed If it is a primitive type, it may be sent either in a

primitive form (encoded in a single collection of octets) or in a constructed form (a resulting octet-encoding is sent).

If it is a constructed type, it is always sent in a constructed form. In most cases, SEQUENCE and SEQUENCE OF are two typical constructed types.

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Tags and Types (4) If the length of the encoding is known, it is termed the

definite form. Primitive encoding always uses definite form for primitive types.

If the length isn’t known ahead of time and that the receiving process should look for a special sequence of octets, end-of-contents, to detect the end of value, it is in indefinite form.

2nd way to calculate the length is to make two passes through the data, which could be inefficient.

If the value is less than 128, one octet is used to encode the length. If the length is longer, the msb of the first octet is set to 1, and remaining 7 bits indicates how many octets follow in the length field.

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Values in ASN.1

General format of a value assignment <valuereference> <type> ::= <value>

Examples: BOOLEAN Married ::= BOOLEAN currentStatus Married ::= FALSE

INTEGER Color ::= INTEGER{red (0), blue (1), yellow (2)} defaultColor Color ::= 1 defaultColor Color ::= blue

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Basic Encode Rules (BER) An ASN.1 encoding rule ISO/ITU-T Standards: ISO 8825/ITU-T X.209 Values from any abstract syntax defined using

ASN.1 can be encoded with BER BER uses Tag, Length, Value (TLV) encoding Tag: “identifier”, Length: length of content, Value:

“contents” Each value may itself be made up of one or

more TLV-encoded values

T TL TL V V

V

L

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BER Examples

Example 1 (from simple book) Example 2 (from W. Stallings)

simple network management protocol - 國立中興大學

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