Simple Network Management Protocol - Internet - Lecture Slides, Slides of Internet and Information Access

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SNMP

Simple Network Management

Protocol

Simple Network Management Protocol

• SNMP is a framework that provides facilities for managing and monitoring network resources on the Internet.
• Components of SNMP:
  • SNMP agents
  • SNMP managers
  • Management Information Bases (MIBs)
  • SNMP protocol itself

SNMP

IP

UDP

SNMP

SNMP ManagerProcess QueriesRepliesTraps

IP

UDP

SNMP

SNMP AgentProcess objectsAccessData

IP Network

Management Station

SNMP messages

Traps

Managed System

MIB

• Interactions in SNMP

MIBS

• A MIB specifies the managed objects
• MIB is a text file that describes managed objects using the syntax of ASN.1 (Abstract Syntax Notation 1)
• ASN.1 is a formal language for describing data and its properties
• In Linux, MIB files are in the directory /usr/share/snmp/mibs - Multiple MIB files - MIB-II (defined in RFC 1213) defines the managed objects of TCP/IP networks

Organization of managed objects

• Managed objects are organized in a tree-like hierarchy and the OIDs reflect the structure of the hierarchy.
• Each OID represents a node in the tree.
• The OID 1.3.6.1.2. ( iso.org.dod.internet.mgmt.m ib-2) is at the top of the hierarchy for all managed objects of the MIB-II.
• Manufacturers of networking equipment can add product specific objects to the hierarchy.

iso(1) org (3) dod (6) internet (1)

mib-2 (1) system (1) (^) at (3) icmp (5) udp (7) snmp (11)

ipForwDatagrams (6)

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

interface (2) ip (4) tcp (6) egp (8) transmiss

. root

Definition of managed objects in a MIB

• Specification of ipForwDatagrams in MIB-II.

ipForwDatagrams OBJECT-TYPE SYNTAX Counter ACCESS read-only STATUS mandatory DESCRIPTION "The number of input datagrams for which this entity was not their final IP destination, as a result of which an attempt was made to find a route to forward them to that final destination. In entities which do not act as IP Gateways, this counter will include only those packets which were Source-Routed via this entity, and the Source- Route option processing was successful." ::= { ip 6 }

SNMP Protocol

• Get-request. Requests the values of one or more objects
• Get-next-request. Requests the value of the next object, according to a lexicographical ordering of OIDs.
• Set-request. A request to modify the value of one or more objects
• Get-response. Sent by SNMP agent in response to a get-request, get-next-request, or set-request message.
• Trap. An SNMP trap is a notification sent by an SNMP agent to an SNMP manager, which is triggered by certain events at the agent.

Traps

• Traps are messages that asynchronously sent by

an agent to a manager

• Traps are triggered by an event
• Defined traps include:
  • linkDown: Even that an interface went donw
  • coldStart - unexpected restart (i.e., system crash)
  • warmStart - soft reboot
  • linkUp - the opposite of linkDown
  • (SNMP) AuthenticationFailure
  • …

Format of SNMP Packets

• SNMPv1 Get/Set messages:

Version Community (^) SNMP PDU

PDU Type Request ID Error Status Object 1, Value 1 Object 2, Value 2

Error Index

...

Cleartext string that is used as a password PDU type, e.g.: 32: SNMPv1 Get 64: SNMPv2 Get

Unique ID to match requests with replies

Sequence of name-value pairs

SNMP Security

• SNMPv1 uses plain text community strings for

authentication as plain text without

encryption

• SNMPv2 was supposed to fix security

problems, but effort de-railed (The “c” in

SNMPv2c stands for “community”).

• SNMPv3 has numerous security features:

• Ensure that a packet has not been tampered with ( integrity ), Docsity.com

Security levels in SNMPv

SNMP has three security levels:

• noAuthNoPriv : Authentication with matching

a user name.

• authNoPriv : Authentication with MD5 or SHA

message digests.

• authPriv: Authentication with MD5 or SHA

message digests, and encryption with DES

encryption