network protocols handbook.pdf

37Protocols GuideTCP/IP - Application Layer ProtocolsProtocol NameSNMP: Simple Network ManagementProtocolProtocol DescriptionSNMP, an application layer protocol, is the standard protocoldeveloped to manage nodes (servers, workstations, routers,switches and hubs, etc.) on an IP network. SNMP enables networkadministrators to manage network performance, find andsolve network problems, and plan for network growth. Networkmanagement systems learn of problems by receiving traps orchange notices from network devices implementing SNMP.An SNMP managed network consists of three key components:managed devices, agents, and network-management systems(NMSs). A managed device is a network node that contains anSNMP agent and that resides on a managed network. Manageddevices collect and store management information and makethis information available to NMSs using SNMP. Managed devices,sometimes called network elements, can be routers andaccess servers, switches and bridges, hubs, computer hosts, orprinters. An agent is a network management software modulethat resides in a managed device. An agent has local knowledgeof management information and translates that information intoa form compatible with SNMP. An NMS executes applicationsthat monitor and control managed devices. NMSs provide thebulk of the processing and memory resources required for networkmanagement. One or more NMSs must exist on any managednetwork.Currently, there are three versions of SNMP defined: SNMP v1,SNMP v2 and SNMP v3. Both versions 1 and 2 have a numberof features in common, but SNMPv2 offers enhancements, suchas additional protocol operations. SNMP Version 3 (SNMPv3)adds security and remote configuration capabilities to the previousversions. To solve the incompatible issues among differentversions of SNMP, RFC 3584 defines the coexistence strategies.SNMP also includes a group of extensions as defined by RMON,RMON 2, MIB, MIB2, SMI, OIDs, and Enterprise OIDs.Protocol StructureSNMP is an application protocol, which is encapsulated in UDP.The general SNMP message format for all versions is shownbelow:Version Community PDU• Version -- SNMP version number. Both the managerand agent must use the same version of SNMP. Messagescontaining different version numbers are discardedwithout further processing.• Community -- Community name used for authenticatingthe manager before allowing access to theagent.• PDU (Protocol Data Unit) -- The PDU types and formatsfor SNMPv1, v2 and v3 will be explained in thecorresponding sections.Related protocolsSNMPv1, SNMPv2, SNMPv3, UDP, RMON, SMI, OIDsSponsor SourceSNMP is defined by IETF (http://www.ietf.org) with a group ofRFCs shown in the reference links.Referencehttp://www.javvin.com/protocol/rfc1155.pdfStructure and Identification of Management Information for TCP/IP based internetshttp://www.javvin.com/protocol/rfc1156.pdfManagement Information Base Networkhttp://www.javvin.com/protocol/rfc1157.pdfA Simple Network Management Protocolhttp://www.javvin.com/protocol/rfc1441.pdfIntroduction to SNMPv2http://www.javvin.com/protocol/rfc2579.pdfTextual Conventions for SNMPv2http://www.javvin.com/protocol/rfc2580.pdfConformance Statements for SNMPv2http://www.javvin.com/protocol/rfc2578.pdfStructure of Management Information for SNMPv2http://www.javvin.com/protocol/rfc3416.pdfProtocol Operations for SNMPv2http://www.javvin.com/protocol/rfc3417.pdfTransport Mappings for SNMPv2http://www.javvin.com/protocol/rfc3418.pdfManagement Information Base for SNMPv2http://www.javvin.com/protocol/rfc3410.pdfIntroduction and Applicability Statements for Internet StandardManagement Frameworkhttp://www.javvin.com/protocol/rfc3411.pdfArchitecture for Describing SNMP Frameworkshttp://www.javvin.com/protocol/rfc3412.pdfMessage Processing and Dispatching for the SNMPhttp://www.javvin.com/protocol/rfc3413.pdfSNMP Applicationshttp://www.javvin.com/protocol/rfc3414.pdfUser-based Security Model (USM) for SNMPv3http://www.javvin.com/protocol/rfc3415.pdfView-based Access Control Model for the SNMPhttp://www.javvin.com/protocol/rfc3584.pdfCoexistence between SNMP v1, v2 and v3