snmp

Catalyst 6500 Series Switch Soft 78-15381-01 C H A P T E R38 Configuring SNMP This chapter describes how to configure the Simple Network Management Protocol (SNMP) on the Catalyst 6500 series switches. This chapter consists of these sections: • SNMP Terminology, page 38-1 • Understanding How SNMP Works, page 38-4 • Understanding How SNMPv1 and SNMPv2c Work, page 38-5 • Understanding How SNMPv3 Works, page 38-7 • Enabling and Disabling SNMP Processing, page 38-10 • Configuring SNMPv1 and SNMPv2c on the Switch, page 38-11 • SNMPv1 and SNMPv2c Enhancements in Software Release 7.5(1), page 38-12 • Configuring SNMPv3 on the Switch, page 38-16 Note For complete syntax and usage information for the commands used in this chapter, refer to the Catalyst 6500 Series Switch Command Reference publication. SNMP Terminology Table 38-1 lists the terms that are used in SNMP technology. 38-1 ware Configuration Guide—Release 7.6 Chapter 38 Configuring SNMP SNMP Terminology Table 38-1 SNMP Terminology Term Definition authentication The process of ensuring message integrity and protection against message replays, including both data integrity and data origin authentication. authoritative SNMP engine One of the SNMP copies involved in network communication is designated the allowed SNMP engine to protect against message replay, delay, and redirection. The security keys used for authenticating and encrypting SNMPv3 packets are generated as a function of the authoritative SNMP engine’s ID and user passwords. When an SNMP message expects a response (for example, get exact, get next, set request), the receiver of these messages is authoritative. When an SNMP message does not expect a response, the sender is authoritative. community string A text string used to authenticate messages between a management station and an SNMPv1 or SNMPv2c engine. data integrity A condition or state of data in which a message packet has not been altered or destroyed in an unauthorized manner. data origin authentication The ability to verify the identity of a user on whose behalf the message is supposedly sent. This ability protects users against both message capture and replay by a different SNMP engine and against packets received or sent to a particular user that uses an incorrect password or security level. encryption A method of hiding data from an unauthorized user by scrambling the contents of an SNMP packet. group A set of users belonging to a particular security model. A group defines the access rights for all the users belonging to it. Access rights define the SNMP objects that can be read, written to, or created. In addition, the group defines the notifications that a user is allowed to receive. notification host An SNMP entity to which notifications (traps and informs) are to be sent. notify view A view name (not to exceed 64 characters) for each group; the view name defines the list of notifications that can be sent to each user in the group. privacy An encrypted state of the contents of an SNMP packet; in this state the contents are prevented from being disclosed on a network. Encryption is performed with an algorithm called CBC-DES (DES-56). read view A view name (not to exceed 64 characters) for each group; the view name defines the list of object identifiers (OIDs) that can be read by users belonging to the group. 38-2 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP SNMP Terminology security level A type of security algorithm that is performed on each SNMP packet. There are three levels: noauth, auth, and priv. The noauth level authenticates a packet by a string match of the username. The auth level authenticates a packet by using either the HMAC MD5 or SHA algorithms. The priv level authenticates a packet by using either the HMAC MD5 or SHA algorithms and encrypts the packet using the CBC-DES (DES-56) algorithm. security model The security strategy used by the SNMP agent. Currently, Cisco IOS software supports three security models: SNMPv1, SNMPv2c, and SNMPv3. Simple Network Management Protocol (SNMP) A network management protocol that provides a method to monitor and control network devices and to manage configurations, statistics collection, performance, and security. Simple Network Management Protocol Version 2c (SNMPv2c) Second version of SNMP. This protocol supports centralized and distributed network management strategies and includes improvements in the structure of management information (SMI), protocol operations, management architecture, and security. SNMP engine A copy of SNMP that can reside on the local or remote device. SNMP entity Unlike SNMPv1 and SNMPv2c, in SNMPv3 the terms SNMP Agents and SNMP Managers are no longer used. These concepts have been combined and are called an SNMP entity. An SNMP entity is made up of an SNMP engine and SNMP applications. SNMP group A collection of SNMP users that belong to a common SNMP list that defines an access policy, in which object identification numbers (OIDs) are both read-accessible and write-accessible. Users belonging to a particular SNMP group inherit all of these attributes defined by the group. SNMP user A person for which an SNMP management operation is performed. The user is the person on a remote SNMP engine who receives the inform messages. SNMP view A mapping between SNMP objects and the access rights that are available for those objects. An object can have different access rights in each view. Access rights indicate whether the object is accessible by either a community string or a user. write view A view name (not to exceed 64 characters) for each group; the view name defines the list of object identifiers (OIDs) that can be created or modified by the users of the group. Table 38-1 SNMP Terminology (continued) Term Definition 38-3 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Understanding How SNMP Works Understanding How SNMP Works SNMP is an application-layer protocol that facilitates the exchange of management information between network devices. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth. There are three versions of SNMP: • Version 1 (SNMPv1)—This is the initial implementation of SNMP. Refer to RFC 1157 for a full description of functionality. See the “Understanding How SNMPv1 and SNMPv2c Work” section on page 38-5 for more information on SNMPv1. • Version 2 (SNMPv2c)—The second release of SNMP, described in RFC 1902, has additions and enhancements to data types, counter size, and protocol operations. See the “Understanding How SNMPv1 and SNMPv2c Work” section on page 38-5 for more information on SNMPv2. • Version 3 (SNMPv3)—This is the most recent version of SNMP and is fully described in RFC 2571, RFC 2572, RFC 2573, RFC 2574, and RFC 2575. The SNMP functionality on the Catalyst enterprise LAN switches for SNMPv1 and SNMPv2c remain intact; however, SNMPv3 has significant enhancements to administration and security. See the “Understanding How SNMPv3 Works” section on page 38-7 for more information on SNMPv3. Security Models and Levels A security model is an authentication strategy that is set up for a user and the group in which the user resides. A security level is the permitted level of security within a security model. A combination of a security model and a security level determines which security mechanism is employed when handling an SNMP packet. Three security models are available: SNMPv1, SNMPv2c, and SNMPv3. Table 38-2 identifies the combinations of security models and defines the levels for SNMPv1, SNMPv2c, and SNMPv3. Table 38-2 SNMP Security Levels Model Level Authentication Encryption What Happens v1 noAuthNoPriv Community String No Uses a community string match for authentication. v2c noAuthNoPriv Community String No Uses a community string match for authentication. v3 noAuthNoPriv Username No Uses a username match for authentication. v3 authNoPriv MD5 or SHA No Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. v3 authPriv MD5 or SHA DES Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Provides DES 56-bit encryption in addition to authentication based on the CBC-DES (DES-56) standard. 38-4 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Understanding How SNMPv1 and SNMPv2c Work Note the following about SNMPv3 objects: • Each user belongs to a group • A group defines the access policy for a set of users • SNMP objects access an access policy for reading, writing, and creating • A group determines the list of notifications its users can receive • A group also defines the security model and security level for its users SNMP ifindex Persistence Feature The SNMP ifIndex persistence feature is always enabled. With the ifIndex persistence feature, the ifIndex value of the port and VLAN is always retained and used after the following occurrences: • Switch reboot • High-availability switchover • Software upgrade • Module reset • Module removal and insertion of the same type of module For Fast EtherChannel and Gigabit EtherChannel interfaces, the ifIndex value is only retained and used after a high-availability switchover. Understanding How SNMPv1 and SNMPv2c Work The components of SNMPv1 and SNMPv2c network management fall into three categories: • Managed devices (such as a switch) • SNMP agents and MIBs, including Remote Monitoring (RMON) MIBs, which run on managed devices • SNMP network management applications, such as CiscoWorks2000, which communicate with agents to get statistics and alerts from the managed devices. See the “Using CiscoWorks2000” section on page 38-6 for more information on CiscoWorks2000. Note An SNMP management application, together with the computer it runs on, is called a Network Management System (NMS). Using Managed Devices Catalyst 6500 series switches are managed devices that support SNMP network management with the following features: • SNMP traps (see the “Configuring SNMPv1 and SNMPv2c from the CLI” section on page 38-11) • RMON in the supervisor engine software (see Chapter 39, “Configuring RMON”) • RMON and RMON2 on an external SwitchProbe device 38-5 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Understanding How SNMPv1 and SNMPv2c Work Using SNMP Agents and MIBs SNMP network management uses these SNMP agent functions: • Accessing a MIB variable—This function is initiated by the SNMP agent in response to a request from the NMS. The agent retrieves the value of the requested MIB variable and responds to the NMS with that value. • Setting a MIB variable—This function is also initiated by the SNMP agent in response to a message from the NMS. The SNMP agent changes the value of the MIB variable to the value that is requested by the NMS. Note For more information about MIBs, refer to http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml. • SNMP trap—This function is used to notify an NMS that a significant event has occurred at an agent. When a trap condition occurs, the SNMP agent sends an SNMP trap message to any NMSs that are specified as the trap receivers under the following conditions: – When a port or module goes up or down – When temperature limitations are exceeded – When there are spanning tree topology changes – When there are authentication failures – When power supply errors occur • SNMP community strings—SNMP community strings authenticate access to MIB objects and function as embedded passwords: – Read-only—Gives read access to all objects in the MIB except the community strings but does not allow write access – Read-write—Gives read and write access to all objects in the MIB but does not allow access to the community strings – Read-write-all—Gives read and write access to all objects in the MIB including the community strings Note The community string definitions on your NMS must match at least one of the three community string definitions on the switch. Using CiscoWorks2000 CiscoWorks2000 is a family of Web-based and management platform-independent products for managing Cisco enterprise networks and devices. CiscoWorks2000 includes Resource Manager Essentials and CWSI Campus, which allow you to deploy, configure, monitor, manage, and troubleshoot a switched internetwork. For more information, refer to the following publications: • Getting Started With Resource Manager Essentials • Getting Started With CWSI Campus 38-6 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Understanding How SNMPv3 Works Understanding How SNMPv3 Works SNMPv3 contains all the functionality of SNMPv1 and SNMPv2c, but SNMPv3 has significant enhancements to administration and security. SNMPv3 is an interoperable standards-based protocol that provides secure access to devices by authenticating and encrypting packets over the network. The security features that are provided in SNMPv3 are as follows: • Message integrity—Collects data securely without being tampered with or corrupted • Authentication—Determines that the message is from a valid source • Encryption—Scrambles the contents of a packet to prevent it from being seen by an unauthorized source SNMP Entity Unlike SNMPv1 and SNMPv2c, in SNMPv3 the concept of SNMP Agents and SNMP Managers no longer apply. These concepts have been combined into an SNMP entity. An SNMP entity consists of an SNMP engine and SNMP applications. An SNMP engine consists of the following four components: • Dispatcher • Message processing subsystem • Security subsystem • Access control subsystem Figure 38-1 shows an SNMP entity. Dispatcher The dispatcher is a traffic manager that sends and receives messages. After receiving a message, the dispatcher tries to determine the version number of the message and then passes the message to the appropriate message processing model. The dispatcher is also responsible for dispatching protocol data units (PDUs) to applications and for selecting the appropriate transports for sending messages. 38-7 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Understanding How SNMPv3 Works Figure 38-1 SNMP Entity for Traditional SNMP Agents Message Processing Subsystem The message processing subsystem accepts outgoing PDUs from the dispatcher and prepares them for transmission by wrapping them in a message header and returning them to the dispatcher. The message processing subsystem also accepts incoming messages from the dispatcher, processes each message header, and returns the enclosed PDU to the dispatcher. An implementation of the message processing subsystem may support a single message format corresponding to a single version of SNMP (SNMPv1, SNMPv2c, SNMPv3), or it may contain a number of modules, each supporting a different version of SNMP. Security Subsystem The security subsystem authenticates and encrypts messages. Each outgoing message is passed to the security subsystem from the message processing subsystem. Depending on the services required, the security subsystem may encrypt the enclosed PDU and some fields in the message header. In addition, the security subsystem may generate an authentication code and insert it into the message header. After encryption, the message is returned to the message processing subsystem. v1MP v2cMP v3MP UDP IPX Other Message Dispatcher Proxy foward applications MIB Instrumentation Command responder applications Notification originator applications Transport Mapping PDU Dispatcher SNMP Entity SNMP Engine Access Control Subsystem Security Subsystem Message Processing Subsystem Dispatcher View-based access control model User-based security model Other security model Other access control model SNMP Applications 58 56 8 otherMP 38-8 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Understanding How SNMPv3 Works Each incoming message is passed to the security subsystem from the message processing subsystem. If required, the security subsystem checks the authentication code and performs decryption. The processed message is returned to the message processing subsystem. An implementation of the security subsystem may support one or more distinct security models. The only currently defined security model is the user-based security model (USM) for SNMPv3, which is specified in RFC 2274. The USM protects SNMPv3 messages from the following potential security threats: • An authorized user sending a message that gets modified in transit by an unauthorized SNMP entity. • An unauthorized user trying to masquerade as an authorized user. • A user modifying the message stream. • An unauthorized user listening to the message. The USM currently defines the HMAC-MD5-96 and HMAC-SHA-96 as the authentication protocols and CBC-DES as the privacy protocol. SNMPv1 and SNMPv2c security models provide only community names for authentication and no privacy. Access Control Subsystem The access control subsystem determines whether access to a managed object should be allowed. With the view-based access control model (VACM), you can control which users and which operations can have access to which managed objects. Applications SNMPv3 applications refer to internal applications within an SNMP entity. These internal applications can do the following operations: • Generate SNMP messages • Respond to received SNMP messages • Generate and receive notifications • Forward messages between SNMP entities There are currently five types of applications: • Command generators—Generate SNMP commands to collect or set management data. • Command responders—Provide access to management data. For example, processing get, get-next, get-bulk, and set pdus are used in a command responder application. • Notification originators—Initiate Trap or Inform messages. • Notification receivers—Receive and process Trap or Inform messages. • Proxy forwarders—Forward messages between SNMP entities. 38-9 Catalyst 6500 Series Switch Software Configuration Guide—Release 7.6 78-15381-01 Chapter 38 Configuring SNMP Enabling and Disabling SNMP Processing Enabling and Disabling SNMP Processing This section describes how to use the set snmp enable | disable command to enable or disable the processing of SNMP requests to the switch and SNMP traps from the switch. If you set SNMP to enable mode, SNMP requests to the switch are processed and SNMP traps are sent out if there is no conflict with other SNMP configurations on the switch. If you set SNMP to disable mode, SNMP requests are ignored and no SNMP traps are sent out independent of the other SNMP configurations on the switch. In either SNMP mode (enabled or disabled), you can change other SNMP configurations. RMON-related processes are not affected in either mode. To enable SNMP processing from the command-line interface (CLI), perform this task in privileged mode (enable mode is the default): This example shows how to enable SNMP processing: Console> (enable) set snmp enable SNMP enabled. Console> (enable) This example shows how to disable SNMP processing: Console> (enable) set snmp disable SNMP disabled. Console> (enable) This example shows how to verify the SNMP configuration: Console> (enable) show snmp SNMP: Disabled RMON: Disabled Extended RMON Netflow Enabled : None. Memory usage limit for new RMON entries: 85 percent Traps Enab