Cisco Configuring Simple Network Management Protocol User Guide PDF

Prerequisites for SNMP

Configuring Simple Network Management Protocol Prerequisites for SNMP, on page 1 Restrictions for SNMP, on page 3 Information About SNMP, on page 4 How to Configure SNMP, on page 9 SNMP Examples, on page 18 Monitoring SNMP Status, on page 19 Feature History for Simple Network Management Protocol, on page 19 Prerequisites for SNMP Supported SNMP Versions This software release supports the following SNMP versions: • SNMPv1—The Simple Network Management Protocol, a Full Internet Standard, defined in RFC 1157.

• SNMPv2C replaces the Party-based Administrative and Security Framework of SNMPv2Classic with the community-string-based Administrative Framework of SNMPv2C while retaining the bulk retrieval and improved error handling of SNMPv2Classic. It has these features: • SNMPv2—Version 2 of the Simple Network Management Protocol, a Draft Internet Standard, defined in RFCs 1902 through 1907. • SNMPv2C—The community-string-based Administrative Framework for SNMPv2, an Experimental Internet Protocol defined in RFC 1901. • SNMPv3—Version 3 of the SNMP is an interoperable standards-based protocol defined in RFCs 2273 to 2275.

SNMPv3 provides secure access to devices by authenticating and encrypting packets over the network and includes these security features: • Message integrity—Ensures that a packet was not tampered with in transit. • Authentication—Determines that the message is from a valid source. • Encryption—Mixes the contents of a package to prevent it from being read by an unauthorized source. Configuring Simple Network Management Protocol 1

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Prerequisites for SNMP

To select encryption, enter the priv keyword. Note Both SNMPv1 and SNMPv2C use a community-based form of security. The community of managers able to access the agent’s MIB is defined by an IP address access control list and password. SNMPv2C includes a bulk retrieval function and more detailed error message reporting to management stations. The bulk retrieval function retrieves tables and large quantities of information, minimizing the number of round-trips required. The SNMPv2C improved error-handling includes expanded error codes that distinguish different kinds of error conditions; these conditions are reported through a single error code in SNMPv1.

Error return codes in SNMPv2C report the error type. SNMPv3 provides for both security models and security levels. A security model is an authentication strategy set up for a user and the group within which the user resides. A security level is the permitted level of security within a security model. A combination of the security level and the security model determine which security method is used when handling an SNMP packet. Available security models are SNMPv1, SNMPv2C, and SNMPv3. The following table identifies characteristics and compares different combinations of security models and levels: Table 1:

SNMP Security Models and Levels Configuring Simple Network Management Protocol Prerequisites for SNMP Model Level Authentication Encryption Result SNMPv1 noAuthNoPriv Community string No Uses a community string match for authentication. SNMPv2C noAuthNoPriv Community string No Uses a community string match for authentication. SNMPv3 noAuthNoPriv Username No Uses a username match for authentication. SNMPv3 authNoPriv Message Digest 5 (MD5) or Secure Hash Algorithm (SHA) No Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Configuring Simple Network Management Protocol 2

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Restrictions for SNMP

You must configure the SNMP agent to use the SNMP version supported by the management station. Because an agent can communicate with multiple managers, you can configure the software to support communications using SNMPv1, SNMPv2C, or SNMPv3. Restrictions for SNMP • SNMPv1 does not support informs. • SNMPv3 authentication is not supported in the following scenarios: • If there is a change in the switch priority followed by stack reload. • If a device with a lower MAC address is added to the stack, the device will be elected as the active switch if all the switches in the stack have the same priority.

• To avoid SNMPv3 authentication failure, you should manually configure SNMP engineID on the device before SNMPv3 user configuration. With this, the user can manage and administer the device as the user is tied to the engineID. • The backslash "\" character is not permitted in SNMPv3 authentication and privacy credentials. Configuring Simple Network Management Protocol Restrictions for SNMP Model Level Authentication Encryption Result SNMPv3 authPriv MD5 or SHA Data Encryption Standard (DES) or Advanced Encryption Standard (AES) Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Allows specifying the User-based Security Model (USM) with these encryption algorithms:

• DES 56-bit encryption in addition to authentication based on the CBC-DES (DES-56) standard. • 3DES 168-bit encryption • AES 128-bit, 192-bit, or 256-bit encryption Configuring Simple Network Management Protocol 3

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SNMP Manager Functions

• SNMP ENTITY-MIB is not supported for Ethernet management port. Information About SNMP The following sections provide information about SNMP. SNMP Overview SNMP is an application-layer protocol that provides a message format for communication between managers and agents. The SNMP system consists of an SNMP manager, an SNMP agent, and a management information base (MIB). The SNMP manager can be part of a network management system (NMS) such as Cisco Prime Infrastructure. The agent and MIB reside on the device. To configure SNMP on the device, you define the relationship between the manager and the agent.

The SNMP agent contains MIB variables whose values the SNMP manager can request or change. A manager can get a value from an agent or store a value into the agent. The agent gathers data from the MIB, the repository for information about device parameters and network data. The agent can also respond to a manager's requests to get or set data. An agent can send unsolicited traps to the manager. Traps are messages alerting the SNMP manager to a condition on the network. Traps can mean improper user authentication, restarts, link status (up or down), MAC address tracking, closing of a TCP connection, loss of connection to a neighbor, or other significant events.

SNMP Manager Functions The SNMP manager uses information in the MIB to perform the operations described in the following table: Table 2: SNMP Operations 1 With this operation, an SNMP manager does not need to know the exact variable name. A sequential search is performed to find the needed variable from within a table. 2 The get-bulk command only works with SNMPv2 or later. Configuring Simple Network Management Protocol Information About SNMP Operation Description get-request Retrieves a value from a specific variable.

get-next-request Retrieves a value from a variable within a table.1 get-bulk-request2 Retrieves large blocks of data, such as multiple rows in a table, that would otherwise require the transmission of many small blocks of data. get-response Replies to a get-request, get-next-request, and set-request sent by an NMS. set-request Stores a value in a specific variable. trap An unsolicited message sent by an SNMP agent to an SNMP manager when some event has occurred. Configuring Simple Network Management Protocol 4

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