Configuring SNMP
Download this chapter
Configuring SNMPConfiguring SNMP
 Feedback

Configuring SNMP

This chapter describes the configuration of the Simple Network Management Protocol (SNMP) on Cisco Nexus 5000 Series switches and contains the following sections:

Information About SNMP

The Simple Network Management Protocol (SNMP) is an application-layer protocol that provides a message format for communication between SNMP managers and agents. SNMP provides a standardized framework and a common language used for the monitoring and management of devices in a network.

SNMP Functional Overview

The SNMP framework consists of three parts:


  • An SNMP manager—The system used to control and monitor the activities of network devices using SNMP.

  • An SNMP agent—The software component within the managed device that maintains the data for the device and reports these data, as needed, to managing systems. The Cisco Nexus 5000 Series switch supports the agent and MIB. To enable the SNMP agent, you must define the relationship between the manager and the agent.

  • A managed information base (MIB)—The collection of managed objects on the SNMP agent


Note

Cisco NX-OS does not support SNMP sets for Ethernet MIBs.

The Cisco Nexus 5000 Series switch supports SNMPv1, SNMPv2c and SNMPv3. Both SNMPv1 and SNMPv2c use a community-based form of security. SNMP is defined in RFC 3410 (http://tools.ietf.org/html/rfc3410), RFC 3411 (http://tools.ietf.org/html/rfc3411), RFC 3412 (http://tools.ietf.org/html/rfc3412), RFC 3413 (http://tools.ietf.org/html/rfc3413), RFC 3414 (http://tools.ietf.org/html/rfc3414), RFC 3415 (http://tools.ietf.org/html/rfc3415), RFC 3416 (http://tools.ietf.org/html/rfc3416), RFC 3417 (http://tools.ietf.org/html/rfc3417), RFC 3418 (http://tools.ietf.org/html/rfc3418), and RFC 3584 (http://tools.ietf.org/html/rfc3584).

SNMP Notifications

A key feature of SNMP is the ability to generate notifications from an SNMP agent. These notifications do not require that requests be sent from the SNMP manager. Notifications can indicate improper user authentication, restarts, the closing of a connection, loss of connection to a neighbor router, or other significant events.

Cisco NX-OS generates SNMP notifications as either traps or informs. Traps are less reliable than informs because the SNMP manager does not send any acknowledgment when it receives a trap. The switch cannot determine if the trap was received. An SNMP manager that receives an inform request acknowledges the message with an SNMP response protocol data unit (PDU). If the Cisco Nexus 5000 Series switch never receives a response, it can send the inform request again.

You can configure Cisco NX-OS to send notifications to multiple host receivers.

SNMPv3

SNMPv3 provides secure access to devices by a combination of authenticating and encrypting frames over the network. The security features provided in SNMPv3 are the following:


  • Message integrity—Ensures that a packet has not been tampered with in-transit.

  • Authentication—Determines the message is from a valid source.

  • Encryption—Scrambles the packet contents to prevent it from being seen by unauthorized sources.

SNMPv3 provides for both security models and security levels. A security model is an authentication strategy that is set up for a user and the role 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.

Security Models and Levels for SNMPv1, v2, v3

The security level determines if an SNMP message needs to be protected from disclosure and if the message needs to be authenticated. The various security levels that exist within a security model are as follows:


  • noAuthNoPriv—Security level that does not provide authentication or encryption.

  • authNoPriv—Security level that provides authentication but does not provide encryption.

  • authPriv—Security level that provides both authentication and encryption.

Three security models are available: SNMPv1, SNMPv2c, and SNMPv3. The security model combined with the security level determine the security mechanism applied when the SNMP message is processed.

User-Based Security Model

The following table identifies what the combinations of security models and levels mean.

Table 1  SNMP Security Models and 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

HMAC-MD5 or HMAC-SHA

No

Provides authentication based on the Hash-Based Message Authentication Code (HMAC) Message Digest 5 (MD5) algorithm or the HMAC Secure Hash Algorithm (SHA).

v3

authPriv

HMAC-MD5 or HMAC-SHA

DES

Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Provides Data Encryption Standard (DES) 56-bit encryption in addition to authentication based on the Cipher Block Chaining (CBC) DES (DES-56) standard.

SNMPv3 User-Based Security Model (USM) refers to SNMP message-level security and offers the following services:


  • Message integrity—Ensures that messages have not been altered or destroyed in an unauthorized manner and that data sequences have not been altered to an extent greater than can occur non-maliciously.

  • Message origin authentication—Ensures that the claimed identity of the user on whose behalf received data was originated is confirmed.

  • Message confidentiality—Ensures that information is not made available or disclosed to unauthorized individuals, entities, or processes.

SNMPv3 authorizes management operations only by configured users and encrypts SNMP messages.

Cisco NX-OS uses two authentication protocols for SNMPv3:


  • HMAC-MD5-96 authentication protocol

  • HMAC-SHA-96 authentication protocol

Cisco NX-OS uses Advanced Encryption Standard (AES) as one of the privacy protocols for SNMPv3 message encryption and conforms with RFC 3826.

The priv option offers a choice of DES or 128-bit AES encryption for SNMP security encryption. The priv option along with the aes-128 token indicates that this privacy password is for generating a 128-bit AES key.The AES priv password can have a minimum of eight characters. If the passphrases are specified in clear text, you can specify a maximum of 64 characters. If you use the localized key, you can specify a maximum of 130 characters.


Note

For an SNMPv3 operation using the external AAA server, you must use AES for the privacy protocol in user configuration on the external AAA server.

CLI and SNMP User Synchronization

SNMPv3 user management can be centralized at the Access Authentication and Accounting (AAA) server level. This centralized user management allows the SNMP agent in Cisco NX-OS to leverage the user authentication service of the AAA server. Once user authentication is verified, the SNMP PDUs are processed further. Additionally, the AAA server is also used to store user group names. SNMP uses the group names to apply the access/role policy that is locally available in the switch.

Any configuration changes made to the user group, role, or password results in database synchronization for both SNMP and AAA.

Cisco NX-OS synchronizes user configuration in the following ways:


  • The auth passphrase specified in the snmp-server user command becomes the password for the CLI user.

  • The password specified in the username command becomes as the auth and priv passphrases for the SNMP user.

  • Deleting a user using either SNMP or the CLI results in the user being deleted for both SNMP and the CLI.

  • User-role mapping changes are synchronized in SNMP and the CLI.


Note

When you configure passphrase/password in localized key/encrypted format, Cisco NX-OS does not synchronize the password.

Group-Based SNMP Access


Note

Because group is a standard SNMP term used industry-wide, roles are referred to as groups in this SNMP section.

SNMP access rights are organized by groups. Each group in SNMP is similar to a role through the CLI. Each group is defined with three accesses: read access, write access, and notification access. Each access can be enabled or disabled within each group.

You can begin communicating with the agent once your user name is created, your roles are set up by your administrator, and you are added to the roles.

Configuration Guidelines and Limitations

SNMP has the following configuration guidelines and limitations:


  • Cisco NX-OS supports read-only access to Ethernet MIBs.

Configuring SNMP

Configuring SNMP Users

To configure a user for SNMP, perform this task:

Procedure
 Command or ActionPurpose
Step 1 switch# configuration terminal
 

Enters configuration mode.

 
Step 2 switch(config)# snmp-server user name [auth {md5 | sha} passphrase [auto] [priv [aes-128] passphrase] [engineID id] [localizedkey]]
 

Configures an SNMP user with authentication and privacy parameters.

 
Step 3 switch# show snmp user
  		(Optional)

Displays information about one or more SNMP users.

 
Step 4 switch# copy running-config startup-config
  		(Optional)

Saves this configuration change.

 

Enforcing SNMP Message Encryption

You can configure SNMP to require authentication or encryption for incoming requests. By default the SNMP agent accepts SNMPv3 messages without authentication and encryption. When you enforce privacy, Cisco NX-OS responds with an authorization Error for any SNMPv3 PDU request using securityLevel parameter of either noAuthNoPriv or authNoPriv.

You can enforce SNMP message encryption for a specific user.

Command

Purpose

switch(config)# snmp-server user name enforcePriv

Enforces SNMP message encryption for this user.

You can enforce SNMP message encryption for all users.

Command

Purpose

switch(config)# snmp-server globalEnforcePriv

Enforces SNMP message encryption for all users.

Assigning SNMPv3 Users to Multiple Roles

After you configure an SNMP user, you can assign multiple roles for the user.


Note

Only users belonging to a network-admin role can assign roles to other users.

Command

Purpose

switch(config)# snmp-server user name group

Associates this SNMP user with the configured user role.

Creating SNMP Communities

You can create SNMP communities for SNMPv1 or SNMPv2c.

To create an SNMP community string in a global configuration mode, perform this task:

Command

Purpose

switch(config)# snmp-server community name group {ro | rw}

Creates an SNMP community string.

Configuring SNMP Notification Receivers

You can configure Cisco NX-OS to generate SNMP notifications to multiple host receivers.

You can configure a host receiver for SNMPv1 traps in a global configuration mode.

Command

Purpose

switch(config)# snmp-server host ip-address traps version 1 community [udp_port number]

Configures a host receiver for SNMPv1 traps. The community can be any alphanumeric string up to 255 characters. The UDP port number range is from 0 to 65535.

You can configure a host receiver for SNMPv2c traps or informs in a global configuration mode.

Command

Purpose

switch(config)# snmp-server host ip-address {traps | informs} version 2c community [udp_port number]

Configures a host receiver for SNMPv2c traps or informs. The community can be any alphanumeric string up to 255 characters. The UDP port number range is from 0 to 65535.

You can configure a host receiver for SNMPv3 traps or informs in a global configuration mode.

Command

Purpose

switch(config)# snmp-server host ip-address {traps | informs} version 3 {auth | noauth | priv} username [udp_port number]

Configures a host receiver for SNMPv2c traps or informs. The username can be any alphanumeric string up to 255 characters. The UDP port number range is from 0 to 65535.


Note

The SNMP manager must know the user credentials (authKey/PrivKey) based on the SNMP engineID of the Cisco Nexus 5000 Series switch to authenticate and decrypt the SNMPv3 messages.

The following example shows how to configure a host receiver for an SNMPv1 trap: 

switch(config)# snmp-server host 192.0.2.1 traps version 1 public

The following example shows how to configure a host receiver for an SNMPv2 inform: 

switch(config)# snmp-server host 192.0.2.1 informs version 2c public

The following example shows how to configure a host receiver for an SNMPv3 inform: 

switch(config)# snmp-server host 192.0.2.1 informs version 3 auth NMS

Configuring the Notification Target User

You must configure a notification target user on the device to send SNMPv3 inform notifications to a notification host receiver.

The Cisco Nexus 5000 Series switch uses the credentials of the notification target user to encrypt the SNMPv3 inform notification messages to the configured notification host receiver.


Note

For authenticating and decrypting the received INFORM PDU, The notification host receiver should have the same user credentials as configured in the Cisco Nexus 5000 Series switch to authenticate and decrypt the informs.

Command

Purpose

switch(config)# snmp-server user name [auth {md5 | sha} passphrase [auto] [priv [aes-128] passphrase] [engineID id]

Configures the notification target user with the specified engine ID for notification host receiver. The engineID format is a 12-digit colon-separated hexadecimal number.

The following example shows how to configure a notification target user: 

switch(config)# snmp-server user NMS auth sha abcd1234 priv abcdefgh engineID 00:00:00:63:00:01:00:a1:ac:15:10:03

Enabling SNMP Notifications

You can enable or disable notifications. If you do not specify a notification name, Cisco NX-OS enables all notifications.


Note

The snmp-server enable traps CLI command enables both traps and informs, depending on the configured notification host receivers.

The following table lists the CLI commands that enable the notifications for Cisco NX-OS MIBs.

Table 2  Enabling SNMP Notifications

MIB

Related Commands

All notifications

snmp-server enable traps

CISCO-AAA-SERVER-MIB

snmp-server enable traps aaa

ENITY-MIB, CISCO-ENTITY-FRU-CONTROL-MIB, CISCO-ENTITY-SENSOR-MIB

snmp-server enable traps entity

snmp-server enable traps entity fru

CISCO-LICENSE-MGR-MIB

snmp-server enable traps license

IF-MIB

snmp-server enable traps link

CISCO-PSM-MIB

snmp-server enable traps port-security

SNMPv2-MIB

snmp-server enable traps snmp

snmp-server enable traps snmp authentication

CISCO-FCC-MIB

snmp-server enable traps fcc

CISCO-DM-MIB

snmp-server enable traps fcdomain

CISCO-NS-MIB

snmp-server enable traps fcns

CISCO-FCS-MIB

snmp-server enable traps fcs discovery-complete

snmp-server enable traps fcs request-reject

CISCO-FDMI-MIB

snmp-server enable traps fdmi

CISCO-FSPF-MIB

snmp-server enable traps fspf

CISCO-PSM-MIB

snmp-server enable traps port-security

CISCO-RSCN-MIB

snmp-server enable traps rscn

snmp-server enable traps rscn els

snmp-server enable traps rscn ils

CISCO-ZS-MIB

snmp-server enable traps zone

snmp-server enable traps zone default-zone-behavior-change

snmp-server enable traps zone merge-failure

snmp-server enable traps zone merge-success

snmp-server enable traps zone request-reject

snmp-server enable traps zone unsupp-mem


Note

The license notifications are enabled by default. All other notifications are disabled by default.

To enable the specified notification in the global configuration mode, perform one of the following tasks:

Command

Purpose

switch(config)# snmp-server enable traps

Enables all SNMP notifications.

switch(config)# snmp-server enable traps aaa [server-state-change]

Enables the AAA SNMP notifications.

switch(config)# snmp-server enable traps entity [fru]

Enables the ENTITY-MIB SNMP notifications.

switch(config)# snmp-server enable traps license

Enables the license SNMP notification.

switch(config)# snmp-server enable traps port-security

Enables the port security SNMP notifications.

switch(config)# snmp-server enable traps snmp [authentication]

Enables the SNMP agent notifications.

Configuring Link Notifications

You can configure which linkUp/linkDown notifications to enable on a device. You can enable the following types of linkUp/linkDown notifications:


  • Cisco—Cisco NX-OS sends only the Cisco-defined notifications (cieLinkUp, cieLinkDow in CISCO-IF-EXTENSION-MIB.my), if ifLinkUpDownTrapEnable (defined in IF-MIB) is enabled for that interface.

  • IETF—Cisco NX-OS sends only the IETF-defined notifications (linkUp, linkDown in IF-MIB) with only the defined varbinds, if ifLinkUpDownTrapEnable (defined in IF-MIB) is enabled for that interface.

  • IEFT extended—Cisco NX-OS sends only the IETF-defined notifications (linkUp, linkDown defined in IF-MIB), if ifLinkUpDownTrapEnable (defined in IF-MIB) is enabled for that interface. Cisco NX-OS adds additional varbinds specific to Cisco Systems in addition to the varbinds defined in the IF-MIB. This is the default setting.

  • IEFT Cisco—Cisco NX-OS sends the notifications (linkUp, linkDown) defined in IF-MIB and notifications (cieLinkUp, cieLinkDown) defined in CISCO-IF-EXTENSION-MIB.my , if ifLinkUpDownTrapEnable (defined in IF-MIB) is enabled for that interface. Cisco NX-OS sends only the varbinds defined in the linkUp and linkDown notifications.

  • IEFT extended Cisco—Cisco NX-OS sends the notifications (linkUp, linkDown) defined in IF-MIB and notifications (cieLinkUp, cieLinkDown) defined in CISCO-IF-EXTENSION-MIB.my, if ifLinkUpDownTrapEnable (defined in IF-MIB) is enabled for that interface. Cisco NX-OS adds additional varbinds specific to Cisco Systems in addition to the varbinds defined in the IF-MIB for the linkUp and linkDown notifications.

Procedure
 Command or ActionPurpose
Step 1switch# configure terminal
 

Enters configuration mode.

 
Step 2switch(config)# snmp-server enable traps link [cisco] [ietf | ietf-extended]
 

Enables the link SNMP notifications.

 

Disabling Link Notifications on an Interface

You can disable linkUp and linkDown notifications on an individual interface. You can use this limit notifications on flapping interface (an interface that transitions between up and down repeatedly).

Procedure
 Command or ActionPurpose
Step 1switch# configure terminal
 

Enters configuration mode.

 
Step 2 switch(config)# interface type slot/port
 

Specifies the interface to be changed.

 
Step 3switch(config -if)# no snmp trap link-status
 

Disables SNMP link-state traps for the interface. Enabled by default.

 

Enabling One-Time Authentication for SNMP over TCP

You can enable a one-time authentication for SNMP over a TCP session.

Command

Purpose

switch(config)# snmp-server tcp-session [auth]

Enables a one-time authentication for SNMP over a TCP session. Default is disabled.

Assigning SNMP Switch Contact and Location Information

You can assign the switch contact information, which is limited to 32 characters (without spaces), and the switch location.

Procedure
 Command or ActionPurpose
Step 1 switch# configuration terminal
 

Enters configuration mode.

 
Step 2 switch(config)# snmp-server contact name
 

Configures sysContact, the SNMP contact name.

 
Step 3 switch(config)# snmp-server location name
 

Configures sysLocation, the SNMP location.

 
Step 4 switch# show snmp
  		(Optional)

Displays information about one or more destination profiles.

 
Step 5 switch# copy running-config startup-config
  		(Optional)

Saves this configuration change.

 

Configuring the Context to Network Entity Mapping

You can configure an SNMP context to map to a logical network entity, such as a protocol instance or VRF.

Procedure
 Command or ActionPurpose
Step 1 switch# configuration terminal
 

Enters configuration mode.

 
Step 2 switch(config)# snmp-server context context-name [instance instance-name] [vrf vrf-name] [topology topology-name]
 

Maps an SNMP context to a protocol instance, VRF, or topology. The names can be any alphanumeric string up to 32 characters.

 
Step 3 switch(config)# snmp-server mib community-map community-name context context-name
 

Maps an SNMPv2c community to an SNMP context. The names can be any alphanumeric string up to 32 characters.

 
Step 4 switch(config)# no snmp-server context context-name [instance instance-name] [vrf vrf-name] [topology topology-name]
  		(Optional)

Deletes the mapping between an SNMP context and a protocol instance, VRF, or topology. The names can be any alphanumeric string up to 32 characters.

Note   

Do not enter an instance, VRF, or topology to delete a context mapping. If you use the instance, vrf, or topology keywords, you configure a mapping between the context and a zero-length string.

 

Verifying SNMP Configuration

To display SNMP configuration information, perform one of the following tasks:

Command

Purpose

switch# show snmp

Displays the SNMP status.

switch# show snmp community

Displays the SNMP community strings.

switch# show snmp engineID

Displays the SNMP engineID.

switch# show snmp group

Displays SNMP roles.

switch# show snmp sessions

Displays SNMP sessions.

switch# show snmp trap

Displays the SNMP notifications enabled or disabled.

switch# show snmp user

Displays SNMPv3 users.

Default SNMP Settings

The following table lists the default settings for SNMP parameters.

Table 3  Default SNMP Parameters

Parameters

Default

license notifications

enabled

linkUp/Down notification type

ietf-extended