Configuring SNMP

This chapter 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 3000 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 3000 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. A trap is an asynchronous, unacknowledged message sent from the agent to the SNMP managers listed in the host receiver table. Informs are asynchronous messages sent from the SNMP agent to the SNMP manager which the manager must acknowledge receipt of.

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 3000 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.

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 Chaning (CBC) DES (DES-56) standard.

User-Based Security Model

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.

  • If you create or delete a user using either SNMP or the CLI, the user is created or deleted for both SNMP and the CLI.

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

  • Role changes (deletions or modifications from the CLI are synchronized to SNMP.


Note

When you configure passphrase/password in localized key/encrypted format, Cisco NX-OS does not synchronize the user information (passwords, rules, etc.).

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.

Licensing Requirements for SNMP

This feature does not require a license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.

Guidelines and Limitations for SNMP

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

For more information about supported MIBs, see the following URL:

http:/​/​www.cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml

Default SNMP Settings

Table 2  Default SNMP Parameters

Parameters

Default

license notifications

enabled

linkUp/Down notification type

ietf-extended

Configuring SNMP

Configuring SNMP Users


Note

The commands used to configure SNMP users in Cisco NX-OS are different from those used to configure users in Cisco IOS.

Procedure
     Command or ActionPurpose
    Step 1configure terminal


    Example: 
    switch# configure terminal
switch(config)#
     

    Enters global configuration mode.

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

    Example:
    switch(config)# snmp-server user Admin auth sha abcd1234 priv abcdefgh
     

    Configures an SNMP user with authentication and privacy parameters.

    The passphrase can be any case-sensitive alphanumeric string up to 64 characters.

    If you use the localizedkey keyword, the passphrase can be any case-sensitive alphanumeric string up to 130 characters.

    The engineID format is a 12-digit, colon-separated decimal number.

     
    Step 3switch# show snmp user

    Example:
    switch(config) # show snmp user
          		(Optional)

    Displays information about one or more SNMP users.

     
    Step 4copy running-config startup-config


    Example: 
    switch(config)# copy running-config startup-config
          		(Optional)

    Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration.

     

    The following example configures an SNMP user:

    switch# config t
Enter configuration commands, one per line. End with CNTL/Z.
switch(config)# snmp-server user Admin auth sha abcd1234 priv abcdefgh

    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 security level parameter of either noAuthNoPriv or authNoPriv.

    Use the following command in global configuration mode to enforce SNMP message encryption for a specific user.

    Command

    Purpose

    switch(config)# snmp-server user name enforcePriv

    Enforces SNMP message encryption for this user.

    Use the following command in global configuration mode to 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.

    Filtering SNMP Requests

    You can assign an access list (ACL) to a community to filter incoming SNMP requests. If the assigned ACL allows the incoming request packet, SNMP processes the request. If the ACL denies the request, SNMP drops the request and sends a system message.

    Create the ACL with the following parameters:

    • Source IP address

    • Destination IP address

    • Source port

    • Destination port

    • Protocol (UDP or TCP)

    The ACL applies to both IPv4 and IPv6 over UDP and TCP. After creating the ACL, assign the ACL to the SNMP community.


    Tip

    For more information on creating ACLs, see the NX-OS Security Configuration Guide for the Cisco Nexus Series software that you are using. The security configuration guides available for Nexus 3000 can be found here: http:/​/​www.cisco.com/​en/​US/​products/​ps11541/​products_​installation_​and_​configuration_​guides_​list.html.

    Use the following command in global configuration mode to assign an ACL to a community to filter SNMP requests:

    Command

    Purpose

    switch(config)# snmp-server community community name use-acl acl-name
    Example:
switch(config)# snmp-server community public
use-acl my_acl_for_public

    Assigns an ACL to an SNMP community to filter SNMP requests.

    Before You Begin

    Create an ACL to assign to the SNMP community.

    Assign the ACL to the SNMP community.

    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 ip-address can be an IPv4 or IPv6 address. 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 ip-address can be an IPv4 or IPv6 address. 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 ip-address can be an IPv4 or IPv6 address. 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 3000 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 SNMP for Inband Access

    You can configure SNMP for inband access using the following:

    • Using SNMP v2 without context—You can use a community which is mapped to a context. In this case the SNMP client does not need to know about the context.

    • Using SNMP v2 with context—The SNMP client needs to specify the context by specifying a community, for example, <community>@<context>.

    • Using SNMP v3—You can specify the context.

    Procedure
       Command or ActionPurpose
      Step 1switch# configuration terminal  

      Enters global configuration mode.

       
      Step 2 switch(config)# snmp-server context context-name vrf vrf-name  

      Maps an SNMP context to the management VRF or default VRF. Custom VRFs are not supported.

      The names can be any alphanumeric string up to 32 characters.

       
      Step 3switch(config)# snmp-server community community-name group group-name  

      Maps an SNMPv2c community to an SNMP context and identifies the group that the community belongs. The names can be any alphanumeric string up to 32 characters.

       
      Step 4 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.

       

      The following SNMPv2 example shows how to map a community named snmpdefault to a context:

      switch# config t
Enter configuration commands, one per line.  End with CNTL/Z.
switch(config)# snmp-server context def vrf default
switch(config)# snmp-server community snmpdefault group network-admin
switch(config)# snmp-server mib community-map snmpdefault context def
switch(config)#

      The following SNMPv2 example shows how to configure and inband access to the community comm which is not mapped: 

      switch# config t
Enter configuration commands, one per line.  End with CNTL/Z.
switch(config)# snmp-server context def vrf default
switch(config)# snmp-server community comm group network-admin
switch(config)#

      The following SNMPv3 example shows how to use a v3 username and password: 

      switch# config t
Enter configuration commands, one per line.  End with CNTL/Z.
switch(config)# snmp-server context def vrf default
switch(config)#

      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 3  Enabling SNMP Notifications

      MIB

      Related Commands

      All notifications

      snmp-server enable traps

      BRIDGE-MIB

      snmp-server enable traps bridge newroot

      snmp-server enable traps bridge topologychange

      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.

      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 1configure terminal


        Example: 
        switch# configure terminal
switch(config)#
         

        Enters global configuration mode.

         
        Step 2snmp-server enable traps link [cisco] [ietf | ietf-extended]


        Example:
        switch(config)# snmp-server enable traps link cisco
         

        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.

               

              Disabling SNMP

              Procedure
                 Command or ActionPurpose
                Step 1configure terminal


                Example: 
                switch# configure terminal
switch(config)#
                 

                Enters global configuration mode.

                 
                Step 2 switch(config) # no snmp-server protocol enable

                Example:
                no snmp-server protocol enable
                 

                Disables SNMP.

                SNMP is disabled by default.

                 

                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.