Cisco Nexus 1000V System Management Configuration Guide, Release 4.2(1)SV2(1.1)
Configuring SNMP
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Configuring SNMP

Contents

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. Cisco Nexus 1000V 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.

SNMP is defined in RFCs 3411 to 3418.


Note


SNMP Role Based Access Control (RBAC) is not supported.


SNMPv1, SNMPv2c, and SNMPv3. Both SNMPv1 and SNMPv2c use a community-based form of security are supported.

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 a connection to a neighbor router, or other significant events.

SNMP notifications are generated 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 Cisco Nexus 1000V 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 1000V never receives a response, it can send the inform request again.

You can configure Cisco Nexus 1000V to send notifications to multiple host receivers. See “Configuring SNMP Notification Receivers” more information about 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 as follows:

  • 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.

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

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.

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 nonmaliciously.
  • 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 Nexus 1000V uses two authentication protocols for SNMPv3:

  • HMAC-MD5-96 authentication protocol
  • HMAC-SHA-96 authentication protocol

The Cisco Nexus 1000V 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 case-sensitive alphanumeric characters. If you use the localized key, you can specify a maximum of 130 characters.


Note


For an SNMPv3 operation that uses the external AAA server, you must use AES for the privacy protocol in the 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 Nexus 1000V 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 Nexus 1000V synchronizes user configuration in the following ways:

  • The authentication 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 authentication and privacy passphrases for the SNMP user.
  • If you delete a user using either SNMP or the CLI, the user is 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 Nexus 1000V does not synchronize the password.


Cisco NX-OS holds the synchronized user configuration for 60 minutes by default. See the Modifying the AAA Synchronization Time section for information on how to modify this default value.

Group-Based SNMP Access


Note


Because group is a standard SNMP term used industry-wide, we refer to role(s) as group(s) 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 read access or read-write access.

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

High Availability

Stateless restarts for SNMP are supported. After a reboot or supervisor switchover, the running configuration is applied.

Guidelines and Limitations for SNMP

  • Read-only access to some SNMP MIBs is supported. See the Cisco NX-OS MIB support list at the following URL for more information: http:/​/​www.cisco.com/​public/​sw-center/​netmgmt/​cmtk/​mibs.shtml
  • SNMP Role Based Access Control (RBAC) is not supported.
  • The SNMP set command is supported by the following Cisco MIBs:
    • CISCO-IMAGE-UPGRADE-MIB
    • CISCO-CONFIG-COPY-MIB
  • The recommended SNMP polling interval time is 5 minutes.

Default Settings for SNMP

Parameters

Default

license notifications

enabled

Configuring SNMP

This section includes the following topics:

  • Configuring SNMP
  • Users Enforcing SNMP Message Encryption
  • Creating SNMP Communities
  • Configuring SNMP Notification Receivers
  • Configuring the Notification Target User
  • Enabling SNMP Notifications
  • Disabling LinkUp/LinkDown Notifications on an Interface
  • Enabling a One-time Authentication for SNMP over TCP
  • Assigning the SNMP Switch Contact and Location Information
  • Disabling SNMP
  • Modifying the AAA Synchronization Time

Configuring SNMP Users

Before You Begin

Before beginning this procedure, you must be logged in to the CLI in EXEC mode.

Procedure
     Command or ActionPurpose
    Step 1switch# configure terminal 

    Places you in global configuration mode.

     
    Step 2switch(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. The passphrase can be any case-sensitive, alphanumeric string up to 64 characters. If you use the localizekey keyword, the passphrase can be any case-sensitive, alphanumeric string up to 130 characters.

    The name argument is the name of a user who can access the SNMP engine.

    The auth keyword enables one-time authentication for SNMP over a TCP session. It is optional.

    The md5 keyword specifies HMAC MD5 algorithm for authentication. It is optional.

    The sha keyword specifies HMAC SHA algorithm for authentication. It is optional.

    The priv keyword specifies encryption parameters for the user. It is optional.

    The aes-128 keyword specifies a 128-byte AES algorithm for privacy. It is optional.

    The engineID keyword specifies the engineID for configuring the notification target user (for V3 informs). It is optional.

    The id is a 12-digit colon-separated decimal number.

     
    Step 3switch(config-callhome)# show snmp user  (Optional)

    Displays information about one or more SNMP users.

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

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

     
    switch# configure terminal
    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 for All Users

    Procedure
       Command or ActionPurpose
      Step 1switch(config)# snmp-server globalEnforcePriv  

      Enforces SNMP message encryption for all users. 

      switch(config)# snmp-server globalEnforcePriv

      Creating SNMP Communities

      You can create SNMP communities for SNMPv1 or SNMPv2c.

      Before You Begin

      You must be in global configuration mode.

      Procedure
         Command or ActionPurpose
        Step 1 switch(config)# snmp-server community name {ro | rw} 

        Creates an SNMP community string.

         
        switch(config)# snmp-server community public ro 

        Configuring SNMP Notification Receivers

        You can configure Cisco Nexus 1000V to generate SNMP notifications to multiple host receivers.

        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 1000V 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 Cisco Nexus 1000V to authenticate and decrypt the inform s


        Before You Begin

        You must be in global configuration mode.

        Procedure
           Command or ActionPurpose
          Step 1switch(config)# snmp-server user name [auth {md5 | sha} passphrase [auto] [priv [aes-128] passphrase] [engineID id]

          Example:  

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

           
          switch(config)# snmp-server user NMS auth sha abcd1234 priv abcdefgh engineID 00:00:00:63:00:01:00:10:20:15:10:03

          Enabling SNMP Notifications

          You can enable or disable notifications. If you do not specify a notification name, Cisco Nexus 1000V enables all notifications.

          The following table lists the commands that enable the notifications for Cisco Nexus 1000V MIBs.


          Note


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


          MIB

          Related Commands

          All notifications

          snmp-server enable traps

          CISCO-AAA-SERVER-MIB

          snmp-server enable traps aaa

          ENITY-MIB

          snmp-server enable traps entity

          CISCO-ENTITY-FRU-CONTROL-MIB

          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

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

          Before You Begin

          You must be in global configuration mode to enable the specified notification

          Procedure
             Command or ActionPurpose
            Step 1switch(config)# snmp-server enable traps 

            Enables all SNMP notifications.

             
            Step 2switch(config)# snmp-server enable traps aaa [server-state-change] 

            Enables the AAA SNMP notifications.

             
            Step 3switch(config)# snmp-server enable traps entity [fru] 

            Enables the ENTITY-MIB SNMP notifications.

             
            Step 4switch(config)# snmp-server enable traps license 

            Enables the license SNMP notification.

             
            Step 5switch(config)# snmp-server enable traps link  

            Enables the link SNMP notifications.

             
            Step 6switch(config)# snmp-server enable traps port-security  

            Enables the port security SNMP notifications

             
            Step 7switch(config)# snmp-server enable traps snmp [authentication]  

            Enables the SNMP agent notifications.

             
            switch(config)# snmp-server enable traps 

            switch(config)# snmp-server enable traps aaa

            switch(config)# snmp-server enable traps entity

            switch(config)# snmp-server enable traps license

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

            switch(config)# snmp-server enable traps link 

            switch(config)# snmp-server enable traps snmp

            Disabling LinkUp/LinkDown 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).

            Before You Begin

            You must be in interface configuration mode to disable linkUp/linkDown notifications for the interface.

            Procedure
               Command or ActionPurpose
              Step 1switch(config-if)# no snmp trap link-status  

              Disables SNMP link-state traps for the interface. This command is enabled by default.

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

              Enabling a One-time Authentication for SNMP over TCP

              Before You Begin

              You must be in global configuration mode to enable one-time authentication for SNMP over TCP

              Procedure
                 Command or ActionPurpose
                Step 1switch(config)# snmp-server tcp-session [auth] 

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

                 
                switch(config)# snmp-server tcp-session

                Assigning the 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.

                Before You Begin

                Before beginning this procedure, you must be logged in to the CLI in EXEC mode.

                Procedure
                   Command or ActionPurpose
                  Step 1switch# configure terminal 

                  Enters global configuration mode.

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

                  Configures sysContact, which is the SNMP contact name.

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

                  Configures sysLocation, which is the SNMP location.

                   
                  Step 4switch(config)# show snmp  (Optional)

                  Displays information about one or more destination profiles.

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

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

                   
                  switch# configure terminal
                  Enter configuration commands, one per line.  End with CNTL/Z.
                  switch(config)# snmp contact Admin
                  switch(config)# snmp location Lab-7
                  switch(config)# show snmp
                  switch(config)# copy running-config startup-config

                  Configuring a Host Receiver for SNMPv3 Traps or Informs


                  Note


                  The SNMP manager must know the user credentials (authKey/PrivKey) based on the SNMP engine ID of the Cisco Nexus 1000V device to authenticate and decrypt the SNMPv3 messages


                  Before You Begin

                  You must be in global configuration mode.

                  Procedure
                     Command or ActionPurpose
                    Step 1switch(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.

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

                    Disabling SNMP

                    Before You Begin

                    You must be in global configuration mode to disable the SNMP protocol on a device.

                    Procedure
                       Command or ActionPurpose
                      Step 1 switch(config)# no snmp-server protocol enable 

                      Disables the SNMP protocol. This command is enabled by default.

                       
                      switch(config)# no snmp-server protocol enable

                      Modifying the AAA Synchronization Time

                      You can modify how long Cisco NX-OS holds the synchronized user configuration.

                      Before You Begin

                      You must be in global configuration mode.

                      Procedure
                         Command or ActionPurpose
                        Step 1 switch(config)# snmp-server aaa-user cache-timeout seconds 

                        Configures how long the AAA synchronized user configuration stays in the local cache. The range is from 1 to 86400 seconds. The default is 3600.

                         
                        switch(config)# snmp-server aaa-user cache-timeout 1200

                        Verifying the SNMP Configuration

                        Use one of the following commands to verify the configuration:

                        Command

                        Purpose

                        show running-config snmp [all]

                        Displays the SNMP running configuration.

                        show snmp

                        Displays the SNMP status.

                        show snmp community

                        Displays the SNMP community strings.

                        show snmp context

                        Displays the SNMP context mapping.

                        show snmp engineID

                        Displays the SNMP engineID.

                        show snmp group

                        Displays SNMP roles.

                        show snmp session

                        Displays SNMP sessions.

                        show snmp trap

                        Displays the SNMP notifications enabled or disabled.

                        show snmp user

                        Displays SNMPv3 users.

                        Configuration Example for SNMP

                        This example shows how to configure sending the Cisco linkUp/Down notifications to one notification host receiver using the Blue VRF and define two SNMP users, Admin and NMS

                        switch# configure terminal
                         switch(config)# snmp-server contact Admin@company.com 
                         switch(config)# snmp-server user Admin auth sha abcd1234 priv abcdefgh 
                         switch(config)# snmp-server user NMS auth sha abcd1234 priv abcdefgh engineID 00:00:00:63:00:01:00:22:32:15:10:03
                         switch(config)# snmp-server host 192.0.2.1 informs version 3 auth NMS
                         switch(config)# snmp-server host 192.0.2.1 use-vrf Blue
                         switch(config)# snmp-server enable traps link cisco

                        Related Documents for SNMP

                        MIBs

                        • CISCO-TC
                        • SNMPv2-MIB
                        • SNMP-COMMUNITY-MIB
                        • SNMP-FRAMEWORK-MIB
                        • SNMP-NOTIFICATION-MIB
                        • SNMP-TARGET-MIB
                        • ENTITY-MIB
                        • IF-MIB
                        • CISCO-ENTITY-EXT-MIB
                        • CISCO-ENTITY-FRU-CONTROL-MIB
                        • CISCO-FLASH-MIB
                        • CISCO-IMAGE-MIB
                        • CISCO-VIRTUAL-NIC-MIB
                        • CISCO-ENTITY-VENDORTYPE-OID-MIB
                        • NOTIFICATION-LOG-MIB
                        • IANA-ADDRESS-FAMILY-NUMBERS-MIB
                        • IANAifType-MIB
                        • IANAiprouteprotocol-MIB
                        • HCNUM-TC

                        To locate and download MIBs, go to the following URL:

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

                        • CISCO-VLAN-MEMBERSHIP-MIB
                        • CISCO-SYSTEM-MIB
                        • CISCO-SYSTEM-EXT-MIB
                        • CISCO-IMAGE-MIB
                        • CISCO-IMAGE-UPGRADE-MIB
                        • CISCO-BRIDGE-MIB
                        • CISCO-CONFIG-COPY-MIB
                        • CISCO-SYSLOG-EXT-MIB
                        • CISCO-PROCESS-MIB
                        • CISCO-AAA-SERVER-MIB
                        • CISCO-AAA-SERVER-EXT-MIB
                        • CISCO-COMMON-ROLES-MIB
                        • CISCO-COMMON-MGMT-MIB
                         

                        Feature History for SNMP

                        Feature Name

                        Releases

                        Feature Information

                        SNMP

                        4.0(4)SV1(1)

                        This feature was introduced.