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SNMP Configuration Guide, Cisco IOS XE Release 3E

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SNMPv3 Community MIB Support

SNMPv3 Community MIB Support

The SNMP Version 3 Community MIB Support feature provides support for the Simple Network Management Protocol Version 3 (SNMPv3) Community MIB (SNMP-COMMUNITY-MIB) module defined in RFC 2576, Coexistence between Version 1, Version 2, and Version 3 of the Internet-Standard Network Management Framework in Cisco IOS software. The SNMP Community MIB contains objects for mapping between the community strings and version-independent SNMP message parameters. This module discusses the requirements for interoperability between SNMP Version 1, SNMP Version 2c, and SNMP Version 3.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About SNMP Version 3

Security Features in SNMP Version 3

The security features provided in SNMPv3 are as follows:

  • Message integrity—Ensures that a packet has not been tampered with during transit.
  • Authentication—Determines that the message is from a valid source.
  • Encryption—Scrambles the content of a packet to prevent it from being learned by an unauthorized source.

SNMPv3 is a security model in which an authentication strategy is set up for a user and the group in which the user resides. 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 used when handling an SNMP packet.

The table below describes the combinations of SNMPv3 security models and levels.

Table 1 SNMP Version 3 Security Levels

Level

Authentication

Encryption

What Happens

noAuthNoPriv

Username

No

Uses a username match for authentication.

authNoPriv

Message Digest Algorithm 5 (MD5) or Secure Hash Algorithm (SHA)

No

Provides authentication based on the Hashed Message Authentication Code (HMAC)-MD5 or HMAC-SHA algorithms.

authPriv

MD5 or SHA

Data Encryption Standard (DES)

Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. In addition to authentication, provides DES 56-bit encryption based on the Cipher Block Chaining (CBC)-DES (DES-56) standard.

SNMPv3 supports RFCs 1901 to 1908, 2104, 2206, 2213, 2214, and 2271 to 2275. For more information about SNMPv3, see RFC 2570, Introduction to Version 3 of the Internet-standard Network Management Framework (this document is not a standard).

Cisco-Specific Error Messages for SNMP Version 3

Simple Network Management Protocol Version 3 (SNMPv3) provides different levels of security. If an authentication or an authorization request fails, a descriptive error message appears to indicate what went wrong. These error messages comply with RFC 3414, User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3).

You can use the snmp-server usm cisco command to disable the descriptive messages, thus preventing malicious users from misusing the information shown in the error messages. The table below describes the Cisco-specific error messages shown when the snmp-server usm cisco command is used, and the table compares these messages with the corresponding RFC 3414-compliant error messages.

Table 2 Cisco-Specific Error Messages for SNMPv3

Configured Security Level

Security Level of Incoming SNMP Message

RFC 3414-Compliant Error Indication

Cisco-Specific Error Messages

noAuthNoPriv

noAuthNoPriv

No error

No error

authNoPriv

unsupportedSecurityLevel

unknownUserName

authPriv

unsupportedSecurityLevel

unknownUserName

authNoPriv

noAuthNoPriv

AUTHORIZATION_ERROR

unknownUserName

authNoPriv with correct authentication password

No error

No error

authNoPriv with incorrect authentication password

wrongDigests

unknownUserName

authPriv

unsupportedSecurityLevel

unknownUserName

authPriv

noAuthNoPriv

AUTHORIZATION_ERROR

unknownUserName

authNoPriv with correct authentication password

AUTHORIZATION_ERROR

unknownUserName

authNoPriv with incorrect authentication password

AUTHORIZATION_ERROR

unknownUserName

authPriv with correct authentication password and correct privacy password

No error

No error

authPriv with correct authentication password and incorrect privacy password

No response

No response

authPriv with incorrect authentication password and correct privacy password

wrongDigests

unknownUserName

authPriv with incorrect authentication password and incorrect privacy password

wrongDigests

unknownUserName


Note


If an SNMP user belonging to an SNMP group is not configured with the password or if the group security level is not the same as the user security level, the error shown is “AUTHORIZATION_ERROR”. The Cisco-specific error message for this scenario is “unknownUserName”.


How to Configure SNMP Version 3

To configure the Simple Network Management Protocol Version 3 (SNMPv3) security mechanism and to use it to handle SNMP packets, you must configure SNMP groups and users with passwords.

Configuring the SNMP Server for SNMPv3

To configure a Simple Network Management Protocol Version 3 (SNMPv3) server user, specify an SNMP group or a table that maps SNMPv3 users to SNMP views. Then, specify the IP address or port number for the remote SNMP agent of the device where the user resides. Also, before you configure remote users for a particular agent, configure the SNMP engine ID by using the snmp-server engineID command for the remote agent. The SNMP engine ID of the remote agent is required to compute the authentication or privacy digests for the SNMP password. If the remote engine ID is not configured first, the configuration command will fail.

SNMP passwords are localized using the SNMP engine ID of the authoritative SNMP engine. For SNMP notifications such as inform requests, the authoritative SNMP agent is the remote agent. You must configure the SNMP engine ID of the remote agent in the SNMP database before you can send proxy requests or inform requests to it.


Note


An SNMPv3 user cannot be removed if the engine ID is changed after configuring the SNMP user. To remove the user, you must first reconfigure all the SNMP configurations.



Note


Default values do not exist for authentication or privacy algorithms when you configure the SNMP commands. Also, no default passwords exist. The minimum length for a password is one character, although we recommend that you use at least eight characters for security. If you forget a password, you cannot recover it and must reconfigure the user. You can specify either a plain text password or a localized Message Digest 5 (MD5) digest.


Perform this task to specify an SNMP server group name and to add a new user to an SNMP group.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    snmp-server group [group-name {v1 | v2c | v3 [auth | noauth | priv]}] [read read-view] [write write-view] [notify notify-view] [access access-list]

    4.    snmp-server engineID {local engine-id | remote ip-address [udp-port udp-port-number] [vrf vrf-name] engine-id-string}

    5.    snmp-server user user-name group-name [remote ip-address [udp-port port]] {v1 | v2c | v3 [encrypted] [auth {md5 | sha} auth-password]} [access access-list]

    6.    exit


DETAILED STEPS
      Command or Action Purpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.
     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 snmp-server group [group-name {v1 | v2c | v3 [auth | noauth | priv]}] [read read-view] [write write-view] [notify notify-view] [access access-list]


    Example:
    Device(config)# snmp-server group group1 v3 auth access lmnop
     

    Configures the SNMP server group to enable authentication for members of a specified named access list.

    • In this example, the SNMP server group group1 is configured to enable user authentication for members of the named access list lmnop.
     
    Step 4 snmp-server engineID {local engine-id | remote ip-address [udp-port udp-port-number] [vrf vrf-name] engine-id-string}


    Example:
    Device(config)# snmp-server engineID remote 172.16.15.4 udp-port 120 1a2833c0129a
     

    Configures the SNMP engine ID.

    • In this example, the SNMP engine ID is configured for a remote user.
     
    Step 5 snmp-server user user-name group-name [remote ip-address [udp-port port]] {v1 | v2c | v3 [encrypted] [auth {md5 | sha} auth-password]} [access access-list]


    Example:
    Device(config)# snmp-server user user1 group1 v3 auth md5 password123 
     

    Adds a new user to an SNMPv3 group and configures a plain text password for the user.

    Note   

    For the auth-password argument, the minimum length is one character; the recommended length is at least eight characters, and the password should include both letters and numbers.

    Note   

    If you have the localized MD5 or Secure Hash Algorithm (SHA) digest, you can specify the digest instead of the plain text password. The digest should be formatted as aa:bb:cc:dd, where aa, bb, cc, and dd are hexadecimal values. Also, the digest should be exactly 16 octets in length.

     
    Step 6 exit


    Example:
    Device(config)# exit
     

    Exits global configuration mode.

     

    Verifying SNMP Version 3

    Perform this task to verify the Simple Network Management Protocol Version 3 (SNMPv3) configuration. The show commands can be entered in any order.

    SUMMARY STEPS

      1.    enable

      2.    show snmp group

      3.    show snmp user [username]

      4.    show snmp engineID


    DETAILED STEPS
        Command or Action Purpose
      Step 1 enable


      Example:
      Device> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.
       
      Step 2 show snmp group


      Example:
      Device# show snmp group
      
      groupname: V1                               security model:v1 
      readview : v1default                        writeview: <no writeview specified> 
      notifyview: <no notifyview specified>       
      row status: active
      groupname: ILMI                             security model:v1 
      readview : *ilmi                            writeview: *ilmi                    
      notifyview: <no notifyview specified>       
      row status: active
      groupname: ILMI                             security model:v2c 
      readview : *ilmi                            writeview: *ilmi                    
      notifyview: <no notifyview specified>       
      row status: active
      groupname: group1                           security model:v1 
      readview : v1default                        writeview: <no writeview specified> 
      notifyview: <no notifyview specified>       
      row status: active
       

      Displays information about each SNMP group in the network.

      Displays information about each SNMP group in the network.

       
      Step 3 show snmp user [username]


      Example:
      Device# show snmp user user1
      
      User name: user1
      Engine ID: 00000009020000000C025808
      storage-type: nonvolatile active access-list: 10
      Rowstatus: active
      Authentication Protocol: MD5
      Privacy protocol: DES
      Group name: group1
       

      Displays information about configured characteristics of an SNMP user.

       
      Step 4 show snmp engineID


      Example:
      Device# show snmp engineID
      
      Local SNMP engineID: 1A2836C0129A
      Remote Engine ID        IP-addr    Port
      1A2833C0129A            remote     10.2.28.1 120
       

      Displays information about the SNMP engine ID that is configured for an SNMP user.

       

      Configuration Examples for SNMP Version 3

      Example: Configuring SNMP Version 3

      The following example shows how to enable Simple Network Management Protocol Version 3 (SNMPv3). The configuration permits any SNMP manager to access all objects with read-only permissions using the community string named “public”. This configuration does not cause the device to send traps.

      Device(config)# snmp-server community public

      The following example shows how to configure a remote user to receive traps at the “noAuthNoPriv” security level when the SNMPv3 security model is enabled:

      Device(config)# snmp-server group group1 v3 noauth
      Device(config)# snmp-server user remoteuser1 group1 remote 10.12.8.4
      Device(config)# snmp-server host 10.12.8.4 informs version 3 noauth remoteuser config

      The following example shows how to configure a remote user to receive traps at the “authNoPriv” security level when the SNMPv3 security model is enabled:

      Device(config)# snmp-server group group2 v3 auth
      Device(config)# snmp-server user AuthUser group2 remote 10.12.8.4 v3 auth md5 password1

      The following example shows how to configure a remote user to receive traps at the “priv” security level when the SNMPv3 security model is enabled:

      Device(config)# snmp-server group group3 v3 priv
      Device(config)# snmp-server user PrivateUser group3 remote 10.12.8.4 v3 auth md5 password1 priv access des56

      Additional References for SNMP Version 3

      Related Documents

      Related Topic

      Document Title

      Cisco IOS commands

      Cisco IOS Master Command List, All Releases

      SNMP commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples

      Cisco IOS SNMP Support Command Reference

      Standards and RFCs

      Standard/RFC

      Title

      RFC 2104

      HMAC: Keyed-Hashing for Message Authentication

      RFC 2570

      Introduction to Version 3 of the Internet-standard Network Management Framework

      RFC 2576

      Coexistence between Version 1, Version 2, and Version 3 of the Internet-standard Network Management Framework

      RFC 3413

      SNMPv3 Applications

      RFC 3414

      User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)

      RFC 3415

      View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)

      MIBs

      MIB

      MIBs Link

      SNMP-COMMUNITY-MIB

      To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

      http:/​/​www.cisco.com/​go/​mibs

      Technical Assistance

      Description

      Link

      The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

      http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

      Feature Information for SNMP Version 3

      The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

      Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

      Table 3 Feature Information for SNMP Version 3

      Feature Name

      Releases

      Feature Information

      SNMP Version 3

      12.0(3)T

      12.0(6)S

      12.1(3)T

      12.1(14)

      12.2(13)T

      15.0(1)S

      The SNMP Version 3 feature is used to provide secure access to devices by authenticating and encrypting data packets over the network.

      SNMP Version 3 Community MIB Support

      12.0(22)S

      12.2(4)T

      12.2(11)T

      12.2(18)S

      15.0(1)S

      Cisco IOS XE Release 3.1.0SG

      15.2(1)E

      Cisco IOS XE Release 3E

      The SNMP Version 3 Community MIB Support feature implements support for the SNMP Community MIB module (SNMPCOMMUNITY-MIB), defined in RFC 2576, in Cisco IOS software.

      s