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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.
This section includes the following topics:
The SNMP framework consists of three parts:
SNMP is defined in RFCs 3411 to 3418.
Cisco CG-OS supports SNMPv2c, and SNMPv3. SNMPv2c uses a community-based form of security.
Cisco CG-OS supports SNMP over IPv4 and IPv6.
Note CG-OS does not support multiple VDCs. It always uses the default VDC (VDC 1).
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.
Cisco CG-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. Cisco CG-OS 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 Cisco CG-OS never receives a response, it can send the inform request again.
You can configure Cisco CG-OS to send notifications to multiple host receivers. See the “Configuring SNMP Notification Receivers” section for more information about host receivers.
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:
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.
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:
Three security models are available: SNMPv2c, and SNMPv3. The security model combined with the security level determine the security mechanism applied when the SNMP message is processed.
Table 3-1 identifies what the combinations of security models and levels mean.
The SNMPv3 User-Based Security Model (USM) refers to SNMP message-level security and offers the following services:
SNMPv3 authorizes management operations only by configured users and encrypts SNMP messages.
Cisco CG-OS uses two authentication protocols for SNMPv3:
Cisco CG-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 and the aes-128 token indicate 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.
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 CG-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 router.
Any configuration changes made to the user group, role, or password results in database synchronization for both SNMP and AAA.
Cisco CG-OS synchronizes user configuration in the following ways:
Note When you configure a passphrase/password in localized key/encrypted format, Cisco CG-OS does not synchronize the user information (password, roles, and so on).
Cisco CG-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.
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.
To locate and download the MIBs supported by Cisco CG-OS, visit the Cisco MIB Locator page:
http://tools.cisco.com/ITDIT/MIBS/servlet/index
For a list of supported MIBs and MIB notifications, see Table 3-3 .
Table 3-2 lists the default settings for SNMP parameters.
This section includes the following topics:
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 CG-OS responds with an authorizationError for any SNMPv3 PDU request using securityLevel parameter of either noAuthNoPriv or authNoPriv.
Use the following command in global configuration mode to enforce SNMP message encryption for a user:
Use the following command in global configuration mode to enforce SNMP message encryption for all users:
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.
Use the following command in global configuration mode to assign a role to an SNMP user:
You can create SNMP communities for SNMPv2c.
Use the following command in global configuration mode to create an SNMP community string:
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:
See the Cisco 1000 Series Connected Grid Routers Security Software Configuration Guide for more information on creating ACLs. The ACL applies to IPv4 over UDP and TCP.
Use the following command in global configuration mode to assign an ACL to a community to filter SNMP requests:
You can configure Cisco CG-OS to generate SNMP notifications to multiple SNMPv2c and SNMPv3 host receivers.
Use the following command in global configuration mode to configure a host receiver for SNMPv2c traps or informs:
Use the following command in global configuration mode to configure 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 CG-OS device to authenticate and decrypt the SNMPv3 messages.
You can configure SNMP to use the IP address of an interface as the source IP address for notifications. When a notification is generated, its source IP address is based on the IP address of this configured interface. You can configure this as follows:
Note Configuring the source interface IP address for outgoing trap packets does not guarantee that the device will use the same interface to send the trap. The source interface IP address defines the source address inside of the SNMP trap, and the connection is opened with the address of the egress interface as source.
Use the following command in global configuration mode to configure a host receiver on a source interface:
Use the following command in global configuration mode to configure a source interface for sending out all SNMP notifications:
Use the show snmp source-interface command to display information about configured source interfaces.
You must configure a notification target user on the device to send SNMPv3 inform notifications to a notification host receiver.
Cisco CG-OS 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 CG-OS to authenticate and decrypt the informs.
Use the following command in global configuration mode to configure the notification target user:
You can configure SNMP to send traps using an inband port. To do so, you must configure the source interface (at the global or host level) to send the traps.
This example shows how to configure SNMP to send traps using a globally configured inband port:
You can enable or disable notifications. If you do not specify a notification name, Cisco CG-OS enables all notifications.
Table 3-3 lists the commands that enable the notifications for Cisco CG-OS MIBs.
Note The snmp-server enable traps command enables both traps and informs, depending on the configured notification host receivers.
Use the following commands in global configuration mode to enable the specified notification.
You can disable linkUp and linkDown notifications on an individual interface. You can use these limit notifications on a flapping interface (an interface that transitions between up and down repeatedly).
Use the following command in interface configuration mode to disable linkUp/linkDown notifications for the interface:
The SNMP ifIndex is used across multiple SNMP MIBs to link related interface information. The ifIndex is also used by NetFlow to collect information on an interface.
Use the following command in any mode to display the SNMP ifIndex values for interfaces:
You can enable a one-time authentication for SNMP over a TCP session.
Use the following command in global configuration mode to enable a one-time authentication for SNMP over TCP:
You can assign the device contact information, which is limited to 32 characters (without spaces) and the device location.
You can configure an SNMP context to map to a logical network entity, such as a protocol instance.
This example shows how to map OSPF instance Enterprise to the same SNMPv2c public community string.
router(config)# copy running-config startup-config
This example shows how to delete the mapping between an SNMP context and a logical network entity when operating in the global configuration mode.
router(config)# no snmp-server context public1
Note When deleting a context mapping (see example above), you only enter the context name in the no snmp-server context context-name command. You do not enter the instance or topology keywords and variable names as you did when configuring the item (see Step 2. If you use the instance or topology keywords when deleting the context mapping, then you configure a mapping between the context and a zero-length string
You can disable SNMP on a device.
Use the following command in global configuration mode to disable SNMP:
To display the SNMP configuration information, perform one of the following tasks.
This example shows how to configure Cisco CG-OS to send the Cisco linkUp or Down notifications to one notification host receiver and defines two SNMP users, Admin and NMS.
This example shows how to configure SNMP to send traps using an inband port configured at the host level.
Source interface: Ethernet 1/2
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To locate and download these MIBs, go to the following URL: http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml |