Cisco ASR 9000 Series Aggregation Services Router System Management Configuration Guide, Release 5.3.x

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Book Title

Cisco ASR 9000 Series Aggregation Services Router System Management Configuration Guide, Release 5.3.x

Chapter Title

Configuring Simple Network Management Protocol

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Updated:
January 6, 2015

Chapter: Configuring Simple Network Management Protocol

Configuring Simple Network Management Protocol

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 module describes the new and revised tasks you need to implement SNMP on your Cisco IOS XR network.

For detailed conceptual information about SNMP on the Cisco IOS XR software and complete descriptions of the SNMP commands listed in this module, see Related Documents. For information on specific MIBs, refer to Cisco ASR 9000 Series Aggregation Services Routers MIB Specifications Guide. To locate documentation for other commands that might appear in the course of performing a configuration task, search online in Cisco ASR 9000 Series Aggregation Services Router Commands Master List.

Table 1. Feature History for Implementing SNMP on Cisco IOS XR Software

Release

Modification

Release 3.7.2

This feature was introduced.

Release 3.9.0

Support was added for 3DES and AES encryption.

The ability to preserve ENTITY-MIB and CISCO-CLASS-BASED-QOS-MIB data was added.

Release 4.2.0

Support was added for SNMP over IPv6.

This module contains the following topics:

Prerequisites for Implementing SNMP

You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.

Restrictions for SNMP Use on Cisco IOS XR Software

SNMP outputs are only 32-bits wide and therefore cannot display any information greater than 232. 232 is equal to 4.29 Gigabits. Note that a 10 Gigabit interface is greater than this and so if you are trying to display speed information regarding the interface, you might see concatenated results.

Information About Implementing SNMP

To implement SNMP, you need to understand the concepts described in this section.

SNMP Functional Overview

The SNMP framework consists of three parts:

  • SNMP manager
  • SNMP agent
  • Management Information Base (MIB)

SNMP Manager

The SNMP manager is the system used to control and monitor the activities of network hosts using SNMP. The most common managing system is called a network management system (NMS). The term NMS can be applied to either a dedicated device used for network management, or the applications used on such a device. A variety of network management applications are available for use with SNMP. These features range from simple command-line applications to feature-rich graphical user interfaces (such as the CiscoWorks 2000 line of products).

SNMP Agent

The SNMP agent is the software component within the managed device that maintains the data for the device and reports these data, as needed, to managing systems. The agent and MIB reside on the router. To enable the SNMP agent, you must define the relationship between the manager and the agent.

MIB

The Management Information Base (MIB) is a virtual information storage area for network management information, which consists of collections of managed objects. Within the MIB there are collections of related objects, defined in MIB modules. MIB modules are written in the SNMP MIB module language, as defined in STD 58, RFC 2578, RFC 2579, and RFC 2580. Note that individual MIB modules are also referred to as MIBs; for example, the Interfaces Group MIB (IF-MIB) is a MIB module within the MIB on your system.

The SNMP agent contains MIB variables whose values the SNMP manager can request or change through Get or Set operations. A manager can get a value from an agent or store a value into that agent. The agent gathers data from the MIB, the repository for information about device parameters and network data. The agent can also respond to manager requests to get or set data.

This figure illustrates the communications relationship between the SNMP manager and agent. A manager can send the agent requests to get and set MIB values. The agent can respond to these requests. Independent of this interaction, the agent can send unsolicited notifications (traps) to the manager to notify the manager of network conditions.

Figure 1. Communication Between an SNMP Agent and Manager

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. On Cisco IOS XR software, unsolicited (asynchronous) notifications can be generated only as traps. Traps are messages alerting the SNMP manager to a condition on the network. Notifications can indicate improper user authentication, restarts, the closing of a connection, loss of connection to a neighbor router, or other significant events.


Note

Inform requests (inform operations) are supported in Cisco IOS XR software from release 4.1 onwards. For more information see, #http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r5-3/sysman/command/reference/b-sysman-cr53xasr/b-sysman-cr53xasr_chapter_010010.html#wp2863682680

Traps are less reliable than informs because the receiver does not send any acknowledgment when it receives a trap. The sender 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 manager does not receive an inform request, it does not send a response. If the sender never receives a response, the inform request can be sent again. Thus, informs are more likely to reach their intended destination.

However, traps are often preferred because informs consume more resources in the router and in the network. Unlike a trap, which is discarded as soon as it is sent, an inform request must be held in memory until a response is received or the request times out. Also, traps are sent only once, and an inform may be retried several times. The retries increase traffic and contribute to a higher overhead on the network. Thus, traps and inform requests provide a trade-off between reliability and resources.

Figure 2. Trap Received by the SNMP Manager. In this illustration, the agent router sends a trap to the SNMP manager. Although the manager receives the trap, it does not send any acknowledgment to the agent. The agent has no way of knowing that the trap reached its destination.


Figure 3. Trap Not Received by the SNMP Manager. In this illustration, the agent sends a trap to the manager, but the trap does not reach the manager. Because the agent has no way of knowing that the trap did not reach its destination, the trap is not sent again. The manager never receives the trap.


SNMP Versions

Cisco IOS XR software supports the following versions of SNMP:

  • Simple Network Management Protocol Version 1 (SNMPv1)
  • Simple Network Management Protocol Version 2c (SNMPv2c)
  • Simple Network Management Protocol Version 3 (SNMPv3)

Both SNMPv1 and SNMPv2c use a community-based form of security. The community of managers able to access the agent MIB is defined by an IP address access control list and password.

SNMPv2c support includes a bulk retrieval mechanism and more detailed error message reporting to management stations. The bulk retrieval mechanism supports the retrieval of tables and large quantities of information, minimizing the number of round-trips required. The SNMPv2c improved error handling support includes expanded error codes that distinguish different kinds of error conditions; these conditions are reported through a single error code in SNMPv1. Error return codes now report the error type. Three kinds of exceptions are also reported: no such object exceptions, no such instance exceptions, and end of MIB view exceptions.

SNMPv3 is a security model. A security model is an authentication strategy that is set up for a user and the group 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 will determine which security mechanism is employed when an SNMP packet is handled. See Table 1 for a list of security levels available in SNMPv3. The SNMPv3 feature supports RFCs 3411 to 3418.

You must configure the SNMP agent to use the version of SNMP supported by the management station. An agent can communicate with multiple managers; for this reason, you can configure the Cisco IOS-XR software to support communications with one management station using the SNMPv1 protocol, one using the SNMPv2c protocol, and another using SMNPv3.

Comparison of SNMPv1, v2c, and v3

SNMP v1, v2c, and v3 all support the following operations:

  • get-request—Retrieves a value from a specific variable.

  • get-next-request—Retrieves the value following the named variable; this operation is often used to retrieve variables from within a table. With this operation, an SNMP manager does not need to know the exact variable name. The SNMP manager searches sequentially to find the needed variable from within the MIB.

  • get-response—Operation that replies to a get-request, get-next-request, and set-request sent by an NMS.

  • set-request—Operation that stores a value in a specific variable.

  • trap—Unsolicited message sent by an SNMP agent to an SNMP manager when some event has occurred.

The below table identifies other key SNMP features supported by the SNMP v1, v2c, and v3.

Table 2. SNMPv1, v2c, and v3 Feature Support

Feature

SNMP v1

SNMP v2c

SNMP v3

Get-Bulk Operation

No

Yes

Yes

Inform Operation

No

Yes (No on the Cisco IOS XR software)

Yes (No on the Cisco IOS XR software)

64 Bit Counter

No

Yes

Yes

Textual Conventions

No

Yes

Yes

Authentication

No

No

Yes

Privacy (Encryption)

No

No

Yes

Authorization and Access Controls (Views)

No

No

Yes

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

Table 3. 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 HMAC1-MD52 algorithm or the HMAC-SHA3.

v3

authPriv

HMAC-MD5 or HMAC-SHA

DES

Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Provides DES4 56-bit encryption in addition to authentication based on the CBC5 DES (DES-56) standard.

v3

authPriv

HMAC-MD5 or HMAC-SHA

3DES

Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Provides 168-bit 3DES6 level of encryption.

v3

authPriv

HMAC-MD5 or HMAC-SHA

AES

Provides authentication based on the HMAC-MD5 or HMAC-SHA algorithms. Provides 128-bit AES7 level of encryption.

1 Hash-Based Message Authentication Code
2 Message Digest 5
3 Secure Hash Algorithm
4 Data Encryption Standard
5 Cipher Block Chaining
6 Triple Data Encryption Standard
7 Advanced Encryption Standard

Use of 3DES and AES encryption standards requires that the security package (k9sec) be installed. For information on installing software packages, see Upgrading and Managing Cisco IOS XR Software.

SNMPv3 Benefits

SNMPv3 provides secure access to devices by providing authentication, encryption and access control. These added security benefits secure SNMP against the following security threats:

  • Masquerade—The threat that an SNMP user may assume the identity of another SNMP user to perform management operations for which that SNMP user does not have authorization.
  • Message stream modification—The threat that messages may be maliciously reordered, delayed, or replayed (to an extent that is greater than can occur through the natural operation of a subnetwork service) to cause SNMP to perform unauthorized management operations.
  • Disclosure—The threat that exchanges between SNMP engines could be eavesdropped. Protecting against this threat may be required as a matter of local policy.

In addition, SNMPv3 provides access control over protocol operations on SNMP managed objects.

SNMPv3 Costs

SNMPv3 authentication and encryption contribute to a slight increase in the response time when SNMP operations on MIB objects are performed. This cost is far outweighed by the security advantages provided by SNMPv3.

This table shows the order of response time (from least to greatest) for the various security model and security level combinations.

Table 4. Order of Response Times from Least to Greatest

Security Model

Security Level

SNMPv2c

noAuthNoPriv

SNMPv3

noAuthNoPriv

SNMPv3

authNoPriv

SNMPv3

authPriv

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.

USM uses two authentication protocols:

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

USM uses Cipher Block Chaining (CBC)-DES (DES-56) as the privacy protocol for message encryption.

View-Based Access Control Model

The View-Based Access Control Model (VACM) enables SNMP users to control access to SNMP managed objects by supplying read, write, or notify access to SNMP objects. It prevents access to objects restricted by views. These access policies can be set when user groups are configured with the snmp-server group command.

MIB Views

For security reasons, it is often valuable to be able to restrict the access rights of some groups to only a subset of the management information within the management domain. To provide this capability, access to a management object is controlled through MIB views, which contain the set of managed object types (and, optionally, the specific instances of object types) that can be viewed.

Access Policy

Access policy determines the access rights of a group. The three types of access rights are as follows:

  • read-view access—The set of object instances authorized for the group when objects are read.
  • write-view access—The set of object instances authorized for the group when objects are written.
  • notify-view access—The set of object instances authorized for the group when objects are sent in a notification.

IP Precedence and DSCP Support for SNMP

SNMP IP Precedence and differentiated services code point (DSCP) support delivers QoS specifically for SNMP traffic. You can change the priority setting so that SNMP traffic generated in a router is assigned a specific QoS class. The IP Precedence or IP DSCP code point value is used to determine how packets are handled in weighted random early detection (WRED).

After the IP Precedence or DSCP is set for the SNMP traffic generated in a router, different QoS classes cannot be assigned to different types of SNMP traffic in that router.

The IP Precedence value is the first three bits in the type of service (ToS) byte of an IP header. The IP DSCP code point value is the first six bits of the differentiate services (DiffServ Field) byte. You can configure up to eight different IP Precedence markings or 64 different IP DSCP markings.

Session MIB support on subscriber sessions

SNMP monitoring requires information about subscribers of all types. The CISCO-SUBSCRIBER-SESSION-MIB is defined to model per-subscriber data as well as aggregate subscriber (PPPoE) data. It is required to support notifications (traps) for aggregate session counts crossing configured thresholds. Generic MIB Data Collector Manager (DCM) support for CISCO-SUBSCRIBER-SESSION-MIB, helps faster data collection and also better handling of parallel data.

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. On Cisco IOS XR software, unsolicited (asynchronous) notifications can be generated only as traps. Traps are messages alerting the SNMP manager to a condition on the network. Notifications can indicate improper user authentication, restarts, the closing of a connection, loss of connection to a neighbor router, or other significant events.


Note

Inform requests (inform operations) are supported in Cisco IOS XR software from release 4.1 onwards. For more information see, #http://www.cisco.com/c/en/us/td/docs/routers/asr9000/software/asr9k_r5-3/sysman/command/reference/b-sysman-cr53xasr/b-sysman-cr53xasr_chapter_010010.html#wp2863682680

Traps are less reliable than informs because the receiver does not send any acknowledgment when it receives a trap. The sender 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 manager does not receive an inform request, it does not send a response. If the sender never receives a response, the inform request can be sent again. Thus, informs are more likely to reach their intended destination.

However, traps are often preferred because informs consume more resources in the router and in the network. Unlike a trap, which is discarded as soon as it is sent, an inform request must be held in memory until a response is received or the request times out. Also, traps are sent only once, and an inform may be retried several times. The retries increase traffic and contribute to a higher overhead on the network. Thus, traps and inform requests provide a trade-off between reliability and resources.

Figure 4. Trap Received by the SNMP Manager. In this illustration, the agent router sends a trap to the SNMP manager. Although the manager receives the trap, it does not send any acknowledgment to the agent. The agent has no way of knowing that the trap reached its destination.


Figure 5. Trap Not Received by the SNMP Manager. In this illustration, the agent sends a trap to the manager, but the trap does not reach the manager. Because the agent has no way of knowing that the trap did not reach its destination, the trap is not sent again. The manager never receives the trap.


Session Types

The supported session types are:

  • PPPoE

  • IP SUB PKT

  • IP SUB DHCP

How to Implement SNMP on Cisco IOS XR Software

This section describes how to implement SNMP.

The snmp-server commands enable SNMP on Management Ethernet interfaces by default. For information on how to enable SNMP server support on other inband interfaces, see the Implementing Management Plane Protection on Cisco IOS XR Software module in System Security Configuration Guide for Cisco ASR 9000 Series Routers.

Configuring SNMPv3

This task explains how to configure SNMPv3 for network management and monitoring.


Note

No specific command enables SNMPv3; the first snmp-server global configuration command (config), that you issue enables SNMPv3. Therefore, the sequence in which you issue the snmp-server commands for this task does not matter.

SUMMARY STEPS

  1. configure
  2. snmp-server view view-name oid-tree {included | excluded }
  3. snmp-server group name {v1 | v2c | v3 {auth | noauth | priv }} [read view] [write  view] [notify view] [access-list-name]
  4. snmp-server user username groupname {v1  | v2c  | v3  [auth  {md5 | sha } {clear | encrypted } auth-password [priv des56 {clear | encrypted } priv-password]]} [access-list-name]
  5. commit

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

snmp-server view view-name oid-tree {included | excluded }

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server view 
view_name 1.3.6.1.2.1.1.5 included

Creates or modifies a view record.

Step 3

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

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server group 
group_name v3 noauth read view_name1 write view_name2

Configures a new SNMP group or a table that maps SNMP users to SNMP views.

Step 4

snmp-server user username groupname {v1  | v2c  | v3  [auth  {md5 | sha } {clear | encrypted } auth-password [priv des56 {clear | encrypted } priv-password]]} [access-list-name]

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server user 
noauthuser group_name v3

Configures a new user to an SNMP group.

Note 

Only one remote host can be assigned to the same username for SNMP version 3. If you configure the same username with different remote hosts, only the last username and remote host combination will be accepted and will be seen in the show running configuration. In the case of multiple SNMP managers, multiple unique usernames are required.

Step 5

commit

Configuring SNMP Trap Notifications

This task explains how to configure the router to send SNMP trap notifications.


Note

You can omit 3 if you have already completed the steps documented under the Configuring SNMPv3 task.

SUMMARY STEPS

  1. configure
  2. snmp-server group name {v1 | v2c | v3 {auth | noauth | priv }} [read view] [write  view] [notify view] [access-list-name]
  3. snmp-server user username groupname {v1  | v2c  | v3  [auth  {md5 | sha } {clear | encrypted } auth-password [priv des56 {clear | encrypted } priv-password]]} [access-list-name]
  4. snmp-server host address [traps ] [version {1 | 2c | 3 [auth | noauth | priv ]}] community-string [udp-port port] [notification-type]
  5. snmp-server traps [notification-type]
  6. commit
  7. (Optional) show snmp host

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

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

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server group 
group_name v3 noauth read view_name1 write view_name2

Configures a new SNMP group or a table that maps SNMP users to SNMP views.

Step 3

snmp-server user username groupname {v1  | v2c  | v3  [auth  {md5 | sha } {clear | encrypted } auth-password [priv des56 {clear | encrypted } priv-password]]} [access-list-name]

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server user 
noauthuser group_name v3

Configures a new user to an SNMP group.

Note 

Only one remote host can be assigned to the same username for SNMP version 3. If you configure the same username with different remote hosts, only the last username and remote host combination will be accepted and will be seen in the show running configuration. In the case of multiple SNMP managers, multiple unique usernames are required.

Step 4

snmp-server host address [traps ] [version {1 | 2c | 3 [auth | noauth | priv ]}] community-string [udp-port port] [notification-type]

Example:

RP/0/RP0/CPU0:router(config)# snmp-server host 12.26.25.61 traps version 3 
noauth userV3noauth

Specifies SNMP trap notifications, the version of SNMP to use, the security level of the notifications, and the recipient (host) of the notifications.

Step 5

snmp-server traps [notification-type]

Example:

RP/0/RP0/CPU0:router(config)# snmp-server traps bgp

Enables the sending of trap notifications and specifies the type of trap notifications to be sent.

  • If a trap is not specified with the notification-type argument, all supported trap notifications are enabled on the router. To display which trap notifications are available on your router, enter the snmp-server traps ? command.
Step 6

commit

Step 7

(Optional) show snmp host

Example:


RP/0/RSP0/CPU0:router# show snmp host
 (Optional)

Displays information about the configured SNMP notification recipient (host), port number, and security model.

Setting the Contact, Location, and Serial Number of the SNMP Agent

This task explains how to set the system contact string, system location string, and system serial number of the SNMP agent.


Note

The sequence in which you issue the snmp-server commands for this task does not matter.

SUMMARY STEPS

  1. configure
  2. (Optional) snmp-server contact system-contact-string
  3. (Optional) snmp-server location system-location
  4. (Optional) snmp-server chassis-id serial-number
  5. commit

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

(Optional) snmp-server contact system-contact-string

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server contact 
Dial System Operator at beeper # 27345
 (Optional)

Sets the system contact string.

Step 3

(Optional) snmp-server location system-location

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server location 
Building 3/Room 214
(Optional)

Sets the system location string.
Step 4

(Optional) snmp-server chassis-id serial-number

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server chassis-id 1234456
 (Optional)

Sets the system serial number.
Step 5

commit

Defining the Maximum SNMP Agent Packet Size

This task shows how to configure the largest SNMP packet size permitted when the SNMP server is receiving a request or generating a reply.


Note

The sequence in which you issue the snmp-server commands for this task does not matter.

SUMMARY STEPS

  1. configure
  2. (Optional) snmp-server packetsize byte-count
  3. commit

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

(Optional) snmp-server packetsize byte-count

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server packetsize 1024
 (Optional)

Sets the maximum packet size.
Step 3

commit

Changing Notification Operation Values

After SNMP notifications have been enabled, you can specify a value other than the default for the source interface, message queue length, or retransmission interval.

This task explains how to specify a source interface for trap notifications, the message queue length for each host, and the retransmission interval.


Note

The sequence in which you issue the snmp-server commands for this task does not matter.

SUMMARY STEPS

  1. configure
  2. (Optional) snmp-server trap-source type interface-path-id
  3. (Optional) snmp-server queue-length length
  4. (Optional) snmp-server trap-timeout seconds
  5. commit

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

(Optional) snmp-server trap-source type interface-path-id

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server trap-source POS 0/0/1/0
 (Optional)

Specifies a source interface for trap notifications.

Step 3

(Optional) snmp-server queue-length length

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server queue-length 20
 (Optional)

Establishes the message queue length for each notification.

Step 4

(Optional) snmp-server trap-timeout seconds

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server trap-timeout 20
 (Optional)

Defines how often to resend notifications on the retransmission queue.

Step 5

commit

Setting IP Precedence and DSCP Values

This task describes how to configure IP Precedence or IP DSCP for SNMP traffic.

Before you begin

SNMP must be configured.

SUMMARY STEPS

  1. configure
  2. Use one of the following commands:
    • snmp-server ipv4 precedence value
    • snmp-server ipv4 dscp value
  3. commit

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

Use one of the following commands:

  • snmp-server ipv4 precedence value
  • snmp-server ipv4 dscp value

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server dscp 24

Configures an IP precedence or IP DSCP value for SNMP traffic.

Step 3

commit

Configuring MIB Data to be Persistent

Many SNMP MIB definitions define arbitrary 32-bit indices for their object tables. MIB implementations often do a mapping from the MIB indices to some internal data structure that is keyed by some other set of data. In these MIB tables the data contained in the table are often other identifiers of the element being modelled. For example, in the ENTITY-MIB, entries in the entPhysicalTable are indexed by the 31-bit value, entPhysicalIndex, but the entities could also be identified by the entPhysicalName or a combination of the other objects in the table.

Because of the size of some MIB tables, significant processing is required to discover all the mappings from the 32-bit MIB indices to the other data which the network management station identifies the entry. For this reason, it may be necessary for some MIB indices to be persistent across process restarts, switchovers, or device reloads. The ENTITY-MIB entPhysicalTable and CISCO-CLASS-BASED-QOS-MIB are two such MIBs that often require index values to be persistent.

Also, because of query response times and CPU utilization during CISCO-CLASS-BASED-QOS-MIB statistics queries, it is desirable to cache service policy statistics.

SUMMARY STEPS

  1. (Optional) snmp-server entityindex persist
  2. (Optional) snmp-server mibs cbqosmib persist
  3. (Optional) snmp-server cbqosmib cache refresh time time
  4. (Optional) snmp-server cbqosmib cache service-policy count count
  5. snmp-server ifindex persist

DETAILED STEPS

  Command or Action Purpose
Step 1

(Optional) snmp-server entityindex persist

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server entityindex persist
(Optional)

Enables the persistent storage of ENTITY-MIB data.
Step 2

(Optional) snmp-server mibs cbqosmib persist

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server mibs cbqosmib persist
(Optional)

Enables persistent storage of the CISCO-CLASS-BASED-QOS-MIB data.
Step 3

(Optional) snmp-server cbqosmib cache refresh time time

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server mibs cbqosmib cache 
refresh time 45
(Optional)

Enables QoS MIB caching with a specified cache refresh time.
Step 4

(Optional) snmp-server cbqosmib cache service-policy count count

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server mibs cbqosmib cache 
service-policy count 50
(Optional)

Enables QoS MIB caching with a limited number of service policies to cache.
Step 5

snmp-server ifindex persist

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server ifindex persist

Enables ifIndex persistence globally on all Simple Network Management Protocol (SNMP) interfaces.

Configuring LinkUp and LinkDown Traps for a Subset of Interfaces

By specifying a regular expression to represent the interfaces for which you are interested in setting traps, you can enable or disable linkUp and linkDown traps for a large number of interfaces simultaneously.

Before you begin

SNMP must be configured.

SUMMARY STEPS

  1. configure
  2. snmp-server interface subset subset-number regular-expression expression
  3. notification linkupdown disable
  4. commit
  5. (Optional) show snmp interface notification subset subset-number
  6. (Optional) show snmp interface notification regular-expression expression
  7. (Optional) show snmp interface notification type interface-path-id

DETAILED STEPS

  Command or Action Purpose
Step 1

configure

Step 2

snmp-server interface subset subset-number regular-expression expression

Example:


RP/0/RSP0/CPU0:router(config)# snmp-server interface subset 10 
    regular-expression "^Gig[a-zA-Z]+[0-9/]+\."
RP/0/RSP0/CPU0:router(config-snmp-if-subset)#

Enters snmp-server interface mode for the interfaces identified by the regular expression.

The subset-number argument identifies the set of interfaces, and also assigns a priority to the subset in the event that an interface is included in more than one subset. Lower numbers have higher priority and their configuration takes precedent over interface subsets with higher numbers.

The expression argument must be entered surrounded by double quotes.

Refer to the Understanding Regular Expressions, Special Characters, and Patterns module in Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide for more information regarding regular expressions.

Step 3

notification linkupdown disable

Example:


RP/0/RSP0/CPU0:router(config-snmp-if-subset)# notification linkupdown disable

Disables linkUp and linkDown traps for all interfaces being configured. To enable previously disabled interfaces, use the no form of this command.

Step 4

commit

Step 5

(Optional) show snmp interface notification subset subset-number

Example:


RP/0/RSP0/CPU0:router# show snmp interface notification subset 10
 (Optional)

Displays the linkUp and linkDown notification status for all interfaces identified by the subset priority.

Step 6

(Optional) show snmp interface notification regular-expression expression

Example:


RP/0/RSP0/CPU0:router# show snmp interface notification 
    regular-expression "^Gig[a-zA-Z]+[0-9/]+\."
 (Optional)

Displays the linkUp and linkDown notification status for all interfaces identified by the regular expression.

Step 7

(Optional) show snmp interface notification type interface-path-id

Example:


RP/0/RSP0/CPU0:router# show snmp interface notification 
    tengige 0/4/0/3.10
 (Optional)

Displays the linkUp and linkDown notification status for the specified interface.

Configuration Examples for Implementing SNMP

Configuring SNMPv3: Examples

Setting an Engine ID

This example shows how to set the identification of the local SNMP engine: 


snmp-server engineID local 00:00:00:09:00:00:00:a1:61:6c:20:61

Note

After the engine ID has been configured, the SNMP agent restarts.

Verifying the Identification of the Local SNMP Engines

This example shows how to verify the identification of the local SNMP engine: 


config
  show snmp engineid
  
  SNMP engineID 00000009000000a1ffffffff

Creating a View

There are two ways to create a view:

  • You can include the object identifier (OID) of an ASN.1 subtree of a MIB family from a view by using the included keyword of the snmp-server view command.
  • You can exclude the OID subtree of the ASN.1 subtree of a MIB family from a view by using the excluded keyword of the snmp-server view command.

This example shows how to create a view that includes the sysName (1.3.6.1.2.1.1.5) object: 


config
  snmp-server view SNMP_VIEW1 1.3.6.1.2.1.1.5 included

This example shows how to create a view that includes all the OIDs of a system group: 


config
  snmp-server view SNMP_VIEW1 1.3.6.1.2.1.1 included

This example shows how to create a view that includes all the OIDs under the system group except the sysName object (1.3.6.1.2.1.1.5), which has been excluded: 


config
  snmp-server view SNMP_VIEW1 1.3.6.1.2.1.1 included
  snmp-server view SNMP_VIEW1 1.3.6.1.2.1.1.5 excluded

Verifying Configured Views

This example shows how to display information about the configured views: 


RP/0/RSP0/CPU0:router# show snmp view
  
  v1default 1.3.6.1 - included nonVolatile active 
  SNMP_VIEW1 1.3.6.1.2.1.1 - included nonVolatile active
  SNMP_VIEW1 1.3.6.1.2.1.1.5 - excluded nonVolatile active

Creating Groups

If you do not explicitly specify a notify, read, or write view, the Cisco IOS XR software uses the v1 default (1.3.6.1). This example shows how to create a group that utilizes the default view: 


RP/0/RSP0/CPU0:router(config)# snmp-server group group-name v3 auth

The following configuration example shows how to create a group that has read access to all the OIDs in the system except the sysUpTime object (1.3.6.1.2.1.1.3), which has been excluded from the view applied to the group, but write access only to the sysName object (1.3.6.1.2.1.1.5): 


!
  snmp-server view view_name1 1.3.6.1.2.1.1 included
  snmp-server view view_name1 1.3.6.1.2.1.1.3 excluded
  snmp-server view view_name2 1.3.6.1.2.1.1.5 included
  snmp-server group group_name1 v3 auth read view_name1 write view_name2
  !

Verifying Groups

This example shows how to verify the attributes of configured groups: 


RP/0/RSP0/CPU0:router# show snmp group
  
  groupname: group_name1                   security model:usm
  readview : view_name1                    writeview: view_name2
  notifyview: v1default
  row status: nonVolatile

Creating and Verifying Users

Given the following SNMPv3 view and SNMPv3 group configuration: 


!
  snmp-server view view_name 1.3.6.1.2.1.1 included
  snmp-server group group_name v3 noauth read view_name write view-name
  !

This example shows how to create a noAuthNoPriv user with read and write view access to a system group: 


config
  snmp-server user noauthuser group_name v3

Note

The user must belong to a noauth group before a noAuthNoPriv user can be created.

Only one remote host can be assigned to the same username for SNMP version 3. If you configure the same username with different remote hosts, only the last username and remote host combination will be accepted and will be seen in the show running configuration. In the case of multiple SNMP managers, multiple unique usernames are required.

This example shows the same username case which only the last configuration will be accepted:


snmp-server user username  nervectrgrp remote 10.69.236.146 udp-port 162 v3 auth sha <password> priv aes 128 <password>  
snmp-server user username  nervectrgrp remote 10.214.127.2 udp-port 162 v3 auth sha <password> priv aes 128  <password>
snmp-server user username  nervectrgrp remote 10.69.236.147 udp-port 162 v3 auth sha <password> priv aes 128 <password>
RP/0/RSP0/CPU0:router# show run snmp-server user
  
  snmp-server user username nervectrgrp remote 10.69.236.147 udp-port 162 v3 auth sha encrypted <password> priv aes 128 encrypted <password>

This example shows all 3 hosts for username1, username2, and username3 will be accepted.

:


snmp-server user username1  nervectrgrp remote 10.69.236.146 udp-port 162 v3 auth sha <password> priv aes 128 <password>  
snmp-server user username2  nervectrgrp remote 10.214.127.2 udp-port 162 v3 auth sha <password> priv aes 128  <password>
snmp-server user username3  nervectrgrp remote 10.69.236.147 udp-port 162 v3 auth sha <password> priv aes 128 <password>
RP/0/RSP0/CPU0:router# show run snmp-server user
  
  snmp-server user batmanusr1 nervectrgrp remote 10.69.236.146 udp-port 162 v3 auth sha encrypted <password> priv aes 128 encrypted <password>
  snmp-server user batmanusr2 nervectrgrp remote 10.214.127.2 udp-port 162 v3 auth sha encrypted <password> priv aes 128 encrypted <password>
  snmp-server user batmanusr3 nervectrgrp remote 10.69.236.147 udp-port 162 v3 auth sha encrypted <password> priv aes 128 encrypted <password>

This example shows how to verify the attributes that apply to the SNMP user: 


RP/0/RSP0/CPU0:router# show snmp user
  
  User name: noauthuser
  Engine ID: localSnmpID
  storage-type: nonvolatile active

Given the following SNMPv3 view and SNMPv3 group configuration: 


!
  snmp-server view SNMP_VIEW1 1.3.6.1.2.1.1 included
  snmp-server group SNMP_GROUP1 v3 auth notify SNMP_VIEW1 read SNMP_VIEW1 write SNMP_VIEW1
 !

This example shows how to create a user with authentication (including encryption), read, and write view access to a system group: 


config
  snmp-server user userv3authpriv SNMP_GROUP1 v3 auth md5 password123 priv aes 128 password123

Given the following SNMPv3 view and SNMPv3 group configuration: 


!
  snmp-server view view_name 1.3.6.1.2.1.1 included
  snmp group group_name v3 priv read view_name write view_name
  !

This example shows how to create authNoPriv user with read and write view access to a system group: 


RP/0/RSP0/CPU0:router(config)# snmp-server user authuser group_name v3 auth md5 clear auth_passwd

Note

Because the group is configured at a security level of Auth, the user must be configured as “auth” at a minimum to access this group (“priv” users could also access this group). The authNoPriv user configured in this group, authuser, must supply an authentication password to access the view. In the example, auth_passwd is set as the authentication password string. Note that clear keyword is specified before the auth_passwd password string. The clear keyword indicates that the password string being supplied is unencrypted.

This example shows how to verify the attributes that apply to SNMP user: 


RP/0/RSP0/CPU0:router# show snmp user
  
  User name: authuser
  Engine ID: localSnmpID
  storage-type: nonvolatile active

Given the following SNMPv3 view and SNMPv3 group configuration: 


!
  snmp view view_name 1.3.6.1.2.1.1 included
  snmp group group_name v3 priv read view_name write view_name
  !

This example shows how to create an authPriv user with read and write view access to a system group: 


config
  snmp-server user privuser group_name v3 auth md5 clear auth_passwd priv des56 clear priv_passwd

Note

Because the group has a security level of Priv, the user must be configured as a “priv” user to access this group. In this example, the user, privuser, must supply both an authentication password and privacy password to access the OIDs in the view.

This example shows how to verify the attributes that apply to the SNMP user: 


RP/0/RSP0/CPU0:router# show snmp user
  
  User name: privuser
  Engine ID: localSnmpID
  storage-type: nonvolatile active

Configuring Trap Notifications: Example

The following example configures an SNMP agent to send out different types of traps. The configuration includes a v2c user, a noAuthNoPriv user, anauthNoPriv user, and an AuthPriv user.


Note

The default User Datagram Protocol (UDP) port is 161. If you do not a specify a UDP port with the udp-port keyword and port argument, then the configured SNMP trap notifications are sent to port 161. 


!
  snmp-server host 10.50.32.170 version 2c userv2c udp-port 2345
  snmp-server host 10.50.32.170 version 3 auth userV3auth udp-port 2345
  snmp-server host 10.50.32.170 version 3 priv userV3priv udp-port 2345
  snmp-server host 10.50.32.170 version 3 noauth userV3noauth udp-port 2345
  snmp-server user userv2c groupv2c v2c 
  snmp-server user userV3auth groupV3auth v3 auth md5 encrypted 140F0A13 
  snmp-server user userV3priv groupV3priv v3 auth md5 encrypted 021E1C43 priv des56 encrypted 1110001C 
  snmp-server user userV3noauth groupV3noauth v3 LROwner
  snmp-server view view_name 1.3 included
  snmp-server community public RW 
  snmp-server group groupv2c v2c read view_name
  snmp-server group groupV3auth v3 auth read view_name
  snmp-server group groupV3priv v3 priv read view_name
  snmp-server group groupV3noauth v3 noauth read view_name
  !

This example shows how to verify the configuration SNMP trap notification recipients host, the recipients of SNMP trap notifications. The output displays the following information:

  • IP address of the configured notification host
  • UDP port where SNMP notification messages are sent
  • Type of trap configured
  • Security level of the configured user
  • Security model configured

config
  show snmp host
  
  Notification host: 10.50.32.170 udp-port: 2345 type: trap
  user: userV3auth security model: v3 auth
  
  Notification host: 10.50.32.170 udp-port: 2345 type: trap
  user: userV3noauth security model: v3 noauth
  
  Notification host: 10.50.32.170 udp-port: 2345 type: trap
  user: userV3priv security model: v3 priv
  
  Notification host: 10.50.32.170 udp-port: 2345 type: trap
  user: userv2c security model: v2c

Setting an IP Precedence Value for SNMP Traffic: Example

The following example shows how to set the SNMP IP Precedence value to 7:


configure
  snmp-server ipv4 precedence 7
  exit

  Uncommitted changes found, commit them before exiting(yes/no/cancel)? [cancel]: y

Setting an IP DSCP Value for SNMP Traffic: Example

The following example shows how to set the IP DSCP value of SNMP traffic to 45:


configure
  snmp-server ipv4 dscp 45
  exit

  Uncommitted changes found, commit them before exiting(yes/no/cancel)? [cancel]: y

Additional References

The following sections provide references related to Implementing SNMP on Cisco IOS XR software.

Related Documents

Related Topic

Document Title

Cisco IOS XR SNMP commands

SNMP Server Commands on the Cisco ASR 9000 Series Router module of System Management Command Reference for Cisco ASR 9000 Series Routers

MIB information

 Cisco ASR 9000 Series Aggregation Services Routers MIB Specifications Guide

Cisco IOS XR commands

Cisco ASR 9000 Series Aggregation Services Router Commands Master List

Getting started with Cisco IOS XR software

Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide

Information about user groups and task IDs

Configuring AAA Services on the Cisco ASR 9000 Series Router module of System Security Configuration Guide for Cisco ASR 9000 Series Routers

Cisco IOS XR Quality of Service

Modular QoS Configuration Guide for Cisco ASR 9000 Series Routers

Standards

Standards

Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

—

MIBs

MIBs

MIBs Link

—

To locate and download MIBs using Cisco IOS XR software, use the Cisco MIB Locator found at the following URL and choose a platform under the Cisco Access Products menu: http://cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

RFCs

RFCs

Title

RFC 3411

An Architecture for Describing Simple Network Management Protocol (SNMP) Management Frameworks

RFC 3412

Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)

RFC 3413

Simple Network Management Protocol (SNMP) 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)

RFC 3416

Version 2 of the Protocol Operations for the Simple Network Management Protocol (SNMP)

RFC 3417

Transport Mappings for the Simple Network Management Protocol (SNMP)

RFC 3418

Management Information Base (MIB) for the Simple Network Management Protocol (SNMP)

Technical Assistance

Description

Link

The Cisco Technical Support website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

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

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