Table Of Contents
DHCP Server MIB
Contents
Prerequisites for the DHCP Server MIB
Information About the DHCP Server MIB
SNMP Overview
DHCP Server Trap Notifications
Tables and Objects in the DHCP Server MIB
How to Enable DHCP Trap Notifications
Configuring the Router to Send SNMP Trap Notifications About DHCP
Troubleshooting Tips
Configuration Examples for the DHCP Server MIB
DHCP Server MIB—Secondary Subnet Trap: Example
DHCP Server MIB—Address Pool Trap: Example
DHCP Server MIB—Lease Limit Violation Trap: Example
Additional References
Related Documents
Standards
MIBs
RFCs
Technical Assistance
Feature Information for DHCP Server MIB
DHCP Server MIB
First Published: December 31, 2007
Last Updated: December 31, 2007
The DHCP Server MIB feature provides Simple Network Management Protocol (SNMP) access to and control of Cisco IOS Dynamic Host Configuration Protocol (DHCP) server software on a Cisco router by an external network management device.
Finding Feature Information in This Module
Your Cisco IOS software release may not support all of the features documented in this module. For the latest feature information and caveats, see the release notes for your Cisco IOS software release. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for DHCP Server MIB" section.
Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Contents
•
Prerequisites for the DHCP Server MIB
•Information About the DHCP Server MIB
•How to Enable DHCP Trap Notifications
•Configuration Examples for the DHCP Server MIB
•Additional References
•Feature Information for DHCP Server MIB
Prerequisites for the DHCP Server MIB
SNMP must be enabled on the router before DHCP server trap notifications can be configured.
Information About the DHCP Server MIB
To implement the DHCP Server MIB feature, you should understand the following concepts:
•SNMP Overview
•DHCP Server Trap Notifications
•Tables and Objects in the DHCP Server MIB
SNMP Overview
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 that is used for monitoring and managing devices in a network.
SNMP defines two main types of entities: managers and agents. The SNMP manager is a system that controls and monitors the activities of network hosts using SNMP. The agent is the software component within a remote networking device that maintains the data and reports this data, as needed, to the manager. The manager and agent share a Management Information Base (MIB) that defines the information that the agent can make available to the manager.
An important feature of SNMP is the capability to generate unsolicited notifications from an SNMP agent. These trap notifications are messages alerting the SNMP manager to conditions on the network. Traps are considered an agent-to-manager function and a request for confirmation of receipt from the SNMP manager is not required.
DHCP Server Trap Notifications
DHCP server trap notifications are sent to the SNMP manager for the following events:
•Address utilization for a subnet has risen above or fallen below a configurable threshold.
•Address utilization for an address pool has risen above or fallen below a configurable threshold.
•A lease limit violation is detected. The lease limit configuration allows you to control the number of subscribers per interface.
•The DHCP server has started or stopped.
•A duplicate IP address is detected.
The DHCP Server MIB feature does not send the same type of trap notification back-to-back for the same threshold event. For example, if the low threshold value for available free addresses becomes equal to or less than the configured value, a free address low event trap notification on the subnet or pool is generated. This same trap notification will not be resent until the value for the available free addresses has exceeded the value of the free high threshold and vise versa. This threshold control mechanism applies to all trap notifications concerning thresholds in addition to the trap notifications for the DHCP server start and stop time and the lease limit violation. The duplicate IP address trap notification is not subject to this threshold control mechanism.
Tables and Objects in the DHCP Server MIB
The DHCP Server MIB consists of the following tables and objects. The first character of a row in the table begins with "c" (Cisco) and is mapped to the object defined in the IETF draft RFC, Dynamic Host Configuration Protocol for IPv4 Server MIB. If the information is not currently available in Cisco IOS software, the value in the second column is displayed as 0 (zero).
•cDhcpv4SrvSystemsObjects (see Table 1)—System description and object IDs
•cBootpHCCounterObjects (see Table 2)—BOOTP counter information
•cDhcpv4HCCounterObjects (see Table 3)—DHCPv4 counter information
•cDhcpv4ServerSharedNetTable (see Table 4)—DHCP address pool information
•cDhcpv4ServerSubnetTable (see Table 5)—Additional DHCP address pool subnet information including secondary subnet information
•cDhcpv4SrvExtSubnetTable (see Table 6)—Additional DHCP address pool subnet information
•cDhcpv4ServerNotifyObjectsGroup (see Table 7)—This objects group is used by the cDhcpv4ServerNotificationsGroup notifications group.
•cDhcpv4ServerNotificationsGroup (see Table 8)—This notifications group consists of all traps defined in the Cisco IOS DHCP server.
•cDhcpv4SrvExtNotifyGroup (see Table 9)—This notifications group consists of all traps not defined in the draft DHCPv4 Server MIB RFC.
Table 1 cDhcpv4SrvSystemsObjects and Descriptions
Name
|
Description
|
cDhcpv4SrvSystemDescr
|
Contains a textual description of the server (full name and version identification).
|
cDhcpv4SrvSystemObjectID
|
Cisco experiment node for the DHCP Server MIB.
For example, 1.3.6.1.4.1.9.10.102...
|
Table 2 cBootpHCCounterObjects and Descriptions
Name
|
Description
|
cBootpHCCountRequests
|
The number of packets received that do contain a BOOTREQUEST message type in the first octet.
|
cBootpHCCountInvalids
|
0
|
cBootpHCCountReplies
|
The number of packets received that contain a BOOTREPLY message type in the first octet.
|
cBootpHCCountDroppedUnknown Clients
|
0
|
cBootpHCCountDroppedNotServingSubnet
|
0
|
Table 3 cDhcpv4HCCounterObjects and Descriptions
Name
|
Description
|
cDhcpv4HCCountDiscovers
|
The number of DHCPDISCOVER packets received.
|
cDhcpv4HCCountOffers
|
The number of DHCPOFFER packets sent.
|
cDhcpv4HCCountRequests
|
The number of DHCPREQUEST packets sent.
|
cDhcpv4HCCountDeclines
|
The number of DHCPDECLINE packets sent.
|
cDhcpv4HCCountAcks
|
The number of DHCPACK packets sent.
|
cDhcpv4HCCountNaks
|
The number of DHCPNACK packets sent.
|
cDhcpv4HCCountReleases
|
The number of DHCPRELEASE packets sent.
|
cDhcpv4HCCountInforms
|
The number of DHCPINFORM packets sent.
|
cDhcpv4HCCountForcedRenews
|
0
|
cDhcpv4HCCountInvalids
|
The number of DHCP packets received whose DHCP message type is not understood or handled by the DHCP server.
|
cDhcpv4HCCountDropUnknownClient
|
0
|
cDhcpv4HCCountDropNotServingSubnet
|
0
|
Table 4 cDhcpv4ServerSharedNetTable and Descriptions
Name
|
Description
|
cDhcpv4ServerSharedNetName
|
The DHCP address pool name.
|
cDhcpv4ServerSharedNetFreeAddr
LowThreshold
|
This entry value corresponds to the utilization mark high command in DHCP pool configuration mode multiplied by the total pool addresses then divided by 100.
|
cDhcpv4ServerSharedNetFreeAddrHighThreshold
|
This entry value corresponds to the utilization mark low command in DHCP pool configuration mode multiplied by the total subnet addresses then divided by 100.
|
cDhcpv4ServerSharedNetFree
Addresses
|
The number of IPv4 addresses that are available within this shared network.
|
cDhcpv4ServerSharedNetReserved
Addresses
|
The number of IP addresses that are reserved for the pool (not available for assignment). This entry corresponds to the ip dhcp excluded-address global configuration command. The value is zero if no excluded addresses are defined for the pool.
|
cDhcpv4ServerSharedNetTotal
Addresses
|
The number of IP addresses that are available within this shared network.
|
Table 5 cDhcpv4ServerSubnetTable and Descriptions
Name
|
Description
|
cDhcpv4ServerSubnetAddress
|
The IP address of the subnet entry in the table.
|
cDhcpv4ServerSubnetMask
|
The subnet mask of the subnet.
|
cDhcpv4ServerSubnetSharedNetworkName
|
The DHCP address pool name to which the subnet belongs.
|
cDhcpv4ServerSubnetFreeAddrLowThreshold
|
This entry value corresponds to the override utilization high command in DHCP pool secondary subnet configuration mode multiplied by the total subnet addresses then divided by 100.
|
cDhcpv4ServerSubnetFreeAddrHighThreshold
|
This entry value corresponds to the override utilization low command in DHCP pool secondary subnet configuration mode multiplied by the total subnet addresses then divided by 100.
|
cDhcpv4ServerSubnetFree
Addresses
|
The number of free IP addresses that are available in the subnet.
|
Table 6 cDhcpv4SrvExtSubnetTable and Descriptions
Name
|
Description
|
cDhcpv4ServerDefaultRouterAddress
|
The entry corresponds to the override default-router command in DHCP pool secondary subnet configuration mode.
|
cDhcpv4ServerSubnetStartAddress
|
The first subnet IP address.
|
cDhcpv4ServerSubnetEndAddress
|
The last subnet IP address.
|
Table 7 cDhcpv4ServerNotifyObjectsGroups and Descriptions
Name
|
Description
|
cDhcpv4ServerNotifyDuplicateIpAddr
|
The IP address is found to be a duplicate. Duplicates are detected by servers who send a PING before offering an IP address lease or by a client sending a gratuitous ARP message reported through a DHCPDECLINE message.
|
cDhcpv4ServerNotifyDuplicateMac
|
The offending MAC address that caused a duplicate IPv4 address to be detected, if captured by the server, otherwise set to 00-00-00-00-00-00.
|
cDhcpv4ServerNotifyClientOrServerDetected
|
This object is set by the server to client if the client used DHCPDECLINE to mark the offered address as in use, or to server if the server discovered that address was in use by a client before offering it.
|
cDhcpv4ServerNotifyServerStart
|
The date and time when the server began operation, which is controlled by the service dhcp command.
|
cDhcpv4ServerNotifyServerStop
|
The date and time when the server ceased operation, which is controlled by no service dhcp command.
|
Table 8 cDhcpv4ServerNotificationsGroup and Descriptions
Name
|
Description
|
cDhcpv4ServerFreeAddressLow
|
This notification signifies that the number of available IP addresses for a DHCP address pool has fallen below the defined low threshold. This notification corresponds to the snmp-server enable traps dhcp global configuration command.
|
cDhcpv4ServerFreeAddressHigh
|
This notification signifies that the number of available IP addresses for a DHCP address pool has risen above the defined high threshold. This notification corresponds to the snmp-server enable traps dhcp global configuration command.
|
cDhcpv4ServerStartTime
|
This notification signifies that the server has started. This notification corresponds to the service dhcp and snmp-server enable traps dhcp time global configuration commands.
|
cDhcpv4ServerStopTime
|
This notification signifies that the server has stopped normally. This notification corresponds to the no service dhcp and snmp-server enable traps dhcp time global configuration commands.
|
cDhcpv4ServerDuplicateAddress
|
This notification signifies that a duplicate IP address has been detected. This notification corresponds to the snmp-server enable traps dhcp duplicate global configuration command.
|
Table 9 cDhcpv4SrvNotifyGroup and Descriptions
Name (not in the RFC draft)
|
Description
|
cDhcpv4ServerIfLeaseLimitExceeded
|
This notification signifies that a per interface lease limit is exceeded. This notification corresponds to the snmp-server enable traps dhcp interface global configuration command.
|
cDhcpv4ServerSubnetFreeAddressLow
|
This notification signifies that the number of available IP addresses for a subnet has fallen below the defined low threshold. This notification corresponds to the snmp-server enable traps dhcp subnet global configuration command.
|
cDhcpv4ServerSubnetFreeAddressHigh
|
This notification signifies that the number of available IPv4 addresses for a subnet has risen above the defined high threshold. This notification corresponds to the snmp-server enable traps dhcp subnet global configuration command.
|
How to Enable DHCP Trap Notifications
Perform the following task to enable the router to send trap notifications about DHCP.
•Configuring the Router to Send SNMP Trap Notifications About DHCP
Configuring the Router to Send SNMP Trap Notifications About DHCP
DHCP trap notifications are disabled by default. The trap notification is disabled if the corresponding trap configuration is not enabled.
SUMMARY STEPS
1. enable
2. configure terminal
3. snmp-server enable traps dhcp [duplicate] [interface] [pool] [subnet] [time]
4. end
DETAILED STEPS
| |
Command or Action
|
Purpose
|
Step 1
|
enable
Example:
Router> enable
|
Enables privileged EXEC mode.
•Enter your password if prompted.
|
Step 2
|
configure terminal
Example:
Router# configure terminal
|
Enters global configuration mode.
|
Step 3
|
snmp-server enable traps dhcp [duplicate]
[interface] [pool] [subnet] [time]
Example:
Router(config)# snmp-server enable traps dhcp
|
Enables the sending of DHCP SNMP trap notifications.
•duplicate—Sends notification about duplicate IP addresses.
•interface—Sends notification that a per interface lease limit is exceeded.
•pool—Sends notification when address utilization for an address pool has risen above or fallen below a configurable threshold.
•subnet—Sends notification when address utilization for a subnet has risen above or fallen below a configurable threshold.
•time—Sends notification that the DHCP server has started or stopped.
•If you specify the snmp-server enables traps dhcp command without any of the optional keywords, all DHCP trap notifications are enabled.
|
Step 4
|
end
Example:
Router(config)# end
|
Returns the router to privileged EXEC mode.
|
Troubleshooting Tips
You can troubleshoot DHCP server SNMP events by using the debug ip dhcp server snmp privileged EXEC command.
Configuration Examples for the DHCP Server MIB
This section provides the following configuration examples:
•DHCP Server MIB—Secondary Subnet Trap: Example
•DHCP Server MIB—Address Pool Trap: Example
•DHCP Server MIB—Lease Limit Violation Trap: Example
DHCP Server MIB—Secondary Subnet Trap: Example
The following example configures 192.0.2.0/24 as the subnetwork number and mask of the DHCP pool named pool2 and then adds the DHCP pool secondary subnet specified by the subnet number and mask 192.0.4.0/30. The IP addresses in pool2 consist of two disjoint subnets: the addresses from 192.0.2.1 to 192.0.2.254 and the addresses from 192.0.4.1 to 192.0.4.2.
The address pool utilization mark, configured at the global level, will be overridden at the secondary subnet level. A trap is sent to the SNMP manager if the subnet size of the secondary subnet exceeds or goes below the level specified by the override utilization commands.
The utilization mark {high | low}log command enables a system message to be generated for a DHCP address pool or secondary subnet when the utilization exceeds the configured high utilization threshold or falls below the configured low utilization threshold.
utilization mark high 80 log
utilization mark low 70 log
network 192.0.2.0 255.255.255.0
network 192.0.4.0 255.255.255.252 secondary
override utilization high 40
override utilization low 30
snmp-server enable traps dhcp subnet
DHCP Server MIB—Address Pool Trap: Example
In the following example, if the address utilization exceeds the high threshold or drops below the low threshold, an SNMP trap will be sent to the SNMP manager and a system message will be generated.
utilization mark high 80 log
utilization mark low 70 log
snmp-server enable traps dhcp pool
DHCP Server MIB—Lease Limit Violation Trap: Example
In the following example, four DHCP clients are allowed to receive IP addresses. If a fifth client tries to obtain an IP address, the DHCPDISCOVER messages will not be forwarded to the DHCP server and a trap will be sent to the SNMP manager.
snmp-server enable traps dhcp interface
Additional References
The following sections provide references related to the DHCP Server MIB feature.
Related Documents
Standards
Standard
|
Title
|
No new or modified standards are supported by this feature.
|
—
|
MIBs
MIB
|
MIBs Link
|
•CISCO-IETF-DHCP-SERVER-MIB
•CISCO-IETF-DHCP-SERVER-EXT-MIB
|
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
http://www.cisco.com/go/mibs
|
RFCs
Technical Assistance
Description
|
Link
|
The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.
To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.
Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.
|
http://www.cisco.com/techsupport
|
Feature Information for DHCP Server MIB
Table 10 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Release 12.2(1) or a later release appear in the table.
Not all commands may be available in your Cisco IOS software release. For details on when support for a specific command was introduced, see the command reference documentation.
For information on a feature in this technology that is not documented here, see the "DHCP Features Roadmap".
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 10 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.
Table 10 Feature Information for DHCP Server MIB
Feature Name
|
Releases
|
Feature Information
|
DHCP Server MIB
|
12.2(33)SRC
|
The DHCP Server MIB feature provides SNMP access to and control of Cisco IOS DHCP server software on a Cisco router by an external network management device.
The following commands were introduced by this feature: snmp-server enable traps dhcp and debug ip dhcp server snmp.
|
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2007 Cisco Systems, Inc. All rights reserved.
