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The Call Admission Control for IKE feature describes the application of Call Admission Control (CAC) to the Internet Key Exchange (IKE) protocol in Cisco IOS XE. CAC limits the number of simultaneous IKE security associations (SAs) (that is, calls to CAC) that a router can establish.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see 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 document.
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There are two ways to limit the number of IKE SAs that a router can establish to or from another router:
CAC is applied only to new SAs (that is, when an SA does not already exist between the peers). Every effort is made to preserve existing SAs. Only new SA requests will ever be denied due to a lack of system resources or because the configured IKE SA limit has been reached.
An SA is a description of how two or more entities will utilize security services to communicate securely on behalf of a particular data flow. IKE requires and uses SAs to identify the parameters of its connections. IKE can negotiate and establish its own SA. An IKE SA is used by IKE only, and it is bidirectional. An IKE SA cannot limit IPsec.
IKE drops SA requests based on a user-configured SA limit. To configure an IKE SA limit, enter the crypto call admission limit command. When there is a new SA request from a peer router, IKE determines if the number of active IKE SAs plus the number of SAs being negotiated meets or exceeds the configured SA limit. If the number is greater than or equal to the limit, the new SA request is rejected and a syslog is generated. This log contains the source destination IP address of the SA request.
A limit on the number of in-negotiation IKE connections can be configured. This type of IKE connection represents either an aggressive mode IKE SA or a main mode IKE SA prior to its authentication and actual establishment.
Using the crypto call admission limit ike in-negotiation-sa {number} command allows the configured number of in-negotiation IKE SAs to start negotiation without contributing to the maximum number of IKE SAs allowed.
CAC polls a global resource monitor so that IKE knows when the router is running short of CPU cycles or memory buffers. You can configure a limit, in the range to 100000, that represents the level of system resource usage in system resource usage units. When that level of resources is being used, IKE drops (will not accept new) SA requests. To configure the system resource usage limit, enter the call admission limit command.
For each incoming new SA request, the current load on the router is converted into a numerical value, representing the system resource usage level, and is compared to the resource limit set by the call admission limit command. If the current load is more than the configured resource limit, IKE drops the new SA request. Load on the router includes active SAs, CPU usage, and SA requests being considered.
The call admission load command configures a multiplier value from 0 to 1000 that represents a scaling factor for current system resource usage and a load metric poll rate of 1 to 32 seconds. The numerical value for the system resource usage level is calculated by the formula (scaling factor * current system resource usage) / 100. It is recommended that the call admission load command not be used unless advised by a Cisco Technical Assistance Center (TAC) engineer.
Perform this task to configure the absolute IKE SA limit. The router drops new IKE SA requests when the limit has been reached.
Perform this task to configure the system resource limit. The router drops new IKE SA requests when the level of system resources that are configured in the unit of charge is being used.
Command or Action | Purpose | |||
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Example: Router> enable |
Enables privileged EXEC mode.
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Example: Router# configure terminal |
Enters global configuration mode. |
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Example: Router(config)# call admission limit 1000 |
Sets the level of the system resources that, when used, causes IKE to stop accepting new SA requests.
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Example: Router(config)# exit |
Returns to privileged EXEC mode. |
To verify the CAC for IKE configuration, perform the following steps.
Step 1 | show call admission statistics Use this command to monitor the global CAC configuration parameters and the behavior of CAC. Example:
Router# show call admission statistics
Total Call admission charges: 82, limit 1000
Total calls rejected 1430, accepted 0
Load metric: charge 82, unscaled 82%
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Step 2 | show crypto call admission statistics Use this command to monitor crypto CAC statistics. Example:
Router# show crypto call admission statistics
---------------------------------------------------------------------
Crypto Call Admission Control Statistics
---------------------------------------------------------------------
System Resource Limit: 90 Max IKE SAs: 0 Max in nego: 25
Total IKE SA Count: 359 active: 338 negotiating: 21
Incoming IKE Requests: 1297 accepted: 166 rejected: 1131
Outgoing IKE Requests: 1771 accepted: 195 rejected: 1576
Rejected IKE Requests: 2707 rsrc low: 1314 SA limit: 1393
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The following example shows how to specify that there can be a maximum of 25 SAs before IKE starts rejecting new SA requests:
Router(config)# crypto call admission limit ike sa 25
The following example shows how to specify that IKE should drop SA requests when the level of system resources that are configured in the unit of charge reaches 9000:
Router(config)# call admission limit 9000
The following sections provide references related to Call Admission Control for IKE.
Related Topic |
Document Title |
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Cisco IOS commands |
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Configuring IKE |
Configuring Internet Key Exchange for IPsec VPNs |
IKE commands |
Cisco IOS Security Command Reference |
Standards |
Title |
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None |
-- |
MIBs |
MIBs Link |
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No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs |
Title |
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RFC 2409 |
The Internet Key Exchange |
Description |
Link |
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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. |
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 1 | Feature Information for Call Admission Control for IKE |
Feature Name |
Releases |
Feature Information |
---|---|---|
Call Admission Control for IKE |
Cisco IOS XE Release 2.1 |
The Call Admission Control for IKE feature describes the application of Call Admission Control (CAC) to the Internet Key Exchange (IKE) protocol in Cisco IOS XE. CAC limits the number of simultaneous IKE security associations (SAs) (that is, calls to CAC) that a router can establish. The following commands were introduced or modified: call admission limit, clear crypto call admission statistics, crypto call admission limit, show call admission statistics, show crypto call admission statistics. |
Ability to Configure a Limit on the Number of In-negotiation IKE Connections |
Cisco IOS XE Release 2.1 |
This feature was implemented on the Cisco ASR 1000 Series Routers. The following command was introduced or modified: crypto call admission limit. |
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