 Feedback
|
Table Of Contents
OSPF Update Packet-Pacing Configurable Timers
Related Features and Technologies
Supported Standards, MIBs, and RFCs
Configuring OSPF Packet-Pacing Timers
Verifying OSPF Packet-Pacing Timers
Monitoring and Maintaining OSPF Packet-Pacing Timers
OSPF Update Packet-Pacing Configurable Timers
Feature History
This feature module describes the OSPF Update Packet-Pacing Configurable Timers feature. It includes the following sections:
•
Related Features and Technologies
•
•
Feature Overview
In rare situations, you might need to change Open Shortest Path First (OSPF) packet-pacing default timers to mitigate CPU or buffer utilization issues associated with flooding very large numbers of link-state advertisements (LSAs). The OSPF Update Packet-Pacing Configurable Timers feature allows you to configure the rate at which OSPF LSA flood pacing, retransmission pacing, and group pacing updates occur.
Configuring OSPF flood pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF transmission queue. Configuring OSPF retransmission pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF retransmission queue. Cisco IOS software groups the periodic refresh of LSAs to improve the LSA packing density for the refreshes in large topologies. The group timer controls the interval used for group LSA refreshment; however, this timer does not change the frequency that individual LSAs are refreshed (the default refresh occurs every 30 minutes).
Note
Benefits
The OSPF Update Packet-Pacing Configurable Timers feature provides the administrator with a mechanism to control the rate at which LSA updates occur in order to reduce high CPU or buffer utilization that can occur when an area is flooded with a very large number of LSAs.
Restrictions
Do not change the packet pacing timers unless all other options to meet OSPF packet flooding requirements have been exhausted. Specifically, network operators should prefer summarization, stub area usage, queue tuning, and buffer tuning before changing the default timers. Furthermore, there are no guidelines for changing timer values; each OSPF deployment is unique and should be considered on a case-by-case basis. The network operator assumes risks associated with changing the default timer values.
Related Features and Technologies
The OSPF Update Packet-Pacing Configurable Timers feature is an extension of the OSPF routing protocol. For more information about configuring OSPF, packet pacing, area border router (ABR) and autonomous system boundary router (ASBR) summarization, and stub router configuration, refer to the Release 12.2 Cisco IOS IP Routing Configuration Guide and the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols.
Supported Platforms
The OSPF Update Packet-Pacing Configurable Timers feature is supported by the following platforms in Cisco IOS Release 12.2(14)S that support OSPF:
•
•
•
Determining Platform Support Through Cisco Feature Navigator
Cisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.
Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.
To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register.
Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:
Availability of Cisco IOS Software Images
Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator.
Supported Standards, MIBs, and RFCs
Standards
No new or modified standards are supported by this feature.
MIBs
No new or modified MIBs are supported by this feature.
To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:
http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml
RFCs
No new or modified RFCs are supported by this feature.
Configuration Tasks
See the following sections for configuration tasks for the OSPF Update Packet-Pacing Configurable Timers feature. Each task in the list is identified as either required or optional:
•
•
Configuring OSPF Packet-Pacing Timers
To configure a flood packet pacing timer, use the following commands beginning in router configuration mode:
To configure a retransmission packet pacing timer, use the following commands beginning in router configuration mode:
To configure a group packet pacing timer, use the following commands beginning in router configuration mode:
Verifying OSPF Packet-Pacing Timers
To verify that OSPF packet pacing has been configured, use the show ip ospf privileged EXEC command. The output of the show ip ospf command will display the type and delay time of the configurable pacing timers (flood, retransmission, group). The following example output is from the show ip ospf command:
Router# show ip ospfRouting Process "ospf 1" with ID 10.0.0.1 and Domain ID 10.20.0.1Supports only single TOS(TOS0) routesSupports opaque LSASPF schedule delay 5 secs, Hold time between two SPFs 10 secsMinimum LSA interval 5 secs. Minimum LSA arrival 1 secsLSA group pacing timer 100 secsInterface flood pacing timer 55 msecsRetransmission pacing timer 100 msecsNumber of external LSA 0. Checksum Sum 0x0Number of opaque AS LSA 0. Checksum Sum 0x0Number of DCbitless external and opaque AS LSA 0Number of DoNotAge external and opaque AS LSA 0Number of areas in this router is 2. 2 normal 0 stub 0 nssaExternal flood list length 0Area BACKBONE(0)Number of interfaces in this area is 2Area has message digest authenticationSPF algorithm executed 4 timesArea ranges areNumber of LSA 4. Checksum Sum 0x29BEBNumber of opaque link LSA 0. Checksum Sum 0x0Number of DCbitless LSA 3Number of indication LSA 0Number of DoNotAge LSA 0Flood list length 0Area 172.16.26.0Number of interfaces in this area is 0Area has no authenticationSPF algorithm executed 1 timesArea ranges are192.168.0.0/16 Passive AdvertiseNumber of LSA 1. Checksum Sum 0x44FDNumber of opaque link LSA 0. Checksum Sum 0x0Number of DCbitless LSA 1Number of indication LSA 1Number of DoNotAge LSA 0Flood list length 0Troubleshooting Tips
If the number of OSPF packet retransmissions rapidly increases, increase the value of the packet pacing timers. The number of OSPF packet retransmissions is displayed in the output of the show ip ospf neighbor command.
Monitoring and Maintaining OSPF Packet-Pacing Timers
To monitor and maintain OSPF packet-pacing timers, use the following commands in privileged EXEC mode:
Configuration Examples
This section provides the following configuration examples:
•
Flood Pacing Example
The following example configures LSA flood pacing updates to occur in 50-millisecond intervals for OSPF routing process 1:
Router(config)# router ospf 1Router(config-router)# timers pacing flood 50Retransmission Pacing Example
The following example configures LSA flood pacing updates to occur in 100-millisecond intervals for OSPF routing process 1:
Router(config)# router ospf 1Router(config-router)# timers pacing retransmission 100Group Pacing Example
The following example configures OSPF group pacing updates between LSA groups to occur in 75-second intervals for OSPF routing process 1:
Router(config)# router ospf 1Router(config-router)# timers pacing lsa-group 75Command Reference
This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.
New Commands
Modified Commands
timers pacing flood
To configure link-state advertisement (LSA) flood packet pacing, use the timers pacing flood command in router configuration mode. To restore the default flood packet pacing value, use the no form of this command.
timers pacing flood milliseconds
no timers pacing flood
Syntax Description
Defaults
33 milliseconds
Command Modes
Router configuration
Command History
12.2(4)T
This command was introduced.
12.2(14)S
This command was integrated into Cisco IOS Release 12.2(14)S.
Usage Guidelines
Configuring Open Shortest Path First (OSPF) flood pacing timers allows you to control interpacket spacing between consecutive link-state update packets in the OSPF transmission queue. This command allows you to control the rate at which LSA updates occur so that high CPU or buffer utilization that can occur when an area is flooded with a very large number of LSAs can be reduced.
The default settings for OSPF packet pacing timers are suitable for the majority of OSPF deployments. Do not change the packet pacing timers unless all other options to meet OSPF packet flooding requirements have been exhausted. Specifically, network operators should prefer summarization, stub area usage, queue tuning, and buffer tuning before changing the default flood timers. Furthermore, there are no guidelines for changing timer values; each OSPF deployment is unique and should be considered on a case-by-case basis. The network operator assumes risks associated with changing the default flood timer values.
Examples
The following example configures LSA flood packet-pacing updates to occur in 55-millisecond intervals for OSPF routing process 1:
Router(config)# router ospf 1Router(config-router)# timers pacing flood 55Related Commands
timers pacing lsa-group
To change the interval at which Open Shortest Path First (OSPF) link-state advertisements (LSAs) are collected into a group and refreshed, checksummed, or aged, use the timers pacing lsa-group command in router configuration mode. To restore the default value, use the no form of this command.
timers pacing lsa-group seconds
no timers pacing lsa-group
Syntax Description
seconds
Number of seconds in the interval at which LSAs are grouped and refreshed, checksummed, or aged. The range is from 10 to 1800 seconds. The default value is 240 seconds.
Defaults
The default interval for this command is 240 seconds. OSPF LSA group pacing is enabled by default.
Command Modes
Router configuration
Command History
Usage Guidelines
This command allows you to control the rate at which LSA updates occur so that high CPU or buffer utilization that can occur when an area is flooded with a very large number of LSAs can be reduced. The default settings for OSPF packet pacing timers are suitable for the majority of OSPF deployments. Do not change the packet pacing timers unless all other options to meet OSPF packet flooding requirements have been exhausted. Specifically, network operators should prefer summarization, stub area usage, queue tuning, and buffer tuning before changing the default flooding timers. Furthermore, there are no guidelines for changing timer values; each OSPF deployment is unique and should be considered on a case-by-case basis. The network operator assumes the risks associated with changing the default timer values.
Cisco IOS software groups the periodic refresh of LSAs to improve the LSA packing density for the refreshes in large topologies. The group timer controls the interval used for group refreshment of LSAs; however, this timer does not change the frequency that individual LSAs are refreshed (the default refresh rate is every 30 minutes).
The duration of the LSA group pacing is inversely proportional to the number of LSAs the router is handling. For example, if you have about 10,000 LSAs, decreasing the pacing interval would benefit you. If you have a very small database (40 to 100 LSAs), increasing the pacing interval to 10 to 20 minutes might benefit you slightly.
Examples
The following example configures OSPF group packet-pacing updates between LSA groups to occur in 60-second intervals for OSPF routing process 1:
Router(config)# router ospf 1Router(config-router)# timers pacing lsa-group 60Related Commands
Displays general information about OSPF routing processes.
Configures LSA flood packet pacing.
Configures LSA retransmission packet pacing.
timers pacing retransmission
To configure link-state advertisement (LSA) retransmission packet pacing, use the timers pacing retransmission command in router configuration mode. To restore the default retransmission packet pacing value, use the no form of this command.
timers pacing retransmission milliseconds
no timers pacing retransmission
Syntax Description
milliseconds
The time (in milliseconds) at which LSAs in the retransmission queue are paced. The configurable range is from 5 milliseconds to 200 milliseconds. The default value is 66 milliseconds.
Defaults
66 milliseconds
Command Modes
Router configuration
Command History
12.2(4)T
This command was introduced.
12.2(14)S
This command was integrated into Cisco IOS Release 12.2(14)S.
Usage Guidelines
Configuring OSPF retransmission pacing timers allow you to control interpacket spacing between consecutive link-state update packets in the OSPF retransmission queue. This command allows you to control the rate at which LSA updates occur so that high CPU or buffer utilization that can occur when an area is flooded with a very large number of LSAs can be reduced. The default settings for OSPF packet retransmission pacing timers are suitable for the majority of OSPF deployments. Do not change the packet retransmission pacing timers unless all other options to meet OSPF packet flooding requirements have been exhausted. Specifically, network operators should prefer summarization, stub area usage, queue tuning, and buffer tuning before changing the default flooding timers. Furthermore, there are no guidelines for changing timer values; each OSPF deployment is unique and should be considered on a case-by-case basis. The network operator assumes risks associated with changing the default packet retransmission pacing timer values.
Examples
The following example configures LSA flood pacing updates to occur in 55-millisecond intervals for OSPF routing process 1:
Router(config)# router ospf 1Router(config-router)# timers pacing flood 55Related Commands
show ip ospf
To display general information about Open Shortest Path First (OSPF) routing processes, use the show ip ospf command in privileged EXEC mode.
show ip ospf [process-id]
Syntax Description
process-id
(Optional) Process ID. If this argument is included, only information for the specified routing process is included.
Command Modes
privileged EXEC
Command History
Examples
The following is sample output from the show ip ospf command when entered without a specific OSPF process ID:
Router# show ip ospfRouting Process "ospf 201" with ID 10.0.0.1 and Domain ID 10.20.0.1Supports only single TOS(TOS0) routesSupports opaque LSASPF schedule delay 5 secs, Hold time between two SPFs 10 secsMinimum LSA interval 5 secs. Minimum LSA arrival 1 secsLSA group pacing timer 100 secsInterface flood pacing timer 55 msecsRetransmission pacing timer 100 msecsNumber of external LSA 0. Checksum Sum 0x0Number of opaque AS LSA 0. Checksum Sum 0x0Number of DCbitless external and opaque AS LSA 0Number of DoNotAge external and opaque AS LSA 0Number of areas in this router is 2. 2 normal 0 stub 0 nssaExternal flood list length 0Area BACKBONE(0)Number of interfaces in this area is 2Area has message digest authenticationSPF algorithm executed 4 timesArea ranges areNumber of LSA 4. Checksum Sum 0x29BEBNumber of opaque link LSA 0. Checksum Sum 0x0Number of DCbitless LSA 3Number of indication LSA 0Number of DoNotAge LSA 0Flood list length 0Area 172.16.26.0Number of interfaces in this area is 0Area has no authenticationSPF algorithm executed 1 timesArea ranges are192.168.0.0/16 Passive AdvertiseNumber of LSA 1. Checksum Sum 0x44FDNumber of opaque link LSA 0. Checksum Sum 0x0Number of DCbitless LSA 1Number of indication LSA 1Number of DoNotAge LSA 0Flood list length 0Table 1 describes the significant fields shown in the display.
