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Introduction
This chapter describes the ability to take a fabric link down after a configurable number of fabric down events occur over a set period of time.
The Avici router is architected such that the active portion of the switch fabric is incorporated into each routing module. Each routing module consists of a switch card coupled with one of several types of line interface cards. The switch card is common to all Avici router routing modules.
The switch fabric version on all systems is Version 2. For currently supported systems, fabric version configuration serves no purpose. Ignore the fabric-version command.
Controlling Fabric Down Events
A link bounce is an established fabric link that goes into a down state followed by a re-establishing of the link. Persistent link bounce is undesirable in a fabric. Some events that cause a link down-event are:
- Module failure
- CRC error discovered on the fabric link
- An uncontrolled module reboot
IPriori supports a Heuristic Link Transition Filter (HLTF). HLTF allows you to set, for each fabric axis, the number of allowable down events that can occur within a time window, before the link is permanently taken down. There are six link axes: plus and minus x, y, and z. If the number of current link down-events match the threshold set for that link's axis type, within the set time period, the link will be brought down and stay down until you reset the heuristic for that link, or the server reboots.
IPriori also supports the enabling and disabling of HLTF globally across the Avici router.
Understanding the Fabric Down-event Threshold and Time-Window
The Heuristic Link Transition Filter determines whether a link should be taken down permanently based upon two values: the down-event threshold and the time-window period. The down-event threshold is the maximum number of down-events that can occur on a given link before the fabric link is permanently taken down. The time-window period has two functions: it first plays a role in how much time passes before a down-event is dropped from the current down-event queue and secondly if during any time-window period the down-event threshold for a given link is reached, the link is administratively brought down.
The down-event threshold default is set to 10. The time-window period default is set to 10 minutes.
Each time a down-event occurs it is time stamped and placed in the current down-event queue. For example, when the link first comes up, there are no down-events in the down-event queue. When a link down-event occurs, this event is time-stamped and placed in the down-event queue. Assuming the default time-window period of 10 minutes and no other down-events occur, at the end of 10 minutes the down-event is removed from the down-event queue which is once again empty. If during any 10 minute period, the number of down-events remaining in the current down-events queue should equal the down-events threshold, the link is administratively taken down.
Changing the Down-event Threshold
You can change the down-event threshold for all link axes or a specific axis for this module using the fabric link down-event command in module configuration mode. You specify whether the change affects a specific axis or all axes, as well as the new down-event threshold value.
NOTE It is strongly recommended that you do not change the down-event threshold default values unless you are certain you know what you are doing. The unnecessary taking down of too many links can result in lost system forwarding performance.
Example: The following example changes the down-event threshold value for the x-plus axis to 7 for module 1/5:
router#config terminal
Enter configuration commands, one per line. End with CNTL/Z.
router(config)#module 1/5
router(config-module)#fabric link down-event xplus 7
router(config-module)#end
Changing the Time-window Period
You can change the time-window period for all axes or a specific axis for this module using the fabric link time-window command in module configuration mode. You specify whether the change affects a specific axis or all axes, as well as the new time-window period value.
NOTE It is strongly recommended that you do not change the time-window period default values unless you are certain you know what you are doing. The unnecessary taking down of too many links can result in lost system forwarding performance.
Example: The following example changes the time-window period value for all x-plus axes to 12 minutes for module 1/5:
router#config terminal
Enter configuration commands, one per line. End with CNTL/Z.
router(config)#module 1/5
router(config-module)#fabric link time-window xplus 12
router(config-module)#end
Disabling the Heuristic Link Transition Filter (HLTF)
If you do not want fabric links dynamically brought down using HLTF, you can disable HLTF using the fabric link heuristic shutdown command in configuration command mode. You can re-enable HLTF using the no option with this command.
Example: The following example disables the heuristic link transition filter for this Avici router:
router#config terminal
Enter configuration commands, one per line. End with CNTL/Z.
router(config)#fabric link heuristic shutdown
router(config)#end
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Copyright © 2005
Avici Systems Inc.
Avici® and TSR®
is a registered trademark of Avici Systems Inc.
IPriori™, Composite Links™, SSR™, QSR, and NSR® are
trademarks of Avici Systems Inc.
Source
File Name: FABRICconfig.fm
HTML File Name: FABRICconfig.html
Last Updated: 02/25/05 at 15:19:44