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This chapter describes how to increase scaling of neighbors in a hub and spoke deployment using the following configuration options:
Reducing flooding over parallel peer-to-peer links
Staggered synchronization of adjacencies after router reload
Configuring and monitoring IS-IS queue
It is assumed that you already have IS-IS running on your network.
Before performing the tasks in this module, you should be familiar with the concepts described in the "Overview of IS-IS Fast Convergence" module.
In the presence of parallel links to the same neighbor, redundant flooding of link state packet (LSP) updates occur on each link, by default. This when combined with large number of neighbors, exponentially increases the CPU processing time required to synchronize the LSP database. The suppression of flooding over parallel links improves performance at scale with no loss of reliability.
The simultaneous boot up of a large number of adjacencies after a reboot or IS-IS process restart can result in overflow of input queues due to receipt of redundant link state information from multiple neighbors. To avoid such situations, it is important to stagger synhronization of adjacencies and also limit the maximum number of adjacencies that are in syncing state. This mechanism also helps in situations where network issues may affect synchronization of adjacency information on some interfaces.
 Note |
Staggered synchronization of adjacencies is only supported on point-to-point interfaces |
For large scale deployments, when the queue reaches a high watermark, it can lead to dropping of packets. In such a situation, it is important to adjust the IS-IS queue size to handle high loads. Additionally, you can monitor the IOS queue to check:
Current state of the IS-IS input queue
Queue size maximum limit
Highest water mark (maximum size queue reached since last set of counters were cleared)
Number of drops
enable
configure terminal
router isis [area-tag]
flood parallel suppression
By default, flood suppression functionality is enabled.
enable
clns queue-depth <size>
enable
configure terminal
router isis [area-tag]
adjacency stagger <initial> <max>
This feature is disabled by default. If staggering of adjacencies is enabled, you can use the show isis protocol command to see the active values as well as the syncing and full count of point-to-point adjacencies.
You can use the show clns traffic command to check:
Actual queue size
Queue size maximum limit
Highest water mark (maximum size queue reached since last set of counters were cleared)
Number of drops
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