Cisco 10000 - Manual (Page 67)

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Cisco 10000 Series Router Software Configuration Guide
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Chapter 2 Scalability and Performance
Scaling Enhancements in Cisco IOS Release 12.3(7)XI2
On low-speed interfaces, the default queue size is 8 for all QoS CBWFQ queues, with the exception of
WRED queues. The default queue size for WRED queues is 32.
The class-default queue size on low-speed interfaces has changed from 32 to 8. If the traffic is too bursty
and packets drop, you can use the queue-limit command to increase the class-default queue size.
If you change the queue size for 131,072 queues while traffic is running, the queue size for a few queues
might not be changed if packets were in the queues. An “out of resource” message can also appear. Use
the queue-limit command to modify the queue size for those queues that were not changed.
The queue limits packet buffers can become fragmented after the queue sizes on 131,072 queues has
been changed a few times. The system might indicate that there are not enough resources to increase
queue size, even though there are enough free packet buffers. Removing and reapplying the policy map
on the interfaces solves this problem.
Use the show pxf cpu queue summary command to see the number of packet buffers, packet buffers
being recycled, and free packet buffers.
Scaling Enhancements in Cisco IOS Release 12.3(7)XI2
Cisco IOS Release 12.3(7)XI2 provides increased limits with queue scaling and VC scaling.
Queue Scaling
At least two queues are allocated for every interface or subinterface for which separate queues are
created. The first queue is the default queue for normal traffic, and the second queue, known as the
system queue, is used for a small amount of router-generated traffic that bypasses the normal drop
mechanisms. For 32,000 VCs, this setup would require the allocation of a minimum of 64,000 queues.
While Cisco IOS Release 12.3(7)XI1 adds support for up to 128,000 queues, a more effective use of
these limited resources is realized by having the subinterfaces on a given main interface share the single
system queue of the main interface.
In Cisco IOS Release 12.3(7)XI2, the subinterfaces on a given main interface share the single system
queue of the main interface, which allows for 32,000 subinterfaces with a three-queue model that
supports assured forwarding (AF) queues and expedited forwarding (EF) queues, in addition to the
default best effort (BE) queues. Because a system queue does not exist for every subinterface, this setup
frees up queues for a 4-queue model.
VC Scaling
When configured for hierarchical shaping, ATM line cards support the following number of VCs:
• E3/DS3 line card supports a maximum of 4,096 VCs
• OC-12 ATM line card supports a maximum of 16,384 VCs (previously 14,436)
• OC-3 ATM line card supports a maximum of 8,191 VCs