Each queue has a limit on the number of packets that the router can place into the queue. This limit, referred to as the depth,
is a user-configurable limit. During periods of high traffic, a queue fills with packets that are waiting for transmission.
When a queue reaches its queue limit and becomes full, by default, the router drops packets until the queue is no longer full.
For the Cisco ASR 1000 Series Router in Cisco IOS XE Software Release 2.1, the packets-per-queue range is 1 to 2,000,000.
When a packet queue temporarily experiences congestion, increasing the depth of the queue using the queue-limit command reduces
the number of packets dropped. However, setting the queue limit to a high value might reduce the number of packet buffers
available to other interfaces.
If you do not specify a queue limit, the router calculates the default buffer size for each class queue as follows:
Class queues --The router uses 50 ms of 1500-byte packets but never less than 64 packets.
Class queues on ESP40--The router uses 25 ms of 1500-byte packets but never less than 64 packets.
Priority queues --The router uses a queue limit of 512 packets.
When setting the queue limit, decide how many users will be active at any given time and tune the queue limits accordingly.
This will allow individual interfaces to handle traffic bursts and not deplete the available memory. For assistance, contact
the Cisco Support website at