Queue 0 is reserved by IOS for keepalives, signaling, and other system-critical functions. It is emptied before any of the queues 1 through 16 are processed.
As with priority queues, custom queues can be applied to a particular interface or protocol. Packets that do not match any of the allocations specified in the access list will be placed into queue number 1, although this behavior can be changed using the queue-list <list-number> default <queue-number> command. Within any particular custom queue, the algorithm is FIFO.
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