it should be noted that the fair-queue command does not show up in the router configuration
unless it has been modified from the default of 64, or disabled using the no fair-queue
command.
Priority queuing gives the network administrator granular control that reduces network delay
for high-priority traffic. Variations of priority queuing have been in use for a number of years
in differing vendor implementations.
low. For traffic placed in individual queues, the output strategy is FIFO. The traffic defined as
high priority receives the benefit of all available resources on the output interface until the
queue is empty. Once the high queue is complete, the medium queue traffic is dispatched in the
same manner until empty.
If there are no entries in the high queue after servicing the medium queue, the normal queue is
emptied. Once normal traffic has been dispatched, the high queue is checked again, followed
by the medium and normal queues. If all three are empty, the low queue is serviced. The result
is that high-priority traffic always suffers the shortest delay in awaiting dispatch. Figure 10-5
illustrates the concept of priority queuing.
serviced. The traffic can even age out and be purged from memory if the queue overflows. Once
an overflow occurs, all new packets for that queue are dropped until space is freed up in the
queue. Each queue has a fixed length, which is configurable. The defaults are as follows:
is due to the queuing algorithm and the fact that the lower priority queues might wait longer to
be serviced. During the wait, a traffic jam of sorts can build up. To keep the queue from
overflowing and dropping traffic, a larger queue size is necessary.
in this industry, if it works, don't mess with it.