Queuing on Interfaces Versus Subinterfaces and Virtual Circuits
IOS queuing tools can create and manage software queues associated with a physical interface,
and then the packets drain into the hardware queue associated with the interface. Additionally,
queuing tools can be used in conjunction with traffic shaping. Traffic-shaping tools delay packets
to ensure that a class of packets does not exceed a defined traffic rate. While delaying the packets,
the shaping function queues the packets—by default in a FIFO queue. Depending on the type of
shaping tool in use, various queuing tools can be configured to manage the packets delayed by the
shaping tool.
Chapter 14, “Shaping and Policing,” covers traffic shaping, including how to use queuing tools
with shapers. The queuing coverage in this chapter focuses on the implementation of software
queuing tools directly on the physical interface.
Comparing Queuing Tools
Cisco IOS provides a wide variety of queuing tools. The upcoming sections of this chapter
describe several different IOS queuing tools, with a brief summary ending the section on queuing.
Table 13-2 summarizes the main characteristics of different queuing tools that you will want to
keep in mind while comparing each successive queuing tool.
Key Comparison Points for Queuing Tools
Feature Definition
Classification The ability to look at packet headers to choose the right queue for
each packet
Drop policy The rules used to choose which packets to drop as queues begin
to fill
Feature Definition
Scheduling The logic used to determine which packet should be dequeued next
Maximum number of queues The number of unique classes of packets for a queuing tool
Maximum queue length The maximum number of packets in a single queue