54-6
Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter54 Configuring QoS
Configuring QoS
(ASA 5512-X through ASA 5555-X) Priority queuing is not supported on the Management 0/0
interface.
Additional Guidelines and Limitations
For traffic shaping, you can only use the class-default class map, which is automatically created by
the ASA, and which matches all traffic.
For priority traffic, you cannot use the class-default class map.
For hierarchical priority queuing, for encrypted VPN traffic, you can only match traffic based on the
DSCP or precedence setting; you cannot match a tunnel group.
For hierarchical priority queuing, IPsec-over-TCP traffic is not supported.
You cannot configure traffic shaping and standard priority queuing for the same interface; only
hierarchical priority queuing is allowed.
For standard priority queuing, the queue must be configured for a physical interface or, for the ASA
5505, a VLAN.
Configuring QoS
This section includes the following topics:
Determining the Queue and TX Ring Limits for a Standard Priority Queue, page54-6
Configuring the Standard Priority Queue for an Interface, page54-7
Configuring a Service Rule for Standard Priority Queuing and Policing, page54-9
Configuring a Service Rule for Traffic Shaping and Hierarchical Priority Queuing, page54-12

Determining the Queue and TX Ring Limits for a Standard Priority Queue

To determine the priority queue and TX ring limits, use the worksheets below.
Table54-1 shows how to calculate the priority queue size. Because queues are not of infinite size, they
can fill and overflow. When a queue is full, any additional packets cannot get into the queue and are
dropped (called tail drop). To avoid having the queue fill up, you can adjust the queue buffer size
according to the “Configuring the Standard Priority Queue for an Interface” section on page 54-7.
Table54-1 Queue Limit Worksheet
Step1
__________
Outbound
bandwidth
(Mbps or Kbps)1
Mbps x125 =__________
# of bytes/ms
Kbps x.125 =__________
# of bytes/ms
Step2
___________
# of bytes/ms
from Step1
÷
__________
Average packet
size (bytes)2
x__________
Delay (ms)3
=__________
Queue limit
(# of packets)