Cisco Systems ASA5515K9, ASA 5500 Configuring the Standard Priority Queue for an Interface

54-7
Cisco ASA 5500 Series Configuration Guide using the CLI
Chapter54 Configuring QoS
Configuring QoS
Table54-2 shows how to calculate the TX ring limit. This limit determines the maximum number of
packets allowed into the Ethernet transmit driver before the driver pushes back to the queues on the
interface to let them buffer packets until the congestion clears. This setting guarantees that the
hardware-based transmit ring imposes a limited amount of extra latency for a high-priority packet.
Configuring the Standard Priority Queue for an Interface
If you enable standard priority queuing for traffic on a physical interface, then you need to also create
the priority queue on each interface. Each physical interface uses two queues: one for priority traffic,
and the other for all other traffic. For the other traffic, you can optionally configure policing.
Note The standard priority queue is not required for hierarchical priority queuing with traffic shaping; see the
“Information About Priority Queuing” section on page54-3 for more information.
Restrictions
•(ASASM) The ASASM does not support priority queuing.
•(ASA 5580) You cannot create a standard priority queue for a Ten Gigabit Ethernet interface. Note:
For the ASA 5585-X, standard priority queuing is supported on a Ten Gigabit Ethernet interface.
•(ASA 5512-X through ASA 5555-X) Priority queuing is not supported on the Management 0/0
interface.
1. For example, DSL might have an uplink speed of 768 Kbps. Check with your provider.
2. Determine this value from a codec or sampling size. For example, for VoIP over VPN, you might use 160 bytes. We recommend 256
bytes if you do not know what size to use.
3. The delay depends on your application. For example, the recommended maximum delay for VoIP is 200 ms. We recommend 500 ms
if you do not know what delay to use.
Table54-2 TX Ring Limit Worksheet
Step1
__________
Outbound
bandwidth
(Mbps or Kbps)1
1. For example, DSL might have an uplink speed of 768 Kbps.Check with your provider.
Mbps x125 =__________
# of bytes/ms
Kbps x0.125 =__________
# of bytes/ms
Step2
___________
# of bytes/ms
from Step1
÷
__________
Maximum packet
size (bytes)2
2. Typically, the maximum size is 1538 bytes, or 1542 bytes for tagged Ethernet. If you allow jumbo frames (if supported for your
platform), then the packet size might be larger.
x__________
Delay (ms)3
3. The delay depends on your application. For example, to control jitter for VoIP, you should use 20 ms.
=__________
TX ring limit
(# of packets)