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Questions about transmit queues and other QoS features of 4500 chassis

What kind of transmit queues does a WS-x4712-SFP+E have available?

I am looking at the spec sheet but cannot determine -

I believe this would be either 1P7Q1T or 1P7Q?

Also, according to some documentation I read the 4500 chassis don't support ingress queueing or WRED, is this correct?

Everyone's tags (1)
Cisco Employee

Hi Dear,Please find the

Hi Dear,
Please find the answer below:-

The above specified module Inherits Supervisor Engine QoS capability.


2- Second question:  Simple answer is "YES" it doesnt support WRED but there is different method. 

Please find the QOS on 4500:

Quality of Service (QoS) processing on the 4500 series switch is done at the supervisor module. QoS support requires the Supervisor 2+ or later supervisor module with each supervisor supporting different capabilities. QoS processing is not turned on by default. QoS is turned on by using the following global IOS command: Cat4500(config)#qos There are many configuration commands on the 4500 that are similar to commands used on other native IOS switches, but command syntax never includes the mls prefix (multi-layer switching). The 3550/3560/2960/2970/3750 switches require the mls qos command to globally enable qos processing. The Catalyst 4500 supports a unique congestion avoidance algorithm called DBL (dynamic buffer limiting). The 2950/3550/6500 switches support the WRED congestion avoidance algorithm that works on a per packet basis, while DBL works at the flow level. A flow is identified by the VLAN combined with the source and destination layer 3 (IP Address) and layer 4 (TCP/UDP port) information. DBL allows behaving flows to be preserved while misbehaving aggressive flows are punished as a queue exceeds a configurable threshold. DBL is effective with non-adaptive flows (NAF), while WRED is not. Non-adaptive flows do not respond to packet loss by lowering their window sizes like TCP based traffic. Most UDP based applications (voice and/or video) are like packet generators because they do not throttle back their rates in any way when packets are lost. DBL must be configured globally with the following command syntax: Cat4500(config)#qos dbl The DBL capabilities of the switch also have the ability to mark the explicit congestion notification (ECN) bits of the type of service (ToS) byte in the IP header. RFC3168 introduced ECN capabilities into the type of service byte so routers and switches could mark packets as congestion experienced when queues exceed a threshold. The source or destination TCP/IP stack will then lower their window size to react to the congestion on the network. Congestion avoidance algorithm are utilized during periods of congestion, which begs the question: Why are the mechanisms called congestion avoidance if they kick in during periods of congestion? The algorithms avoid full queue congestion which would result in tail drop where all traffic is dropped regardless of priority. The ECN capabilities are enabled with the following command: Cat4500(config)#qos dbl exceed-action ecn The global DBL commands shown above enable the use of the dbl command in individual classes at the policymap-class configuration level. The 4500 switch supports CoS and DSCP trust boundary configurations, but all QoS internal processing and transmit queue mapping is done based on the DSCP. Classification and marking is supported with the use of a service-policy, but only certain line card modules can have a service-policy directly attached to a port. Classification and marking policies are applied to vlans on the 4500 by default, but newer versions of IOS on the 4500 allow per vlan, per port QoS. An example of per port, per vlan QoS is shown below: Cat4500(config)#interface gigabitethernet 5/1 Cat4500(config-if)#vlan-range 5-10 Cat4500(config-if-vlan-range)#service-policy input classify-mark In the above example, the policy-map named classify-mark is applied to input traffic on vlan 5 through 10 on gigabitethernet 5/1 which is an 802.1q trunk to another switch. Other VLANs on the interface do not have this policy-map attached to their traffic. The 4500 queue architecture includes 4 queues in which DSCP values are mapped to the individual queues. Newer line card modules like the Supervisor Engine 6-E have eight transmit queues in which traffic can be mapped. We will take a look at the DSCP mapping used in the four queue architectures. The queue mapping is as follows: DSCP Range Queue number 0-15 1 16-31 2 32-48 3 49-63 4 Queue 3 can be configured as a priority queue and shaped to 1Mbps with the following command syntax: Cat4500(config)#interface gigabitethernet 5/1 Cat4500(config-if)#tx-queue 3 Cat4500(config-if-tx-queue)#priority high Cat4500(config-if-tx-queue)#shape percent 33 Cat4500(config-if-tx-queue)#bandwidth percent 33 The priority queue shaping option is similar to shaped round robin (SRR) on the 2960/2970/3560/3750 switches. Each queue can be assigned a bandwidth parameter to control the weighting of each queue’s processing during periods of congestion. Only the bandwidth percentage of queue 3 is shown in the example above. Ingress and egress policers are supported on the 4500 switch. The police command on the 4500 switch supports speed increment keywords (kbps and mbps) to indicate the rates at which traffic should be policed. Other switches require rates to be configured in bits per second (bps) which results in long, cumbersome numbers. The 4500 QoS commands and capabilities differ by supervisor module. For more information on the 4500 QoS capabilities, check out the reference links below. REFERENCES Quality of Service on Cisco Catalyst 4500 Series Quality of Service on the Cisco Catalyst 4500 Supervisor Engine 6-E Configuring Quality of Service – 12.2(52)SG 
QoS SRND - Catalyst 4500 Supervisor II+/III/IV/V—QoS Considerations and Design





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Thanks for the response.I was

Thanks for the response.

I was under the impression the queues and such come form the hardware... Or maybe that is other platforms (6500's)?

The supervisor is a Sup 7-E. i see on the spec sheet that it has 8 queues; is it safe to assume one of them is priority?

I'm struggling with determining thresholds. I see queuing policies like 1p3q4t, 1p7q4t, 8q2t but haven't found a good command (or way) to determine these threshold values?

Cisco Employee

Hi Dear,I didn't had a time

Hi Dear,

I didn't had a time to play with the QOS on this box hence cant say you the practical way how this reacts/works.

Coming down to 6500 yes you are correct.

Second coming to the threshold I found the below link:

Check if those above links answers your query else I can do some more research and update you.





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Cisco Employee

Okay.,Some more to add


Some more to add:

4500 series switches has MQC QOS and 6500 has MLS QOS.  So, they both differs slightly in
CLI and features.

QOS support on the 6500 and 6500 line cards is far superior to the 4500. The newer blades
on the 6500 are fabric-enabled, and have a 40-Gbit connection to the backplane, which
connects the blade to a Supervisor module. Internally within those blades that have DFCs
(Distributed Forwarding Card), the throughput on the card itself (say going from one port
on the card to another) is 64-Gbit.

Below is the document we suggest to follow:

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