04-10-2020 02:55 AM
Hi All,
I was hoping someone could assist me in explaining what the function is of the below commands on a cisco switch interface?
srr-queue bandwidth share 1 30 35 5
priority-queue out
mls qos trust cos
auto qos trust
Many Thanks!
Kind Regards,
Ryan
Solved! Go to Solution.
04-10-2020 03:23 AM
Hello Ryan,
the QoS effective implementation on switches is platform dependent.
The commands that you have provided are likely on a Catalyst 3560.
In short this kind of switches have an hardware oriented QoS very different from the modular QoS of SW based routers.
When an ethernet frame carrying an IP packet in the payload is received on the input interface a switch like this performs a classification and associates a DSCP value ( it is in the IP header) to the frame.
On the outgoing inteface there is a limited number of hardware based queues , the switch uses a DSCP to COS mapping matrix to find the outgoing queue for the packet/frame.
More specifically the commands that you have listed do the following:
>> priority-queue out
It enables the priority queue that you can see like a low latency queue and it should be used for VOIP packets
>> mls qos trust cos
This command instructs the switch in how to dea with received frames. The CoS is a subfield of 802.1Q header so this command should appear only on a L2 trunk port or port-channel.
The possible values of CoS 0 to 7 are mapped to the 4 outgoing queues.
>> auto qos trust
Auto-QoS is a set of macro that allow to deploy QoS on swictches without manually entering each single command.
>>
srr-queue bandwidth share 1 30 35 5
There are four queues, one is set as priority and served first when the PQ is empty the interface will take frames / bytes from the three standard queues according to the relative weights specified in the command.
Each standard queue can be actually of two types : shared round robin allowed to take more then its weight if the interface is empty or it can be policed so it cannot go beyond its weight (this is called Shaped round robin).
To be noted in more modern switches like C3650, C3850 and newer C9x00 the QoS is modular like in SW based routers and you can use policy-maps.
Hope to help
Giuseppe
04-10-2020 03:14 AM
Have a look at this document, start with reading it, then you will also find the mentioned commands explained
M.
04-10-2020 04:03 AM
Thanks Marc!
I will have a read over these documents!
Kind Regards,
Ryan
04-10-2020 03:23 AM
Hello Ryan,
the QoS effective implementation on switches is platform dependent.
The commands that you have provided are likely on a Catalyst 3560.
In short this kind of switches have an hardware oriented QoS very different from the modular QoS of SW based routers.
When an ethernet frame carrying an IP packet in the payload is received on the input interface a switch like this performs a classification and associates a DSCP value ( it is in the IP header) to the frame.
On the outgoing inteface there is a limited number of hardware based queues , the switch uses a DSCP to COS mapping matrix to find the outgoing queue for the packet/frame.
More specifically the commands that you have listed do the following:
>> priority-queue out
It enables the priority queue that you can see like a low latency queue and it should be used for VOIP packets
>> mls qos trust cos
This command instructs the switch in how to dea with received frames. The CoS is a subfield of 802.1Q header so this command should appear only on a L2 trunk port or port-channel.
The possible values of CoS 0 to 7 are mapped to the 4 outgoing queues.
>> auto qos trust
Auto-QoS is a set of macro that allow to deploy QoS on swictches without manually entering each single command.
>>
srr-queue bandwidth share 1 30 35 5
There are four queues, one is set as priority and served first when the PQ is empty the interface will take frames / bytes from the three standard queues according to the relative weights specified in the command.
Each standard queue can be actually of two types : shared round robin allowed to take more then its weight if the interface is empty or it can be policed so it cannot go beyond its weight (this is called Shaped round robin).
To be noted in more modern switches like C3650, C3850 and newer C9x00 the QoS is modular like in SW based routers and you can use policy-maps.
Hope to help
Giuseppe
04-10-2020 04:00 AM
Thanks for you explanation Giuseppe I appreciate it!
Kind Regards,
Ryan
04-10-2020 10:04 AM
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