QoS DSCP Replacement

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Hi there,

I I ́m new to QoS and I just got ask to apply it to all of the voice vlan. What I did was, a QP (QP6) and configure the diffsev examination for code-point 46 and then I enabled the diffserv examination on all the ports and disabled the dot1p examination on all the ports. When I use the show port <port> qosmonitor command, I do see traffic in the QP6.

In one of the ports I see traffic from QP1 & QP6 but from that port in specific I want all ingress and eggress traffic to be QP6, How can I do  that? Can the switch change the DSCP?
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Erick Cruz

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Posted 4 years ago

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Sumit Tokle, Alum

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For ingress you need to create a meter and then assign that meter to the port or traffic using an ACL.  The meter will drop any traffic that is over the meter.  For egress you need to define a qosprofile using the command create qosp qp5 for example then assign that traffic to the qosprofile and finally put a maximum setting on the traffic using the command config qosp qp5 peak_rate 2 M ports <port_list>
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Erick Cruz

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Thank you Sumit Tokle for your help, But I think I did not make my self clear, I have both QP 1 and 6 having traffic, QP6 with packets with a DSCP of 46 and QP1 with any other DSCP. What I want is to make all of the packets with any other DSCP go out of a specific port (example port 24) with a DSCP of 46 so that when that packet goes to another switch, the switch can see that it has a DSCP of 46 and send it to QP6.

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Sumit Tokle, Alum

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I believe above requirement can easily be configured using Policy based QoS.

Create the policy file, in matching condition you could mention the DSCP value that switch has to see and assigned it to certain QoS profile name also you could redirect this matching traffic to specific port.
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Erick Cruz

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Ok and how can i change the DSCP value, lets say that I get a packet with a DSCP value of 40 how can the switch change it to a value of 46?

Thanks Alot
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Sumit Tokle, Alum

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To replace DSCPs by enabling DiffServ replacement, use the command:"enable diffserv replacement ports [port_list| all]"  The port in this command is the ingress port.

To view the current DiffServ replacement configuration, use the command:"show diffserv replacement"

To change the DSCP mapping, use the commands:
"configure diffserv replacement [{qosprofile} qosprofile| priority priority]
code-point code_point"


DiffServ Example

In this example, we use DiffServ to signal a class of service throughput and assign any traffic coming from network 10.1.2.x with a specific DSCP. This allows all other network switches to send and observe the DSCP instead of repeating the same QoS configuration on every network switch.
To configure the switch:
1 Using ACLs, assign a traffic grouping for traffic from network 10.1.2.x to QP3:

configure access-list qp3sub any

The following is a sample policy file example:

#filename: qp3sub.pol

entry QP3-subnet {
if {
source-address 10.1.2.0/24
} then {
Qosprofile qp3;
replace-dscp;
}

2 Configure the switch so that other switches can signal calls of service that this switch should
observe.
enable diffserv examination ports all

If you are using ACL-based traffic groups, you can use the replace-dscp action modifier to replace theingress DSCP value with the DSCP value of the egress QoS profile
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Erick Cruz

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Thaks alot I will try to work with this and I will let you know the outcome.
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Boon Nyian Jap

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Hi, if we are using vlan based traffic group, can we change the ingress DSCP value so that it will be prioritized at ingress? Or the vlan traffic group configuration below will be replaced at egress only?

enable diffserv replacement ports all
disable dot1p examination ports all
enable diffserv examination ports all
configure vlan vlan_name {qosprofile} qosprofile
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Jarek

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Hi,


the concept guide says that - "VLAN-based traffic groups forward traffic to egress QoS profiles based on the VLAN membership of the ingress port.", then the "configure vlan vlan_name {qosprofile} qosprofile" will only put the traffic at egress only.

So, if you want change the DSCP for specific vlan to value associated with qos profile qp6:

entry VoIP { if match all {
    vlan-id 201 ;
} then {
   Qosprofile qp6;
    replace-dscp;

} }


--
Jarek