QoS configuration within LAN

[soonli.lim]

I need some advice regarding QoS configuration for a 2 tier LAN. The top tier will comprise of the typical pair of core switches and these are trunked to the 2nd tier of user access switches. Let's say one of these user access switches uses VLAN 100 for data and VLAN 200 for IPT and each user access port is configured with "mls qos vlan-based". The following basic commands have been input on all core and user access switches.

class-map EF

match access-group name IPT

policy-map LAN

class EF

set dscp ef

access-list IPT has been created to include all host using the relevant IPT ports.

The command "service-policy input LAN" has been applied to SVIs for VLANs 100 and 200 on the 2 core switches. My question is, do we need to explicitly create SVIs for VLANs 100 and 200 on the relevant layer-2 user access switch and apply the command "service-policy input LAN" to these SVIs since the user access ports are using "mls qos vlan-based"? My thought is that if this is not done, the command "mls qos vlan-based" will not be useful.

[Vaibhava Varma]

Hi Lim

Service-Policy will be applied at the L3 Gateway of the VLANs in question which is at the Core-Switches in this case.

On the access-switches we don't need the SVI for the VLANs as they are doing just L2 Transport. However we would need an SVI for the MGMT purpose on the access switches. Access Switches just do L2 switching for the user frame and do not look at the L3 Packet information which is encapuslated inside Layer 2 Payload.

Hope this helps to answer your query.

Regards

Varma

[soonli.lim]

Thanks Varma.

The network info portion in our Avaya phones shows the following.

L2 Audio 5

L2 Signaling 3

L3 Audio 46

L3 Signaling 46

If I understand correctly, the phone will encapsulate the DSCP 46 information within the layer-2 frame which has COS value 5 and these frames get to the layer-2 user access switch. Because of "mls qos vlan-based", the stripped down frames which become IP packets within the core switches will then conform to the policy-map which has been applied to the relevant data/IPT VLANs. Please advise.

[Vaibhava Varma]

Hi Lim

Yes this is the way the traffic flow will be -L2 on the acces switches and L3 from the core switches.

Regards

Varma

[soonli.lim]

Am I correct to say that if we use port-based configuration instead (apply "service-policy input LAN" directly to user access ports), it is not necessary to apply the same policy to the SVIs on the core/distribution layers?