Implementing QOS for over multiple Switches for two Vlans

[admincrosbypremier]

afternoon all i was looking for a bit of help in configuring QOS for two VLANS i have created. these will be for voice traffic vlan 22 and video traffic vlan23. i also have three other vlans for pc's, wireless devices and our cnc machines. we have 5 switches that are all SG30028P's with a single switch doing the intervlan routing (operating at layer 3). all of the switches are trunked back to the main switch and ive been through the guide written on how to do this on a single switch which i dont think is layer 3.

could anyone help me with this as i want the video and voice to take priority over the rest of the traffic

regards Patrick

[Tom Watts]

Hello Patrick,

For the voice traffic, the auto voice vlan should take care of that for you. If you're only using telephones and need only that traffic priority, there are a myriad of features for this such as LLDP-MED, telephony oui and even basic QoS.

It is genuinely dependent on your topology and how things are plugged in (computer behind telephone? multicast video somewhere..? etc)

You can reference this community post for some ideas on advance QoS.

https://supportforums.cisco.com/message/3683428#3683428

[admincrosbypremier]

thanks thomas the video streaming would be from security camera's so i dont think i will be able to get arround this using the single telephone Oui. My question is will basic QOS on these switches manage this by them self or does it still need tuning?

[Tom Watts]

Here is the documentation per;

http://www.cisco.com/en/US/docs/switches/lan/csbms/sf30x_sg30x/administration_guide/78-19308-01.pdf

Basically, what this is saying, if you configured basic QoS, all traffic that is classified as the same will be treated the same. It means phone A cannot have priority over phone B (this is true for your video as well). This is determined by the egress queue on the egress port. Additionally, if you have QoS assigned upstream, the port will trust whatever tag is there.

The QoS mode that is selected applies to all interfaces in the system.

• Basic Mode—Class of Service (CoS).

All traffic of the same class receives the same treatment, which is the single

QoS action of determining the egress queue on the egress port, based on

the indicated QoS value in the incoming frame. This can be the VLAN

Priority Tag (VPT) 802.1p value in Layer 2 and the Differentiated Service

Code Point (DSCP) value for IPv4 or Traffic Class (TC) value for IPv6 in Layer

3. When operating in Basic Mode, the switch trusts this external assigned

QoS value. The external assigned QoS value of a packet determines its

traffic class and QoS. The header field to be trusted is entered in the Global Settings page. For

every value of that field, an egress queue is assigned where the frame is

sent in the CoS/802.1p to Queue page or the DSCP to Queue page

(depending on whether the trust mode is CoS/802.1p or DSCP,

respectively).

[admincrosbypremier]

okay thanks for the reply so if i wanted the ip camera's to take priority over someone streaming a movie then i would need advanced QOS. do i need to do anything different on the layer 3 switch to the other switches?

[Tom Watts · Accepted solution]

Right, this way you can give the IP or MAC address priorities.

No, there is nothing different, only consideration of routing. Since the L3 switch can make local routing decisions, the ACL placement can change. In a L2 environment, all packets are forwarding to the router then back down the network to the local destination, so you can dump an ACL on the uplink.

Since you have a L3 switch, you can practice the same, dump an ACL on the downstream link to the L2 switches to have all traffic subject to the ACL. Anything connecting to the L3 switch, you can of course apply an ACL to the router uplink to get all inbound traffic remark correctly. You can also apply a policy on the source port interface to get the remark as soon as traffic hits the switch.

QoS policy is the same concept of an ACL, you want it closest possible to the resource. If you apply a QoS policy up an uplink, the QoS will be marked when it hits that port. Not before. Therefore it should be applied closest to the device as possible. Many times, local QoS is not as important until it starts to get to the router. As most Cat 6 environments can generally handle any local traffic. So, depending on the # of devices and the amount of traffic, a decently robust network can handle all local traffic then you just prioritize the uplink remarks to ensure what is important is first.