Auto QoS

[aoshea]

Dear Netprof,

Just trying to implement QoS for two avaya telephone switches on two separate sites connected via a laser link (200Mbps (2 x 100Mbps laser links trunked)).

The avaya switches use a DSCP of 46, if I use the auto QoS, but just use the 'trust' statement on (each fast eth int at each site) rather than the 'trust cisco-phone' will the traffic still be placed in the expedite queue (queue 4 on the 2 x 3550 EMI that are located at each site)?.

Thanks in advance.

Regards, Adrian.

[pflunkert]

Hello Adrian,

Trust the CoS value in the incoming frame (configure the port to trust CoS). Then, the switch uses the configurable CoS-to-DSCP map to generate the internal DSCP value. Layer 2 ISL frame headers carry the CoS value in the three least-significant bits of the 1-byte User field. Layer 2 802.1Q frame headers carry the CoS value in the three most-significant bits of the Tag Control Information field. CoS values range from 0 for low priority to 7 for high priority.

The trust DSCP and trust IP precedence configurations are meaningless for non-IP traffic. If you configure a port with either of these options and non-IP traffic is received, the switch assigns the default port CoS value and generates the internal DSCP from the CoS-to-DSCP map.

When your mapping shows DSCP 46 to the expedite queue it will sent to.

All will works as you expected.

Regards

Peter

[aoshea]

Many thanks for the information, if the telephone switch is already marking voice traffic with dscp 46, do I need to worry about CoS (you mention to trust CoS) or do I still need to create an ACL to mark inbound traffic ?

I have attached a bmp file that shows a screen shot from the one of the avaya switches (same settings on each site).

Thanks again for your assistance.

Regards,

Adrian

[pflunkert]

Hello Adrian,

when you trust the DSCP values, you do not need to create an ACL. When you will sniffer the outgoing traffic, you can see that the DSCP values still exists.

Regards

Peter

[aoshea]

Many thanks for the response, so hopefully as long as I issue the 'auto qos voip trust' on both the 10/100 fe ports that the avaya telephone switches connected to at each site and also on the trunk ports that connects the sites. Then (hopefully) i should have QoS between the two avaya telephone switches?

thanks again in advance.

Regards Adrian.

[kirkster]

Thats correct. Just trust the cos incomimng and it will work. If you want you can also do a "mls qos cos 5" on the port together with the mls qos trust cos command. This will write a cos of 5 inot he packets from the telephone switches. Then all atraffic on uplinks between switches will put cos of 5 by default into the priority queue.

Hope that helps.

Steve