QoS and VLAN

[dgrizzard]

Couple of questions regarding QoS and VLAN:

I have a 2626 and a 2824 switch for reference...

1) Do I need to do anything special to trust dscp or do passthrough for dscp tagging to my router?
2) I have qos dscp-map priority setup right now for my voip traffic/signaling, traffic is setup at 7, this is correct to give it the highest priority of traffic right?
3) In the advanced traffic guide it says something to the effect of the port must be tagged on a VLAN to pass the DSCP tag, does the port really need to be tagged, or is leaving it untagged on the default VLAN fine?
4) If I setup a separate VLAN for my VoIP phones (assume the PCs will be plugged into the phones) do I need to tag both the PC VLAN and the phone VLAN? Or should I only tag the phone VLAN (since it is an 802.1p/q device) and not the PC?

If there is any other help that someone can give to make sure I have these switches setup properly that would be great.

TIA

 

[TheBublitz]

1) Do I need to do anything special to trust dscp or do passthrough for dscp tagging to my router?

What kind of router you using? As long as the packets are tagged with with a DSCP value via switch/phone system you should be able to set priority or bandwidth over wan links. As long as your router supports DSCP Qos.

2) I have qos dscp-map priority setup right now for my voip traffic/signaling, traffic is setup at 7, this is correct to give it the highest priority of traffic right?

How are you assigning DSCP? IP source/destination, Port numbers TCP UDP, vlan id or this value already set in the phone system? Using 7 is fine usually I set mine to 6 in case my network changes and some other network traffic becomes more important to the company.

3) In the advanced traffic guide it says something to the effect of the port must be tagged on a VLAN to pass the DSCP tag, does the port really need to be tagged, or is leaving it untagged on the default VLAN fine?

This is true if the 802.1q tag isn't present the priority is dropped.

BUT just because a port is set to untagged doesn't mean it gets to destination untagged.

If the traffic is forwarded to another switch the trunk port(port connecting 2 switches together) will add the vlan tag (and the priority). The only way the vlan tag will be stripped if the destination port is set to untagged. So the vlan and priority will be stripped before sent to the device on the destination port. So there will be some QoS unless the packet goes to a device on the same switch and that port is set to untagged on that vlan.

This ONLY applies if you are assigning a DSCP value/priority via vlan ID. If you are assigning DSCP value in your phone switch you can setup a policy in your switches based on that value, Or just tagg all your VOIP ports like the HP doc states.

4) If I setup a separate VLAN for my VoIP phones (assume the PCs will be plugged into the phones) do I need to tag both the PC VLAN and the phone VLAN? Or should I only tag the phone VLAN (since it is an 802.1p/q device) and not the PC?

Only tagg the Phone vlan. Most PC nics will not support 802.1q packets.

Billy Bublitz
Integrity Windows and Doors

 

[dgrizzard]

Bublitz,
Thanks for the response..

1) My phones do tag with a 46 value for voice traffic and 40 for signaling, I believe the procurve switches have a priority of 7 for 46 by default. I also have a Cisco 1841 with qos setup on this as well to prioritize dscp traffic across the wan.

3) At this site there is actually only 1 switch and 1 router so there is no trunking involved. In this setup I wouldn't have to worry about the switch stripping the dscp tag correct?

Thanks again!

 

[TheBublitz]

3) If the 1841 router doesn't have sub interfaces with encapsualtion dot 1q configured, with the same dscp policy configured as the switches, then once the traffic hits the router you would have to strip the tag.

Since your traffic is already tagged by the phone switch. You do not need to use vlan id dscp tagging.

ftp://ftp.hp.com/pub/networking/software/AdvTraff-Oct2005-59908853-Chap06-Qos.pdf

Page 6-41 would be the way to go. Assigning an 802.1p Priority to IPv4 Packets on the basis of Incoming DSCP. You would also use this simular model on your router. I would still suggest using vlans to seperate your lan from voice and data. This way you can configure all your phones to vlan 2 untagged and still have QoS.

Billy Bublitz
Integrity Windows and Doors