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Cisco QOS

Tim Lewis
Tim Lewis asked
Last Modified: 2019-03-01

I need to set QOS on my Cisco switches for a new UCASS phone system.  I have not used QOS before and want to make sure I do it correctly.   The phones will be on their own VLAN so I am not sure if I can set this at a level that everything on that VLAN uses this QOS.    What I need to set is DSCP 46 and L2P 5.  and will this need to be set on all switches or just the ones that the phones physically plug into.  Thank you for any assistance you can provide.
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Tim LewisNetwork Manager


Here is the full scope of what I need.  I want to have the phone plug into the port on the switch and connect to VLAN 15 and the PC connect into the phone and use the native vlan.   Below is what is required from the phone vendor.  Hope this helps.

Voice VLAN
We also require CDP/LLDP on the switches to assign the telephone endpoints to the proper Voice VLAN. All switch ports should be configured to Trust DSCP
Voice QOS
DSCP 46 and L2P 5 are default. DSCP 46 tags the packet with (EF) Expedited Forwarding. We also tag layer 2 priority with 5, the Layer 2 protocol is typically 5 for Cisco Auto QOS, for HP and others it is typically 6. . All WAN interfaces should have bandwidth reserved for EF traffic based on customer needs.
atlas_shudderedSr. Network Engineer

Tim - believe it or not, the switches are the easier part.  If all you are doing is configuring for voice you can use the auto configuration option on the access ports.

Where things are going to start getting sticky is as you are pushing traffic up the infrastructure onto layer 3 interfaces and out intra-site.  Are you installing to just one site or multiple?  Are you pinning the voice solution locally or is it going to be a cloud managed?
Tim LewisNetwork Manager


There will be multiple sites.  They will be going out through our SDwan system that the provider is using MPLS on to their hosted data center
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atlas_shudderedSr. Network Engineer

Okay, so the intrasite is going to be the challenge.  Especially with it being SD-WAN.  Since the packets are all encapsulated over the wide area then you will most likely be best effort.  Some SD-WAN manufacturers will mark/tag the external l3 header for priority but that will really only do you any good if you are going over mpls with honored tagging.
atlas_shudderedSr. Network Engineer

Any of your outbound/out of local calls (calls placed to another organization) will traverse the provider MPLS.  Any internal calls will want to run site to site direct.

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