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New Member

Basic Qos question

We have 3 switches (old catalyst 3550's) at SITE A with the following:

TOP SWITCH

Has CUCM on Port 2 with QOS enabled. The switch has port 25 trunked to the middle switch

MIDDLE SWITCH

Has local IP phones on them with QOS enabled on each port. Port 26 is trunked to bottom switch

BOTTOM SWITCH

Has Port 2 connected to a 2900 router (trunk mode) which is then routed into an MPLS network with QOS provided on the MPLS network and lots of IP phones at different sites (SITES B-Z) which have a 2900 router/2960 switch.

Users are complaining about choppy, one way calls etc and looking at the configs on the trunks (switches & routers), I can't see anything about QOS on those ports. QOS is set on all access ports on the above switches but not on the trunk ports which seem strange to me.

So, should I add "mls qos trust dscp" on all trunk ports on switches and all interfaces on the routers (LAN/WAN) so that DSCP is trusted from IP phones at SITE B > CUCM (SITE A) > SITE Z phones?

Any pointers would be great as I'm scratching my head here with why it's only enabled on the access ports on the switches?

  • Voice over IP
3 REPLIES
Super Bronze

Re: Basic Qos question

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

 

Yes, normally you would want to trust your QoS marking on switch (infrastructure) trunk ports.  The difference with an edge port, you may do additional QoS marking validation that you wouldn't on an infrastructure port.  An exception might be a trunk port to an edge host.

Also for both edge ports and infrastructure ports, if transient congestion is possible, you might want egress QoS to prioritize more "important" traffic, e.g. VoIP.

BTW, mention of using a MPLS network - means there could be issues there (for end-to-end QoS policies).

New Member

Re: Basic Qos question

Thank you very much for confirming this. I have now trusted the trunks on all devices right up to the edge router and including the edge router trunk to the switch.

Another basic question here with regards to trunks. The traffic is coming off our mpls network marked with dscp ef.

It hits our router and the voice vlan is 100 whereas our data vlan is native vlan 1.

Now, from what I understand, the voice vlan is dot1q and can carry the dscp marking whereas the native vlan can't carry any marking as it's native. Is that right?

If so, is there any advantage to changing the native vlan from 1 to say dot1q vlan 10 for instance and just staying away from vlan 1?

Super Bronze

Re: Basic Qos question

Disclaimer

The   Author of this posting offers the information contained within this   posting without consideration and with the reader's understanding that   there's no implied or expressed suitability or fitness for any purpose.   Information provided is for informational purposes only and should not   be construed as rendering professional advice of any kind. Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In   no event shall Author be liable for any damages whatsoever (including,   without limitation, damages for loss of use, data or profit) arising  out  of the use or inability to use the posting's information even if  Author  has been advised of the possibility of such damage.

Posting

 

No, you're confusing L2 CoS, which requires VLAN tagged frames, with L3 packet's ToS DSCP.

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