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qos on untagged switch ports

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qos on untagged switch ports


Another quick question.

I have a 5400 at the core of my network. It is set as the default gateway for all vlans. ANything destined for the WAN is routed out to a cisco 2811 router.

THe cisco 2811 is currently plugged into an untagged port in a completely separate vlan. I did this to keep broadcast traffic away from the cisco 2811 wan router.

The 5400 has qos policies applied to vlans (for voice). I have been reading that the qos policies get dropped on untagged ports.

DOes this mean that I am currently losing my qos controls on the link between the 5400 switch and the 2811 router?

How should I best fix this?

Should I make the switch to router link a trunk?

Matt Hobbs
Honored Contributor

Re: qos on untagged switch ports

When going across a WAN or an untagged link, your 802.1p settings no longer apply since they rely on 802.1Q VLAN tagging.

To prioritise traffic when not using tagging you need to use DSCP which inserts priority information into the IP packet itself.

You also need to configure mappings between 802.1p and DSCP for the prioritisation to work end to end. Fortunately this can be achieved on the 5400's - you will also need to configure the 2811 to recognise this traffic and put it in a low latency queue.

Re: qos on untagged switch ports

Hi Matt.

I have the following in the switch config at the moment (irrelevant details removed):

qos dscp-map 101100 name "VOICE"
qos dscp-map 101100 priority 6
qos type-of-service diff-services

vlan 1

vlan 144
name "VOICE"
qos priority 6

vlan 141
name "WAN"

vlan 148
name "DATA"
qos priority 0

Is this all that is needed? Does the QoS DCSP map work both ways (ie when entering the switch DSCP-->802.1p and when leaving the switch 802.1p --> DSCP)?
Matt Hobbs
Honored Contributor

Re: qos on untagged switch ports

From there, I think all you really need to add on the 5400 is

5400(config)# vlan 144 qos dscp 101100

All incoming voice packets will then have DSCP 101100 inserted into their headers (which the 2811 will need to be looking out for).

Re: qos on untagged switch ports

Once again Matt, many thanks.
At the moment I am identifying traffic for LLQ by port numbers, but being able to identify by DSCP as well will go a long way.

mack ragan_1
Occasional Contributor

Re: qos on untagged switch ports


Since he already has the mapping between 101100 and priority 6, could he just use "vlan 144 qos dscp 101100" and remove the priority 6 command?
Matt Hobbs
Honored Contributor

Re: qos on untagged switch ports

When you use the 'vlan 144 qos dscp 101100' command, it will automatically remove the 'qos priority 6' and replace it with 'qos dscp 101100' instead - which is mapped to priority 6. With that set I believe it should insert the DSCP code, and set the 802.1p bit if travelling out a tagged VLAN.