# Bandwidth vs Bandwidth Remaining

**URL:** https://forum.networklessons.com/t/bandwidth-vs-bandwidth-remaining/26597
**Category:** Lessons Discussion
**Created:** [May 4, 2022, 7:07pm UTC](https://forum.networklessons.com/t/bandwidth-vs-bandwidth-remaining/26597 "2022-05-04T19:07:45Z")
**Posts on this page:** 1
**Showing post:** 5

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### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis)
#### Post date: [September 21, 2022, 5:24am UTC](https://forum.networklessons.com/t/bandwidth-vs-bandwidth-remaining/26597/5 "2022-09-21T05:24:12Z")

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Hello José

> [@josanguapo](#):
>
> QoS can only be applied to trunks interfaces or to routed interfaces according to the folowing words from Lazaros in that section’s forum:

Yes, I see the confusion. Let me clarify my statement. QoS mechanisms that use DSCP and CoS values to make their decisions require that the DSCP and CoS information exists. For Layer 2 QoS, only tagged frames can participate in QoS because the CoS value exists within the tag. Therefore, only trunk ports (which use tagged frames) can apply Layer 2 QoS policies. For Layer 3 QoS where DSCP values are used, using a policy map as in this lesson, it is possible to queue packets with a particular priority based on the DSCP values found in the IP header. Typically, a Layer 2 port will not be able to “read” information in the Layer 3 header, however, there are switch models with the appropriate IOS that are able to read those Layer 3 DSCP values and queue accordingly.

> [@josanguapo](#):
>
> Another question: what’s the difference between the “priority” command used in the previous lesson and the “police rate” command used in the previous. Both assign the traffic to a LLQ up to a certain maximum per second, don’t they?

The `priority` command in the [QoS LLQ lesson](https://networklessons.com/quality-of-service/qos-llq-low-latency-queueing-cisco-ios) is used to define the priority queue within the LLQ scheme. Using that keyword makes all packets that match bypass the CBWFQ scheduler. The `police rate` command here is simply defining a rate at which to police traffic. However, the important thing here is that it is put under a `priority level` command. As shown below, the priority level command enables you to configure multiple priority queues. In this case, Rene has only created one, but it is essentially the same as using the priority command in the LLQ lesson.

> **[Cisco IOS Quality of Service Solutions Command Reference - N through P \[Support\]](https://www.cisco.com/c/en/us/td/docs/ios/qos/command/reference/qos_book/qos_n1.html#wp1049085)**

> [@josanguapo](#):
>
> Additionally, I’d like to point out 2 that I’ve detected a minor error: The sum “10 + 20 + 30 = 70 Mbps” is wrong. Those values sum 60, not 70.

Yes, thanks for that, I’ll let Rene know to make the correction.

I hope this has been helpful!

Laz

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