Cisco Cisco 2504 Wireless Controller 技術マニュアル
value correspond to the CoS.
With this system, you cannot have a mismatch, because one value is always rewritten in order to match the
other one (the trusted one). So, you can trust DSCP on access ports and CoS on trunk ports. The CoS value is
rewritten by the switch on egressing on a trunk port, even if the value was not present when ingressing from
an access port.
other one (the trusted one). So, you can trust DSCP on access ports and CoS on trunk ports. The CoS value is
rewritten by the switch on egressing on a trunk port, even if the value was not present when ingressing from
an access port.
As soon as you enter the mls qos command globally on a switch, the switch requires you to run the mls qos
trust cos
trust cos
or mls qos trust dscp command on switchports. If you do not, both CoS and DSCP values are
overwritten to 0. Without the global configuration from the mls qos command, any tag stays as is, but the
switch does not use priority queues at all.
switch does not use priority queues at all.
Different UP Markings for the Same Traffic Class
Voice is tagged as CoS 5 over a wired network, but as 6 on WMM/802.11e. This is often confused between
the 802.1p standard and the WMM standard. More and more vendors actually break the 802.11e/WMM
standard as they tag voice as UP 5 over the air (Microsoft with Lync is a famous example), so they basically
use the 802.1p table instead of 802.11e over the air. This is something to be aware of as Cisco still respects the
802.11e standard and tags voice as 6 over the air. This is another reason to trust DSCP over CoS.
the 802.1p standard and the WMM standard. More and more vendors actually break the 802.11e/WMM
standard as they tag voice as UP 5 over the air (Microsoft with Lync is a famous example), so they basically
use the 802.1p table instead of 802.11e over the air. This is something to be aware of as Cisco still respects the
802.11e standard and tags voice as 6 over the air. This is another reason to trust DSCP over CoS.
This is why, for added flexbility, the first maintenance release of the 8.1 WLC software adds the support of a
manual QoS map. This means that instead of using a static mapping table as before (for example, an UP of 5
will not be tagged as voice in the wired DSCP, but video instead), the administrator can decide to keep
trusting the original DSCP value. As such, for the most classic use case, you can decide to trust the DSCP EF
that a Microsoft Lync Windows clients will send and keep it tagged as voice rather than noticing it is sent
with UP 5 and downgrading it to a video DSCP over the network.
manual QoS map. This means that instead of using a static mapping table as before (for example, an UP of 5
will not be tagged as voice in the wired DSCP, but video instead), the administrator can decide to keep
trusting the original DSCP value. As such, for the most classic use case, you can decide to trust the DSCP EF
that a Microsoft Lync Windows clients will send and keep it tagged as voice rather than noticing it is sent
with UP 5 and downgrading it to a video DSCP over the network.
QoS Profiles
The first role of a WMM profile (platinum, gold, silver, bronze) is to set the ceiling (the maximum level of
QoS that clients are allowed to use). For example, if you set a silver profile on a WLAN, clients can send
background traffic or best effort traffic but are not allowed to send voice or video. If voice or video is sent,
they are treated like best effort.
QoS that clients are allowed to use). For example, if you set a silver profile on a WLAN, clients can send
background traffic or best effort traffic but are not allowed to send voice or video. If voice or video is sent,
they are treated like best effort.
Similarly, if you set platinum, the clients are allowed to use any QoS tag/class. That does not mean that
everything is considered as voice. It means that, if the laptop sends voice traffic, it is treated as such, and, if
the laptop sends best effort (as the majority of laptops send), it is also treated as best effort.
everything is considered as voice. It means that, if the laptop sends voice traffic, it is treated as such, and, if
the laptop sends best effort (as the majority of laptops send), it is also treated as best effort.
Another role of WMM profiles is to define the tag of non-QoS traffic. If WMM is set to allowed, clients are
still allowed to send non-QoS frames. Do not confuse two different situations:
still allowed to send non-QoS frames. Do not confuse two different situations:
If a laptop supports WMM (as the vast majority of laptops do) and sends QoS data frame, it uses a tag
of 0 if it is not tagging traffic.
of 0 if it is not tagging traffic.
•
If a laptop does not support WMM and sends simple data frames with no QoS field, the WLC
translates those data frames into the QoS profile. For example, data frames are translated as voice tags
if you configure platinum.
translates those data frames into the QoS profile. For example, data frames are translated as voice tags
if you configure platinum.
•
QoS profiles let you take the WMM values used in the wireless space and translate them into QoS marks on a
wired network. The configuration on the WLC uses the 802.11e-recommended mappings which are how
WMM is defined, such that Voice = Platinum = 6, Video = Gold = 5, Best Effort = Silver = 3, Background =
Bronze = 1.
wired network. The configuration on the WLC uses the 802.11e-recommended mappings which are how
WMM is defined, such that Voice = Platinum = 6, Video = Gold = 5, Best Effort = Silver = 3, Background =
Bronze = 1.