Cisco Cisco 2504 Wireless Controller 技術マニュアル
On the wired side, Cisco routers and switches can operate on DSCP at layer 3 or CoS markings at layer 2.
The CoS markings are present in the 802.1p/q tag that is added to packets in order to mark the VLAN to
which the packet belongs. This 802.1q tag is 16 bits long; 12 bits are used for the VLAN ID (0 through
4095), one bit is not used, and three bits are used for CoS markings (0-7). Because CoS values 6 and 7 have
special significance on the wired network, Cisco does not send out the WMM values defined as 6, 5, 3, and 1
for platinum, gold, silver, and bronze. Instead, Cisco translates them into the CoS values of 5, 4, 0, and 1, as
shown in this table:
The CoS markings are present in the 802.1p/q tag that is added to packets in order to mark the VLAN to
which the packet belongs. This 802.1q tag is 16 bits long; 12 bits are used for the VLAN ID (0 through
4095), one bit is not used, and three bits are used for CoS markings (0-7). Because CoS values 6 and 7 have
special significance on the wired network, Cisco does not send out the WMM values defined as 6, 5, 3, and 1
for platinum, gold, silver, and bronze. Instead, Cisco translates them into the CoS values of 5, 4, 0, and 1, as
shown in this table:
Access Classh Quality of Service WMM Values Cisco-Translated CoS values
Voice
WMM Platinum
802.11e 6
802.1p 5
Video
WMM Gold
802.11e 5
802.1p 4
Best Effort
WMM Silver
802.11e 0
802.1p 0
Background
WMM Bronze
802.11e 1
802.1p 1
Wireless traffic that is associated with a higher priority QoS profile is given a higher priority tag on the wired
side. The CoS value assigned based on the WMM to 802.11e to 802.1q marking is maintained by both the AP
and the WLC so that the Control and Provisioning of Wireless Access Points (CAPWAP) packets are given
the same level of wired QoS as the packet, once the CAPWAP header is stripped off by the WLC and sent on
to the wired network.
side. The CoS value assigned based on the WMM to 802.11e to 802.1q marking is maintained by both the AP
and the WLC so that the Control and Provisioning of Wireless Access Points (CAPWAP) packets are given
the same level of wired QoS as the packet, once the CAPWAP header is stripped off by the WLC and sent on
to the wired network.
Similarly, traffic from the wired network that is in route to a wireless client has a CoS value associated with it
that Cisco copies to the CAPWAP packets that go to the AP. The AP then uses the CoS value in order to
determine the proper WMM queue to use.
that Cisco copies to the CAPWAP packets that go to the AP. The AP then uses the CoS value in order to
determine the proper WMM queue to use.
Tagged WLC Interfaces
It is common to leave the WLC Management Interface on an untagged/native VLAN. Because of the CoS
tagging discussed previously, this is not a wise choice if you enable 802.1p marking on the WLC. Without
that 802.1q tag, there is nowhere to put the CoS markings, and QoS fails on the Management Interface.
tagging discussed previously, this is not a wise choice if you enable 802.1p marking on the WLC. Without
that 802.1q tag, there is nowhere to put the CoS markings, and QoS fails on the Management Interface.
Even if you do not put any WLANs on the Management Interface, you might still encounter QoS issues with:
CAPWAP control packets sent by the WLC to its APs
•
Inner WLC communications
•
Backend authentication that originates from the Management Interface
•
Therefore, ensure all of your WLC interfaces are on tagged VLANs.
DSCP Recommendation
Due to the fact that more and more vendors use 802.1p-like markings over the air rather than the original
802.11e table (that is, voice is sent as 5 UP instead of 6), Cisco now recommends to trust DSCP end-to-end in
order to avoid confusion and mismatches. DSCP also offers more values and choices, is more resilient to
native VLANs, and is therefore more reliable to be preserved throughout the network.
802.11e table (that is, voice is sent as 5 UP instead of 6), Cisco now recommends to trust DSCP end-to-end in
order to avoid confusion and mismatches. DSCP also offers more values and choices, is more resilient to
native VLANs, and is therefore more reliable to be preserved throughout the network.
Post Release 7.2 Behavior Change
Before the WLC Release 7.2, there was no capping of the inner CAPWAP DSCP value. The first thing to
insist on is that the inner DSCP value did not change and is still not modified as of Release 8.1. So if an end
station (wireless or wired) sends a DSCP packet on a Gold (=video) WLAN, Gold marking between the AP
and WLC is enforced, but the original packet keeps its original DSCP tagging.
insist on is that the inner DSCP value did not change and is still not modified as of Release 8.1. So if an end
station (wireless or wired) sends a DSCP packet on a Gold (=video) WLAN, Gold marking between the AP
and WLC is enforced, but the original packet keeps its original DSCP tagging.