300-365 · Question #61
A downstream packet containing a DSCP value arrives at the WLC Ethernet interface from the wired source network. The WLC is configured for QoS WLAN 802.1p mapping. How does the WLC treat the CAPWAP…
The correct answer is C. The outer CAPWAP CoS is marked and capped while the inner DSCP maintains the original. When the WLC is configured for 802.1p QoS mapping, the outer CAPWAP header receives a CoS marking that is capped by the WLAN QoS policy while the original DSCP value is preserved inside the CAPWAP tunnel.
Question
A downstream packet containing a DSCP value arrives at the WLC Ethernet interface from the wired source network. The WLC is configured for QoS WLAN 802.1p mapping. How does the WLC treat the CAPWAP QoS marking when leaving the controller interface for the respective AP and final wireless client destination?
Options
- ANo outer CAPWAP or inner QoS tagging is applied.
- BNo outer CAPWAP QoS tag is applied, but the original DSCP is maintained inside CAPWAP.
- CThe outer CAPWAP CoS is marked and capped while the inner DSCP maintains the original
- DThe outer CAPWAP DHCP is marked and capped without any inner DSCP value.
How the community answered
(51 responses)- A8% (4)
- B31% (16)
- C47% (24)
- D14% (7)
Why each option
When the WLC is configured for 802.1p QoS mapping, the outer CAPWAP header receives a CoS marking that is capped by the WLAN QoS policy while the original DSCP value is preserved inside the CAPWAP tunnel.
This is incorrect because 802.1p mode explicitly causes the WLC to apply an outer CoS tag to the CAPWAP tunnel, so claiming no tagging is applied contradicts the configured mode.
Preserving the inner DSCP with no outer tag describes DSCP passthrough behavior, not 802.1p mapping mode, which does produce an outer CoS marking.
In 802.1p mapping mode, the WLC derives an 802.1p CoS value for the outer CAPWAP header from the incoming DSCP and caps it at the ceiling defined by the WLAN QoS profile, preventing upstream trust escalation. The original DSCP is left unmodified inside the CAPWAP encapsulation so the receiving AP and ultimately the wireless client can use the correct per-hop behavior.
The phrase 'outer CAPWAP DHCP' is not a valid QoS construct; the correct outer marking in this mode is a CoS (802.1p) field, and the description of the inner behavior is also inaccurate.
Concept tested: WLC CAPWAP QoS 802.1p CoS marking and capping
Source: https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-10/config-guide/b_cg810/qos.html
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