QoS Layer 2 Marking
Ethernet 802.1Q/p
Switch (config-if)# mls qos 5 ! Sets 802.1Q CoS to 5 on outer frame Switch (config-if)# mls qos cos override ! Overrides any existing CoS value on the outer frame
Frame Relay Discard Eligible Bit
With Frame Relay, it uses 0 or 1 to mark the frame to indicate which one is more important. When it is marked with the value of 0 then it won’t be eligible to be dropped. When it is marked with the value of 1 then it would be eligible to be dropped when the network experiences congestion.
Router# sh run policy-map SET-FR-DE class OUT-OF-SLA set fr-de
ATM Cell-Loss Priority Bit
ATM has the same mechanism to drop frames when there’s network congestion.
Router# sh run policy-map SET-ATM-CLP class OUT-OF-SLA set atm-clp
MPLS Experimental Bits
MPLS is a tunneling protocol that uses labels to envelope an IP packet.
set mpls experimental imposition – Sets a specific value on all labels that are pushed onto the packet
set mpls experimental topmost – Sets a specific value only on the topmost MPLS label on the packet
References
Cisco QoS Exam Certification Guide (IP Telephony Self-Study) (2nd Edition)
End-to-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs
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