Blog

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

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

QoS requirements and recommendations for data traffic:

Best Effort

• Traffic should be marked to DSCP 0.
• Adequate bandwidth should be assigned to this class because majority of applications default to this class. Recommended is to set aside 25 percent for this class.

Bulk

• Traffic should be marked to DSCP AF11; excess traffic can be marked down by a policer to AF12 or AF13.
• Traffic should have a moderate bandwidth guarantee but should be constrained from dominating a link.

Transactional or Interactive

• Traffic should be marked to DSCP AF21; excess traffic can be marked down by a policer to AF22 or AF23.
• Traffic should have an adequate bandwidth guarantee for the interactive, foreground operations that it supports.

Mission Critical

• Traffic should be marked to DSCP AF31; excess traffic can be marked down by a policer to AF32 or AF33.
• Traffic should have an adequate bandwidth guarantee for the interactive, foreground operations that it supports.

QoS requirements and recommendations for control plane:

Network Management

• Traffic should be marked to DSCP CS2.
• Network Management applications should be protected explicitly with a minimal bandwidth guarantee.

Scavenger

• Traffic should be marked to DSCP CS1.
• Traffic should be assigned the lowest configurable queuing service; for instance, in Cisco IOS, this means assigning a CBWFQ of 1 percent.

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

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

Key QoS requirements and recommendations for interactive video (video conferencing) traffic:

• Interactive video traffic should be marked to DSCP AF41; excess video conferencing traffic can be marked down by a policer AF42 or AF43.
• Loss should be no more than 1 percent.
• One way latency should be no more than 150 ms.
• Jitter should be no more than 30 ms.
• Assign interactive video to either preferential queue or a second priority queue (when supported); when using Cisco IOS LLQ, overprovision the minimum priority bandwidth guarantee to the size of the video conferencing session plus 20 percent.

Key QoS requirements and recommendations for streaming video traffic:

• Streaming video should be marked to DSCP CS4, as designated by the QoS Baseline.
• Loss should be no more than 5 percent.
• Latency should be no more than 4 to 5 seconds (depending on the video application’s buffering capabilities).
• Guaranteed bandwidth (CBWFQ) requirements depend on the encoding format and rate of the video stream.
• Streaming video is typically unidirectional; therefore, remote branch routers might not require provisioning for streaming video traffic on their WAN or VPN edges (in the direction of branch to campus).
• Nonorganizational streaming video applications, such as entertainment video content, may be marked as scavenger (DSCP CS1), provisioned in the scavenger traffic class and assigned a minimal bandwidth (CBWFQ) percentage.

Reference

End-To-End QoS Network Design: Quality of Service in LANs, WANs, and VPNs

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.

Key QoS requirements and recommendations for call signaling traffic:

• Call signaling traffic should be marked as DSCP CS3 per the QoS Baseline (it can also be marked with the legacy value of DSCP AF31).
• 150 bps (plus Layer 2 overhead) per phone of guaranteed bandwidth is required for voice control traffic; more may be required, depending on the call signaling protocol.

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

Disclosure

NetworkJutsu.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.