- play_arrow Basic CoS Configuration
- play_arrow CoS Overview
- play_arrow CoS on Interfaces
- play_arrow CoS Code-Point Aliases
- play_arrow CoS Classifiers
- Understanding CoS Classifiers
- Defining CoS BA Classifiers (DSCP, DSCP IPv6, IEEE 802.1p)
- Example: Configuring Classifiers
- Example: Configuring Unicast Classifiers
- Example: Configuring Multidestination (Multicast, Broadcast, DLF) Classifiers
- Understanding Host Inbound Traffic Classification
- Configuring a Global MPLS EXP Classifier
- Monitoring CoS Classifiers
- play_arrow CoS Rewrite Rules
- Understanding CoS Rewrite Rules
- Defining CoS Rewrite Rules
- Understanding Applying CoS Classifiers and Rewrite Rules to Interfaces
- Troubleshooting an Unexpected Rewrite Value
- Understanding CoS MPLS EXP Classifiers and Rewrite Rules
- Configuring Rewrite Rules for MPLS EXP Classifiers
- Monitoring CoS Rewrite Rules
- play_arrow CoS Forwarding Classes and Forwarding Class Sets
- Understanding CoS Forwarding Classes
- Defining CoS Forwarding Classes
- Forwarding Policy Options Overview
- Configuring CoS-Based Forwarding
- Example: Configuring CoS-Based Forwarding
- Example: Configuring Forwarding Classes
- Understanding CoS Forwarding Class Sets (Priority Groups)
- Defining CoS Forwarding Class Sets
- Example: Configuring Forwarding Class Sets
- Monitoring CoS Forwarding Classes
- play_arrow Lossless Traffic Flows, Ethernet PAUSE Flow Control, and PFC
- Understanding CoS IEEE 802.1p Priorities for Lossless Traffic Flows
- Configuring CoS PFC (Congestion Notification Profiles)
- Understanding CoS Flow Control (Ethernet PAUSE and PFC)
- Enabling and Disabling CoS Symmetric Ethernet PAUSE Flow Control
- Configuring CoS Asymmetric Ethernet PAUSE Flow Control
- Understanding PFC Functionality Across Layer 3 Interfaces
- Example: Configuring PFC Across Layer 3 Interfaces
- Understanding PFC Using DSCP at Layer 3 for Untagged Traffic
- Configuring DSCP-based PFC for Layer 3 Untagged Traffic
- play_arrow CoS and Host Outbound Traffic
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- play_arrow Weighted Random Early Detection (WRED) and Explicit Congestion Notification (ECN)
- play_arrow WRED and Drop Profiles
- play_arrow Explicit Congestion Notification (ECN)
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- play_arrow Data Center Bridging and Lossless FCoE
- play_arrow Data Center Bridging
- Understanding DCB Features and Requirements
- Understanding DCBX
- Configuring the DCBX Mode
- Configuring DCBX Autonegotiation
- Understanding DCBX Application Protocol TLV Exchange
- Defining an Application for DCBX Application Protocol TLV Exchange
- Configuring an Application Map for DCBX Application Protocol TLV Exchange
- Applying an Application Map to an Interface for DCBX Application Protocol TLV Exchange
- Example: Configuring DCBX Application Protocol TLV Exchange
- play_arrow Lossless FCoE
- Example: Configuring CoS PFC for FCoE Traffic
- Example: Configuring CoS for FCoE Transit Switch Traffic Across an MC-LAG
- Example: Configuring CoS Using ELS for FCoE Transit Switch Traffic Across an MC-LAG
- Example: Configuring Lossless FCoE Traffic When the Converged Ethernet Network Does Not Use IEEE 802.1p Priority 3 for FCoE Traffic (FCoE Transit Switch)
- Example: Configuring Two or More Lossless FCoE Priorities on the Same FCoE Transit Switch Interface
- Example: Configuring Two or More Lossless FCoE IEEE 802.1p Priorities on Different FCoE Transit Switch Interfaces
- Example: Configuring Lossless IEEE 802.1p Priorities on Ethernet Interfaces for Multiple Applications (FCoE and iSCSI)
- Troubleshooting Dropped FCoE Traffic
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- play_arrow CoS Buffers and the Shared Buffer Pool
- play_arrow CoS Buffers Overview
- play_arrow Shared Buffer Pool Examples
- Example: Recommended Configuration of the Shared Buffer Pool for Networks with Mostly Best-Effort Unicast Traffic
- Example: Recommended Configuration of the Shared Buffer Pool for Networks with Mostly Best-Effort Traffic on Links with Ethernet PAUSE Enabled
- Example: Recommended Configuration of the Shared Buffer Pool for Networks with Mostly Multicast Traffic
- Example: Recommended Configuration of the Shared Buffer Pool for Networks with Mostly Lossless Traffic
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- play_arrow CoS on EVPN VXLANs
- play_arrow Configuration Statements and Operational Commands
Troubleshooting Egress Bandwidth That Exceeds the Configured Minimum Bandwidth
Problem
Description
The guaranteed minimum bandwidth of a queue (forwarding class) or a priority group (forwarding class set) when measured at the egress port exceeds the guaranteed minimum bandwidth configured for the queue (transmit-rate) or for the priority group (guaranteed-rate).
On switches that support enhanced transmission selection (ETS) hierarchical scheduling, the switch allocates guaranteed minimum bandwidth first to a priority group using the guaranteed rate setting in the traffic control profile, and then allocates priority group minimum guaranteed bandwidth to forwarding classes in the priority group using the transmit rate setting in the queue scheduler.
On switches that support direct port scheduling, there is no scheduling hierarchy. The switch allocates port bandwidth to forwarding classes directly, using the transmit rate setting in the queue scheduler.
In this topic, if you are using direct port scheduling on your switch, ignore the references to priority groups and forwarding class sets (priority groups and forwarding class sets are only used for ETS hierarchical port scheduling). For direct port scheduling, only the transmit rate queue scheduler setting can cause the issue described in this topic.
Cause
When you configure bandwidth for a queue or a priority group, the switch accounts for the configured bandwidth as data only. The switch does not include the preamble and the interframe gap (IFG) associated with frames, so the switch does not account for the bandwidth consumed by the preamble and the IFG in its minimum bandwidth calculations.
The measured egress bandwidth can exceed the configured minimum bandwidth when small packet sizes (64 or 128 bytes) are transmitted because the preamble and the IFG are a larger percentage of the total traffic. For larger packet sizes, the preamble and IFG overhead are a small portion of the total traffic, and the effect on egress bandwidth is minor.
For ETS, the sum of the queue transmit rates in a priority group should not exceed the guaranteed rate for the priority group. (You cannot guarantee a minimum bandwidth for the queues that is greater than the minimum bandwidth guaranteed for the entire set of queues.)
For port scheduling, the sum of the queue transmit rates should not exceed the port bandwidth.
Solution
When you calculate the bandwidth requirements for queues and priority groups on which you expect a significant amount of traffic with small packet sizes, consider the transmit rate and the guaranteed rate as the minimum bandwidth for the data only. Add sufficient bandwidth to your calculations to account for the preamble and IFG so that the port bandwidth is sufficient to handle the combined minimum data rate and the preamble and IFG.
If the minimum bandwidth measured at the egress port exceeds the amount of bandwidth that you want to allocate to a queue or to a priority group, reduce the transmit rate for that queue and reduce the guaranteed rate of the priority group that contains the queue.
