DCB Configuration Guide
After network convergence in a data center, three types of traffic exist: LAN traffic, SAN traffic, and IPC traffic, each with distinct QoS requirements:
- SAN traffic is highly sensitive to packet loss and requires in-order delivery of packets during transmission.
- LAN traffic allows packet loss and only requires Best Effort (BE) service from the network.
- IPC traffic (used for server-to-server communication) demands low latency. Data Center Bridging (DCB) is a set of IEEE 802.1 bridging enhancements that meet these QoS requirements by creating a lossless Ethernet infrastructure for converged data center networks.
DCB Fundamentals
DCB features primarily include PFC, ETS, and DCBX.
PFC
PFC (Priority-based Flow Control) consists of priority-based flow control and PFCWD (PFC Watchdog). For details, please refer to PFC in QoS configuration guide.
ETS
In a converged data center network, the coexistence of LAN, SAN, and IPC traffic imposes stringent QoS demands. For example:
- SAN traffic is sensitive to packet loss and requires ordered delivery.
- IPC traffic demands ultra-low latency for server communication.
- LAN traffic only requires Best Effort service, where packet loss and reordering can be handled by end hosts, minimizing network intervention. Traditional QoS mechanisms cannot meet these requirements. Enhanced Transmission Selection (ETS) addresses this by enabling flexible traffic scheduling for converged networks. ETS defines a priority-based processing model and bandwidth allocation model for endpoints and bridges in DCB environments. This allows differentiated services and bandwidth allocation for different traffic types.
- For scheduling details, please refer to Congestion Management.
- For priority mapping details, please refer to Queue and Priority Mapping.
DCBX
Data Center Bridging Exchange Protocol (DCBX) is a component of DCB. It operates in DCB environments to enable devices on both ends of a link to discover and exchange DCB configuration parameters, significantly reducing administrative overhead. Key DCBX Functions:
- Discover the DCB configuration of peer devices.
- Detect DCB configuration errors on peer devices.
- Configure DCB parameters on peer devices. DCBX Exchangeable Parameters:
- ETS scheduling and priority information
- PFC configurations DCBX uses LLDP (Link Layer Discovery Protocol) to exchange information. DCB configuration parameters are encapsulated into TLVs (Type-Length-Value fields) within LLDP frames, enabling automatic DCB parameter negotiation between devices.
Configure DCB
Configure PFC
Please refer to Configure PFC.
Configure PFCWD
Please refer to Configure PFCWD.
Configure ETS
Please refer to Configure QoS Priority Mapping and Configure QoS Schedule Policy.
Configure DCBX
NOTES:
- Before enabling DCBX, ensure LLDP is enabled.
- Interfaces with ETS configuration synchronization enabled must retain default configurations for scheduling and priority mapping.
Table 1 Configure DCBX
Purpose | Commands | Description |
|---|---|---|
Enter global configuration view | configure terminal | - |
Enter interface configuration view. | interface ethernet interface_name | - |
Enable DCBX | lldp dcbx enable | - |
Enable PFC configuration synchronization | lldp dcbx pfc-willing | - |
Enable ETS configuration synchronization | lldp dcbx ets-willing | - |
Display and Maintenance
PFC Information
Please refer to PFC Information.
PFCWD Information
Please refer to PFCWD Information.
ETS Information
Please refer to Diffserv Map Information and Policy Map Information.
DCBX Information
Table 2 DCBX Information
Purpose | Commands | Description |
|---|---|---|
Display DCBX Configuration and Status | show lldp dcbx | - |
Typical Configuration Example
- Networking Requirement In the data center network, two data center switches (Switch A and Switch B) are interconnected, under which servers are running storage traffic, IPC traffic (802.1p priority 7) and general data traffic; it is necessary to achieve no packet loss for storage traffic, low latency for ICP, and best effort forwarding for general traffic.
- Topology
- Configuration Roadmap
- Configure DCBX (Data Center Bridging Exchange Protocol) on Switch A to automatically negotiate DCB capabilities with peer devices at both ends of the link.
- Activate Priority-based Flow Control (PFC) on Switch A to ensure lossless transmission for storage traffic (e.g., SAN traffic).
- Set up Enhanced Transmission Selection (ETS) with priority mapping and scheduling policies. Ensure low latency for IPC traffic and guaranteed bandwidth allocation for storage traffic.
- Procedure
#Configure DCBX Switch A
sonic# configure
sonic(config)# interface ethernet 0/0
sonic(config-if-0/0)# lldp dcbx enableSwitch B
sonic# configure
sonic(config)# interface ethernet 0/0
sonic(config-if-0/0)# lldp dcbx enable
sonic(config-if-0/0)# lldp dcbx ets-willing
sonic(config-if-0/0)# lldp dcbx pfc-willing#Configure PFC Enable the PFC function for priority 3 queues. By default, the global PFC function is enabled, and the priority 3 queue has already enabled the PFC function, so this configuration step is omitted.
sonic# configure
sonic(config)# priority-flow-control enable3#Configure ETS Create priority mapping
sonic# configure
sonic(config)# diffserv-map type 8021p ets
sonic(config-diffservmap-ets)# 8021p 7 cos 7Create policy-map and bind diffserv-map
sonic# configure
sonic(config)# policy-map ets
sonic(config-pmap-ets)# set cos 8021p diffserv etsConfigure queue-scheduler
sonic(config-pmap-ets)# queue-scheduler queue-limit percent 40 queue 0
sonic(config-pmap-ets)# queue-scheduler priority queue 7Bind policy-map to interface
sonic# configure
sonic(config)# interface ethernet 0/0
sonic(config-if-0/0)# service-policy ets- Verify the Configuration
#PFC configure
sonic# show interface priority-flow-control
Interface Lossless priorities
----------- ---------------------
0/0 3,4
0/1 3,4
0/2 3,4
0/3 3,4
0/4 3,4
0/5 3,4
0/6 3,4
0/7 3,4
0/8 3,4
0/12 3,4
0/13 3,4
0/14 3,4
0/15 3,4
0/16 3,4
0/20 3,4
0/24 3,4
0/28 3,4
0/32 3,4
0/33 3,4
0/34 3,4
0/35 3,4
0/36 3,4
0/37 3,4
...#policy-map configure
sonic# show policy-map ets
！
policy-map ets
queue-scheduler priority queue 7
queue-scheduler queue-limit percent 40 queue 0
set cos dscp diffserv ets#diffserv-map configure
sonic# show diffserv-map type 8021p ets
Diffserv Map ets:
Type 8021p
from 7 to 7
#DCBX configure and status
sonic# show lldp dcbx
Interface ETS Willing PFC Willing ETS Accepted PFC Accepted
----------- ------------- ------------- -------------- --------------
0/0 True True False False