Data Centre Bridging Capability Exchange Configuration
Overview
The Data Center Bridging Capability Exchange (DCBx) protocol extends the Link Layer Discovery Protocol (LLDP). It facilitates the exchange of Data Center Bridging (DCB) configuration parameters between directly connected devices, such as switches and network interface cards (NICs). DCBx enables automatic negotiation and configuration of DCB features to ensure consistent quality of service (QoS) and traffic prioritization across a network.
If LLDP is disabled on an interface, DCBX cannot operate on that interface. Attempting to enable DCBX on an interface where LLDP is disabled will result in a configuration commit failure.
DCBx plays a crucial role in modern data centers by enabling seamless configuration and interoperability between DCB-capable devices, ensuring efficient network performance.
Benefits
• Discovers the DCB capabilities of neighboring devices.
• Detects incorrect configurations or mismatches in DCB settings between peers.
• Configures DCB parameters on connected devices for interoperability.
Configuration
Configuring PFC parameter exchange typically involves enabling PFC mode, LLDP, activating DCBX, turning on PFC, and allowing the negotiation of control for each traffic priority (priorities 0–7).
Topology
The topology involves two switches SW1 and SW2 directly connected and enabled with DCBx and PFC.
PFC Configuration
Configuring DCBx for PFC via LLDP
The following procedure configures PFC parameters and sent them in LLDP messages.
1. Create bridge and enable DCB and PFC on SW1 and SW2.
bridge 1 protocol ieee vlan-bridge
data-center-bridging enable bridge
priority-flow-control enable bridge1
2. Set interface cd1/1 on SW1 and SW2 to layer 2 and bind it to bridge group.
interface cd1/1
switchport
bridge-group 1
3. Enable LLDP and DCBx on SW1 and SW2. Set LLDP for transmit and receive mode on the interface. Set the TLVs enabled for transmission on the interface to send an IEEE 802.1 organizationally specific TLV set in the packet.
!
lldp-agent
set lldp enable txrx
lldp tlv ieee-8021-org-specific data-center-bridging select
dcbx enable
!
4. Configure PFC on SW1 and SW2. Set the maximum number of priorities allowed for priority flow control on the interface. Enable PFC on priorities 0,1, and 2
!
priority-flow-control mode auto
priority-flow-control cap 3
priority-flow-control link-delay-allowance 65345
priority-flow-control enable priority 0 1 2
!
SW2.
!
priority-flow-control mode auto
priority-flow-control cap 6
priority-flow-control link-delay-allowance 5678
priority-flow-control enable priority 5 6 7
!
Validation
Verify DCBx and PFC status on SW1.
SW1#show priority-flow-control details interface cd1/1
bridge : 1
priority flow control : on
interface : cd1/1
Admin Configuration
--------------------
mode advertise willing cap link delay priorities
allowance
================================================================================
auto on on 3 65345 0 1 2
--------------------------------------------------------------------------------
Operational Configuration
-------------------------
state cap link delay priorities
allowance
================================================================================
on 6 65345 5 6 7
Verify DCBx and PFC status on SW2.
SW2#show priority-flow-control details interface cd1/1
bridge : 1
priority flow control : on
interface : cd1/1
Admin Configuration
--------------------
mode advertise willing cap link delay priorities
allowance
================================================================================
auto on on 6 5678 5 6 7
--------------------------------------------------------------------------------
Operational Configuration
-------------------------
state cap link delay priorities
allowance
================================================================================
on 6 5678 5 6 7
Verify Interface on SW1
SW1#show int cd1/1
Interface cd1/1
Flexport: Non Control Port (Active)
Hardware is ETH Current HW addr: 5c17.83f0.8523
Physical:5c17.83f0.8523 Logical:(not set)
Forward Error Correction (FEC) configured is Auto (default)
FEC operational status is off
Port Mode is access
Protected Mode is Promiscuous
Interface index: 5067
Metric 1 mtu 1500 duplex-full link-speed 10g
Debounce timer: disable
<UP,BROADCAST,RUNNING,ALLMULTI,MULTICAST>
VRF Binding: Not bound
DHCP client is disabled.
Last Flapped: 2025 Feb 25 16:54:32 (00:13:05 ago)
Load Interval: 300 seconds.
Statistics last cleared: 2025 Feb 25 16:54:32 (00:13:05 ago)
ND router advertisements are sent approximately every 0 seconds
ND next router advertisement due in 0 seconds.
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
5 minute input rate 16 bits/sec, 0 packets/sec
5 minute output rate 292 bits/sec, 0 packets/sec
RX
unicast packets 0 multicast packets 29 broadcast packets 0
input packets 29 bytes 1856
jumbo packets 0
undersize 0 oversize 0 CRC 0 fragments 0 jabbers 0
input error 0
input with dribble 0 input discard 0
Rx pause 0
TX
unicast packets 0 multicast packets 423 broadcast packets 0
output packets 423 bytes 29717
jumbo packets 0
output errors 0 collision 0 deferred 0 late collision 0
output discard 0
Tx pause 0
Verify Interface on SW2
SW2#show int cd1/1
Interface cd1/1
Flexport: Non Control Port (Active)
Hardware is ETH Current HW addr: 5c17.83ff.305f
Physical:5c17.83ff.305f Logical:(not set)
Forward Error Correction (FEC) configured is Auto (default)
FEC operational status is off
Port Mode is access
Protected Mode is Promiscuous
Interface index: 5035
Metric 1 mtu 1500 duplex-full link-speed 10g
Debounce timer: disable
<UP,BROADCAST,RUNNING,ALLMULTI,MULTICAST>
VRF Binding: Not bound
DHCP client is disabled.
Last Flapped: 2025 Feb 25 16:59:54 (00:13:49 ago)
Load Interval: 300 seconds.
Statistics last cleared: 2025 Feb 25 16:59:54 (00:13:49 ago)
ND router advertisements are sent approximately every 0 seconds
ND next router advertisement due in 0 seconds.
ND router advertisements live for 1800 seconds
Hosts use stateless autoconfig for addresses.
5 minute input rate 294 bits/sec, 0 packets/sec
5 minute output rate 17 bits/sec, 0 packets/sec
RX
unicast packets 0 multicast packets 446 broadcast packets 0
input packets 446 bytes 31279
jumbo packets 0
undersize 0 oversize 0 CRC 0 fragments 0 jabbers 0
input error 0
input with dribble 0 input discard 0
Rx pause 0
TX
unicast packets 0 multicast packets 31 broadcast packets 0
output packets 31 bytes 1984
jumbo packets 0
output errors 0 collision 0 deferred 0 late collision 0
output discard 0
Tx pause 0
lldp run
lldp tlv-select basic-mgmt system-name
lldp tlv-select ieee-8021-org-specific data-center-bridging
set lldp timer msg-tx-interval 5
lldp notification-interval 5
Note: To minimize the impact of PFC (Priority Flow Control) updates when operating in Auto mode via DCBx, this custom implementation ensures that PFC priority configurations remain consistent even during peer node reboots or interface flaps.
The mechanism locally caches the received DCBx PFC parameters and prevents unnecessary hardware resets of these values in the following scenarios:
When the LLDP session is re-established after such events, the node compares the newly received PFC parameters with the locally cached values:
The mechanism locally caches the received DCBx PFC parameters and prevents unnecessary hardware resets of these values in the following scenarios:
When the LLDP session is re-established after such events, the node compares the newly received PFC parameters with the locally cached values:
• Peer node reboot or power cycle.
• Peer node software upgrade or downgrade.
• Interface flap or fiber cut.
When the LLDP session is re-established after such events, the node compares the newly received PFC
parameters with the locally cached values:
parameters with the locally cached values:
• If no change is detected, the PFC configuration remains untouched, avoiding reapplication.
• If a difference is detected, the new parameters are applied to ensure proper PFC behavior.
This feature is enabled by default from release 6.6.1 and applies exclusively to nodes operating in PFC Auto mode, requiring no additional configuration.
Key Benefit:
• Minimized Traffic Disruption:
Maintains stable traffic flow with reduced packet loss and network instability during peer node restarts or interface disruptions.