Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

• Interfaces come up with DCB disabled and link-level flow control enabled to control data transmission between the Aggregator and other network devices (see Flow Control Using Ethernet Pause Frames). When DCB is disabled on an interface, PFC, and ETS are also disabled.
• When DCBx protocol packets are received, interfaces automatically enable DCB and disable link-level flow control.

DCB is required for PFC, ETS, DCBx, and FCoE initialization protocol (FIP) snooping to operate.

DCB processes VLAN-tagged packets and dot1p priority values. Untagged packets are treated with a dot1p priority of 0.

For DCB to operate effectively, ingress traffic is classified according to its dot1p priority so that it maps to different data queues. The dot1p-queue assignments used on an Aggregator are shown in Table 6-1 in dcb enable auto-detect on-next-reload Command Example QoS dot1p Traffic Classification and Queue Assignment.

The following example shows a default interface configuration with DCB disabled and link-level flow control enabled.

show interfaces Command Example: DCB disabled and Flow Control enabled

Dell#show running-config interface te 0/4
                                 !
                                 interface TenGigabitEthernet 0/4
                                 mtu 12000
                                 portmode hybrid
                                 switchport
                                 auto vlan
                                 flowcontrol rx on tx off
                                 dcb-map DCB_MAP_PFC_OFF
                                 !
                                 protocol lldp
                                 advertise management-tlv management-address system-name
                                 dcbx port-role auto-downstream
                                 no shutdown
                                 Dell#
                                 
                              

When DCB is Enabled When an interface receives a DCBx protocol packet, it automatically enables DCB and disables link-level flow control. The dcb-map and flow control configurations are removed as shown in the following example.

show interfaces Command Example: DCB enabled and Flow Control disabled

Dell#show running-config interface te 0/3
                                 !
                                 interface TenGigabitEthernet 0/3
                                 mtu 12000
                                 portmode hybrid
                                 switchport
                                 auto vlan
                                 !
                                 protocol lldp
                                 advertise management-tlv management-address system-name
                                 dcbx port-role auto-downstream
                                 no shutdown
                                 Dell#
                              

When no DCBx TLVs are received on a DCB-enabled interface for 180 seconds, DCB is automatically disabled and flow control is re-enabled.

Lossless Traffic Handling In auto-DCB-enable mode, Aggregator ports operate with the auto-detection of DCBx traffic. At any moment, some ports may operate with link-level flow control while others operate with DCB-based PFC enabled.

As a result, lossless traffic is ensured only if traffic ingresses on a PFC-enabled port and egresses on another PFC-enabled port.

Lossless traffic is not guaranteed when it is transmitted on a PFC-enabled port and received on a link-level flow control-enabled port, or transmitted on a link-level flow control-enabled port and received on a PFC-enabled port.

Enabling DCB on Next Reload To configure the Aggregator so that all interfaces come up with DCB enabled and flow control disabled, use the dcb enable on-next-reload command. Internal PFC buffers are automatically configured.

1. Globally enable DCB on all interfaces after next switch reload.

   CONFIGURATION mode

   dcb enable on-next-reload

To reconfigure the Aggregator so that all interfaces come up with DCB disabled and link-level flow control enabled, use the no dcb enable on-next-reload command. PFC buffer memory is automatically freed.

Enabling Auto-DCB-Enable Mode on Next Reload To configure the Aggregator so that all interfaces come up in auto-DCB-enable mode with DCB disabled and flow control enabled, use the dcb enable aut-detect on-next-reload command.

1. Globally enable auto-detection of DCBx and auto-enabling of DCB on all interfaces after switch reload.

   CONFIGURATION mode

   dcb enable auto-detect on-next-reload

Enabling DCB To configure the Aggregator so that all interfaces are DCB enabled and flow control disabled, use the dcb enable command.

Disabling DCB To configure the Aggregator so that all interfaces are DCB disabled and flow control enabled, use the no dcb enable command.

dcb enable auto-detect on-next-reload Command Example

Dell#dcb enable auto-detect on-next-reload