Concept Guide

or iSCSI trac. In these scenarios, all network devices are DCBx-enabled (DCBx is enabled end-to-end). For more information about how
these features are implemented and used, refer to:
• Congure Enhanced Transmission Selection
DCBx supports the following versions: CIN, CEE, and IEEE2.5.
Prerequisite: For DCBx, enable LLDP on all DCB devices.
DCBx Operation
DCBx performs the following operations:
• Discovers DCB conguration (such as PFC and ETS) in a peer device.
• Detects DCB mis-conguration in a peer device; that is, when DCB features are not compatibly congured on a peer device and the
local switch. Mis-conguration detection is feature-specic because some DCB features support asymmetric conguration.
• Recongures a peer device with the DCB conguration from its conguration source if the peer device is willing to accept
conguration.
• Accepts the DCB conguration from a peer if a DCBx port is in “willing” mode to accept a peer’s DCB settings and then internally
propagates the received DCB conguration to its peer ports.
DCBx Port Roles
To enable the auto-conguration of DCBx-enabled ports and propagate DCB congurations learned from peer DCBx devices internally to
other switch ports, use the following DCBx port roles.
Auto-upstream
The port advertises its own conguration to DCBx peers and is willing to receive peer conguration. The port also
propagates its conguration to other ports on the switch.
The rst auto-upstream that is capable of receiving a peer conguration is elected as the conguration source. The
elected conguration source then internally propagates the conguration to other auto-upstream and auto-
downstream ports. A port that receives an internally propagated conguration overwrites its local conguration
with the new parameter values. When an auto-upstream port (besides the conguration source) receives and
overwrites its conguration with internally propagated information, one of the following actions is taken:
• If the peer conguration received is compatible with the internally propagated port conguration, the link with
the DCBx peer is enabled.
• If the received peer conguration is not compatible with the currently congured port conguration, the link
with the DCBx peer port is disabled and a syslog message for an incompatible conguration is generated. The
network administrator must then recongure the peer device so that it advertises a compatible DCB
conguration.
– The conguration received from a DCBx peer or from an internally propagated conguration is not stored in
the switch’s running conguration.
– On a DCBx port in an auto-upstream role, the PFC and application priority TLVs are enabled. ETS
recommend TLVs are disabled and ETS conguration TLVs are enabled.
Auto-downstream The port advertises its own conguration to DCBx peers but is not willing to receive remote peer conguration.
The port always accepts internally propagated congurations from a conguration source. An auto-downstream
port that receives an internally propagated conguration overwrites its local conguration with the new parameter
values.
296 Data Center Bridging (DCB)