Administrator Guide

Asymmetric DCB parameters are exchanged between a DCBx-enabled port and a peer port without requiring that a peer
port and the local port use the same congured values for the congurations to be compatible. For example,
ETS uses an asymmetric exchange of parameters between DCBx peers.
Symmetric DCB parameters are exchanged between a DCBx-enabled port and a peer port but requires that each
congured parameter value be the same for the congurations in order to be compatible. For example, PFC
uses an symmetric exchange of parameters between DCBx peers.
Conguration Source Election
When an auto-upstream or auto-downstream port receives a DCB conguration from a peer, the port rst checks to see if there is
an active conguration source on the switch.
• If a conguration source already exists, the received peer conguration is checked against the local port conguration. If the
received conguration is compatible, the DCBx marks the port as DCBx-enabled. If the conguration received from the peer is
not compatible, a warning message is logged and the DCBx frame error counter is incremented. Although DCBx is operationally
disabled, the port keeps the peer link up and continues to exchange DCBx packets. If a compatible peer conguration is later
received, DCBx is enabled on the port.
• If there is no conguration source, a port may elect itself as the conguration source. A port may become the conguration
source if the following conditions exist:
– No other port is the conguration source.
– The port role is auto-upstream.
– The port is enabled with link up and DCBx enabled.
– The port has performed a DCBx exchange with a DCBx peer.
– The switch is capable of supporting the received DCB conguration values through either a symmetric or asymmetric
parameter exchange.
A newly elected conguration source propagates conguration changes received from a peer to the other auto-conguration ports.
Ports receiving auto-conguration information from the conguration source ignore their current settings and use the conguration
source information.
Propagation of DCB Information
When an auto-upstream or auto-downstream port receives a DCB conguration from a peer, the port acts as a DCBx client and
checks if a DCBx conguration source exists on the switch.
• If a conguration source is found, the received conguration is checked against the currently congured values that are internally
propagated by the conguration source. If the local conguration is compatible with the received conguration, the port is
enabled for DCBx operation and synchronization.
• If the conguration received from the peer is not compatible with the internally propagated conguration used by the
conguration source, the port is disabled as a client for DCBx operation and synchronization and a syslog error message is
generated. The port keeps the peer link up and continues to exchange DCBx packets. If a compatible conguration is later
received from the peer, the port is enabled for DCBx operation.
NOTE: When a conguration source is elected, all auto-upstream ports other than the conguration source are marked
as willing disabled . The internally propagated DCB conguration is refreshed on all auto-conguration ports and each
port may begin conguration negotiation with a DCBx peer again.
Auto-Detection of the DCBx Version
The Aggregator operates in auto-detection mode so that a DCBx port automatically detects the DCBx version on a peer port. Legacy
CIN and CEE versions are supported in addition to the standard IEEE version 2.5 DCBx.
A DCBx port detects a peer version after receiving a valid frame for that version. The local DCBx port recongures to operate with
the peer version and maintains the peer version on the link until one of the following conditions occurs:
• The switch reboots.
• The link is reset (goes down and up).
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Data Center Bridging (DCB)