Users Guide
Propagation of DCB Information
When an auto-upstream or auto-downstream port receives a DCB conguration from a peer, the port acts as a DCBx client and checks if a
DCBx conguration source exists on the switch.
• If a conguration source is found, the received conguration is checked against the currently congured values that are internally
propagated by the conguration source. If the local conguration is compatible with the received conguration, the port is enabled for
DCBx operation and synchronization.
• If the conguration received from the peer is not compatible with the internally propagated conguration used by the conguration
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 conguration is later received from the peer, the port is
enabled for DCBx operation.
NOTE: When a conguration source is elected, all auto-upstream ports other than the conguration source are marked as
willing
disabled
. The internally propagated DCB conguration is refreshed on all auto-conguration ports and each port may begin
conguration 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 recongures 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).
• The peer times out.
• Multiple peers are detected on the link.
DCBx operations on a port are performed according to the auto-congured DCBx version, including fast and slow transmit timers and
message formats. If a DCBx frame with a dierent version is received, a syslog message is generated and the peer version is recorded in
the peer status table. If the frame cannot be processed, it is discarded and the discard counter is incremented.
DCBx Example
The following gure shows how DCBx is used on an Aggregator installed in a Dell PowerEdge M I/O Aggregator chassis in which servers
are also installed.
The external 40GbE ports on the base module (ports 33 and 37) of two switches are used for uplinks congured as DCBx auto-upstream
ports. The Aggregator is connected to third-party, top-of-rack (ToR) switches through 40GbE uplinks. The ToR switches are part of a Fibre
Channel storage network.
The internal ports (ports 1-32) connected to the 10GbE backplane are congured as auto-downstream ports.
On the Aggregator, PFC and ETS use DCBx to exchange link-level conguration with DCBx peer devices.
Data Center Bridging (DCB)
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