Concept Guide

NOTE: Because DCBx TLV processing is best eort, it is possible that CIN frames may be processed when DCBx is congured to
operate in CEE mode and vice versa. In this case, the unrecognized TLVs cause the unrecognized TLV counter to increment, but
the frame is processed and is not discarded.
Legacy DCBx (CIN and CEE) supports the DCBx control state machine that is dened to maintain the sequence number and acknowledge
the number sent in the DCBx control TLVs.
DCBx Example
The following gure shows how to use DCBx.
The external 40GbE 40GbE ports on the base module (ports 33 and 37) of two switches are used for uplinks congured as DCBx auto-
upstream ports. The device 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 congured as auto-downstream ports.
On the S4048, PFC and ETS use DCBx to exchange link-level conguration with DCBx peer devices.
Figure 31. DCBx Sample Topology
DCBx Prerequisites and Restrictions
The following prerequisites and restrictions apply when you congure DCBx operation on a port:
• For DCBx, on a port interface, enable LLDP in both Send (TX) and Receive (RX) mode (the protocol lldp mode command; refer
to the example in
CONFIGURATION versus INTERFACE Congurations in the Link Layer Discovery Protocol (LLDP) chapter). If
multiple DCBx peer ports are detected on a local DCBx interface, LLDP is shut down.
• The CIN version of DCBx supports only PFC, ETS, and FCOE; it does not support iSCSI, backward congestion management (BCN),
logical link down (LLDF), and network interface virtualization (NIV).
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Data Center Bridging (DCB)