Overview of Data Center Bridging (DCB)

Data center bridging is a set of features that enhances traditional Ethernet networks' abilities to manage traffic especially in environments where network traffic volume and transmission rates are high. Fiber channel can be dedicated to host this type of traffic. However, using dedicated links to service only fiber channel traffic can be costly. Thus, fiber channel traffic over Ethernet (FCoE) is more commonly used. DCB features address fiber channel's sensitivity to packet loss while traversing the Ethernet network.

DCB enables peers to distinguish traffic based on priorities. By distinguishing priorities, hosts can ensure that for traffic with higher priorities, packet integrity is preserved in cases of congestion between hosts. With the DCB exchange protocol (DCBX), communicating hosts can exchange configuration information that affect high speed network traffic. The peers can then negotiate on a common configuration that ensures continuous traffic flow while preventing packet loss for those packets with high priority.

In Oracle Solaris, LLDP is used to exchange DCBX TLV units. Provided that the underlying NIC supports DCB, DCB features such as priority-based flow control (PFC) and enhanced transmission selection (ETS) can be shared with peer hosts on the network.

• Priority-based flow control (PFC) prevents packet loss by implementing a mechanism that pauses traffic flow for packets with defined class of service (CoS) priority. See Priority-Based Flow Control. For more information about CoS, refer to the description of for the cos link property in the dladm(1M) man page.

• Enhanced transmission selection (ETS) enables bandwidth sharing among packets based on defined CoS priority. See Enhanced Transmission Selection.

As with all system information that is exchanged using LLDP, two types of DCB information exists on the host: local DCB information and remote DCB information. For PFC features to be effective, these two types of DCB information for PFC on the host must be symmetric. Typically, the local host must be able to match the DCB information it receives from the peer. In Oracle Solaris systems where DCB is enabled, this ability to synchronize DCB information with the peer is also enabled.

How to Enable DCBX

Support for DCBX is automatically enabled when you enable LLDP. This procedure provides alternative manual steps in case certain automatic processes fail. In the procedure, assume that the steps are implemented on net0.

1. Install the LLDP package.

   # pkg install lldp

2. Verify that the LLDP service is running.

   # svcs lldp

   If the LLDP service is disabled, start the service with the following command:

   # svcadm enable svc:/network/lldp:default

3. Ensure that the LLDP agent is running on Rx and Tx modes.

   # lldpadm show-agentprop -p mode net0

   If the LLDP agent is not enabled on both modes, type the following:

   # lldpadm set-agentprop -p mode=both net0

   For more information, see SMF Property for LLDP.

   For other possible configurations of the LLDP agents, see Enabling LLDP on the System.

4. Ensure that the underlying NIC supports DCB.

   # dladm show-linkprop -p ntcs net0

   A property value that is greater than zero (0) indicates that the NIC supports DCB.