Data center bridging is used to manage the bandwidth, relative priority, and flow control of multiple traffic types when sharing the same network link, for example, when sharing a datalink between networking and storage protocols. Fibre channel can be dedicated to host this type of traffic. However, using dedicated links to service only fibre channel traffic can be costly. Therefore, fibre channel over Ethernet (FCoE) is more commonly used. DCB addresses the sensitivity of fibre channels to packet loss while traversing an Ethernet network.
DCB distinguishes traffic based on priorities, which are also called class of service (CoS) priorities. The host and the next hop use the DCB exchange protocol (DCBX) to negotiate a network configuration, such as no traffic loss and minimum bandwidth share, based on priorities. This process enables packets from different applications on the host and in the network to be treated according to their priorities and the corresponding configuration to be negotiated by using DCBX.
Each packet in a DCB network has a VLAN header that contains a DCB 3-bit priority value, which is a DCB priority. This IEEE 802.1p priority value differentiates each Ethernet packet in the network from the other packets. Depending on the priority values of the packets, you can configure DCB to allocate specific bandwidth to the packets. For example, all packets with a priority 1 must have PFC enabled and all packets with a priority 2 must have PFC disabled and a bandwidth share of 10%.
You can configure DCB features such as priority-based flow control (PFC) and enhanced transmission selection (ETS) based on priorities. For more information about PFC and ETS, see Priority-Based Flow Control and Enhanced Transmission Selection.
The DCB cos datalink property enables you to specify the CoS or priority of the datalink. The cos value that is set on a primary datalink does not apply to the VNICs that are created over this physical link. For information about customizing PFC based on the cos property, see Customizing Priority-Based Flow Control for DCB. For information about customizing ETS based on the cos property, see Customizing Enhanced Transmission Selection for DCB.
In Oracle Solaris, LLDP is used to exchange DCBX type-length-value (TLV) units. For more information about LLDP, see Chapter 5, Exchanging Network Connectivity Information With Link Layer Discovery Protocol. Provided that the underlying network interface card (NIC) supports DCB features such as priority-based flow control and enhanced transmission selection, configuration information for these features can be shared with peer hosts on the network, as follows:
PFC prevents packet loss by implementing a mechanism that pauses traffic flow for packets with a defined class of service (CoS). For more information about CoS, see the description of the cos link property in the dladm (1M) man page.
ETS enables bandwidth sharing among packets based on the defined CoS. See Enhanced Transmission Selection.