Brocade Communications Systems 53-1002163-02 manual Frame classification incoming

Layer 2 Ethernet overview 1

Using MSTP, you can create multiple loop-free active topologies on a single physical topology. These loop-free topologies are mapped to a set of configurable VLANs. This enables you to better utilize the physical resources present in the network and achieve better load balancing of VLAN traffic.

For detailed information on configuring these protocols, see “Configuring STP, RSTP, and MSTP” on page 57.

Frame classification (incoming)

The Brocade FCoE hardware is capable of classifying incoming Ethernet frames based on the following criteria:

•Port number

•Protocol

•MAC address

The classified frames can be tagged with a VLAN ID or with 802.1p Ethernet priority. The 802.1p Ethernet priority tagging is done using the Layer 2 Class of Service (CoS). The 802.1p Ethernet priority is used to tag frames in a VLAN with a Layer 2 CoS to prioritize traffic in the VLAN. The Brocade FCoE hardware also accepts frames that have been tagged by an external device.

Frame classification options are as follows:

•VLAN ID and Layer 2 CoS by physical port number—With this option, the port is set to classify incoming frames to a preset VLAN ID and the Layer 2 CoS by the physical port number on the Brocade FCoE hardware.

•VLAN ID and Layer 2 CoS by LAG virtual port number—With this option, the port is set to classify incoming frames to a preset VLAN ID and Layer 2 CoS by the Link Aggregation Group (LAG) virtual port number.

•Layer 2 CoS mutation—With this option, the port is set to change the Layer 2 CoS setting by enabling the QoS mutation feature.

•Layer 2 CoS trust—With this option, the port is set to accept the Layer 2 CoS of incoming frames by enabling the QoS trust feature.

For detailed information on configuring QoS, see “Configuring QoS” on page 107.

Congestion control and queuing

The Brocade FCoE hardware supports several congestion control and queuing strategies. As an output queue approaches congestion, Random Early Detection (RED) is used to selectively and proactively drop frames to maintain maximum link utilization. Incoming frames are classified into priority queues based on the Layer 2 CoS setting of the incoming frame, or the possible rewriting of the Layer 2 CoS field based on the settings of the CEE port or VLAN.

The Brocade FCoE hardware supports a combination of two scheduling strategies to queue frames to the egress ports; Priority queuing, which is also referred to as strict priority, and Deficit Weighted Round Robin (DWRR) queuing.

The scheduling algorithms work on the eight traffic classes as specified in 802.1Qaz Enhanced Transmission Selection (ETS).

Converged Enhanced Ethernet Administrator’s Guide	5
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