Brocade Communications Systems 53-1001761-01 manual Vlan tagging

1 Layer 2 Ethernet overview

The Brocade FCoE hardware handles Ethernet frames as follows:

•When the destination MAC address is not in the lookup table, the frame is flooded on all ports except the ingress port.

•When the destination MAC address is present in the lookup table, the frame is switched only to the correct egress port.

•When the destination MAC address is present in the lookup table, and the egress port is the same as the ingress port, the frame is dropped.

•If the Ethernet Frame Check Sequence (FCS) is incorrect, because the switch is in cut-through mode, a correctly formatted Ethernet frame is sent out with an incorrect FCS.

•If the Ethernet frame is too short, the frame is discarded and the error counter is incremented.

•If the Ethernet frame is too long, the frame is discarded and the error counter is incremented.

•Frames sent to a broadcast destination MAC address are flooded on all ports except the ingress port.

•When MAC address entries in the lookup table time out, they are removed. In this event, frame forwarding changes from unicast to flood.

•An existing MAC address entry in the lookup table is discarded when a device is moved to a new location. When a device is moved, the ingress frame from the new port causes the old lookup table entry to be discarded and the new entry inserted into the lookup table. Frame forwarding remains unicast to the new port.

•When the lookup table is full, new entries replace the oldest MAC addresses after the oldest MAC addresses age and time out. MAC addresses that still have traffic running are not timed out.

NOTE

New entries start replacing older entries when the lookup table reaches 90 percent of its 32k capacity.

VLAN tagging

The Brocade FCoE hardware handles VLAN tagging as follows:

•If the CEE port is configured to tag incoming frames with a single VLAN ID, then incoming frames that are untagged are tagged with the VLAN ID.

•If the CEE port is configured to tag incoming frames with multiple VLAN IDs, then incoming frames that are untagged are tagged with the correct VLAN ID based on the port setting.

•If the CEE port is configured to accept externally tagged frames, then incoming frames that are tagged with a VLAN ID are passed through unchanged.

NOTE

To make a VLAN FCoE-capable, you must enable the forwarding of FCoE traffic on the VLAN interface by entering the fcf forward CEE CLI command on the VLAN interface.

NOTE

Only a single switch-wide VLAN is capable of forwarding FCoE traffic.

For detailed information on configuring VLANs, see “Configuring VLANs Using the CEE CLI” on page 31.

4	Converged Enhanced Ethernet Administrator’s Guide
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