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| 2.6 |  | VLAN Identification |
| 2.6.4 |  | The IEEE 802.10 protocol |

VLANs can be multiplexed across a FDDI backbone supporting the IEEE 802.10 protocol. Catalyst 5000 and 6000 family switches support 802.10 trunking.

FDDI interfaces that support 802.10 make selective forwarding decisions within a network domain based on a VLAN identifier. This VLAN identifier is the user-configurable 4-byte IEEE 802.10 Security Association Identifier (SAID). The SAID identifies traffic as belonging to a particular VLAN.

On a Catalyst 5000 or 6000, if a FDDI module receives a packet containing a VLAN SAID that maps to a locally supported Ethernet VLAN on the switch, the FDDI module translates the packet into Ethernet format and forwards it across the switch backplane to the Ethernet module. FDDI modules filter the packets they receive from reaching the backplane if the VLAN SAIDs in the packets do not map to a locally supported VLAN.

A SAID will be applied when a frame from an Ethernet VLAN needs to cross an FDDI backbone. Switch #1 must forward a packet from the Ethernet Module, Port 1, Slot 2, to the FDDI Module, Port 1, Slot 5. For this example, the translation of Ethernet VLAN 2 to FDDI VLAN 22 must be specified. The VLAN SAID must be identical on both FDDI modules. Because 802.10 FDDI interface links can also operate as ISL trunks, multiple VLAN translations can take place over a single link.

FDDI modules also support one native (nontrunk) VLAN, which handles all non-802.10 encapsulated FDDI traffic.