Chapter 4: Examples
Switch 1 checks the Filtering Database for the MAC address of User B. User B’s MAC address is located, and Port 2 is identified as User B’s location. The frame is then checked for eligibility and frame format for Port 2. Since Port 2 is a 1Q Trunk port, it is eligible to transmit frames for all VLANs. The frame is tagged and transmitted out Port 2.
The switch also recognizes the MAC address of User B in its Source Address Table, FID 1, and updates that table to contain the MAC address and port combination of the Mail Server.
6.This tagged unicast frame is received by Switch 2. The frame is already tagged as belonging to the Default VLAN, so no classification needs to be done. The switch recognizes User B’s MAC address in its Source Address Table, FID 1, and updates that table to contain the Mail Server’s MAC address and port combination.
The switch checks the Filtering Database for the MAC address of User B. User B’s MAC address is located, and Port 2 is identified as the location of User B. The frame is checked for eligibility and frame format for Port 2. Since Port 2 is a 1Q Trunk port, it is eligible to transmit frames for all VLANs. The frame is tagged and transmitted out port 2.
7.Switch 4 receives the frame on its 1Q Trunk port, Port 4, and examines the frame’s Tag. The frame maintains its Default VLAN classification. The switch also refers to its Source Address Table, FID 1, to see if it can locate an entry for User B. User B is found to be located on Port 1. The switch also updates its Source Address Table, FID 1, with the port and MAC address combination for the Mail Server.
The switch examines the Filtering Database and locates the MAC address entry for User B and Port 1. The frame is then checked for eligibility and frame format for Port 1. As Port 1 is considered eligible to transmit to the Default VLAN, the frame is transmitted out Port 1 without a VLAN Tag.
8.Bridge 1 receives the frame and recognizes User B’s MAC address. The frame is forwarded to the correct port and the bridge’s Source Address Table is updated with an entry for the Mail Server’s MAC address. User B receives the Mail Server’s response. Any further unicast traffic between the Mail Server and User B will be handled in the same fashion by the switches in the network.
802.1Q VLAN User’s Guide |
