Enterasys Networks 802.1Q - Manual (Page 73)

Example 3, 1D Trunk Connection to 802.1Q VLAN Network
Examples 4-13
Figure 4-10 Switch 1 Forwards to 1D Trunk
5. The Mail Server receives the broadcast frame and recognizes it. The Mail Server responds with
a unicast frame to User B. This frame crosses the 1D Trunk and is received by Switch 1. Switch
1 classifies the unicast frame as belonging to the Default VLAN (the only membership for the
1D Trunk port).
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.
Floor 1
Floor 2
1 1
2
3
4
Mail Server
Green VLAN Green VLAN
Green, Inc.
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