
Static Virtual LANs (VLANs)
Multiple VLAN Considerations
reason, the 6600 discards some packets directed through it for the 6120 switch, resulting in poor performance and the appearance of an intermittent or broken link.
The Solution. To avoid the preceding problem, use only one cable or port trunk between the
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| VLAN 1 |
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| VLAN |
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| VLAN 2 |
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| 1 & 2 |
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| PC “A” |
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| PC “B” | |||||||||||||||
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| A1 |
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| C1 |
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| This switch has a single | ||||||||||||||
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| forwarding database. | |||||||||||
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| VLAN |
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| VLAN 1 |
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| 1 & 2 |
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| VLAN 2 |
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| This switch has multiple | ||||||
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| 6120 Switch |
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| forwarding databases. | ||||||||||||||||
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Figure
Now, the 6600 forwarding database always lists the 6120 MAC address on port A1, and the 6600 will send traffic to either VLAN on the 6120.
To increase the network bandwidth of the connection between the devices, you can use a trunk of multiple physical links rather than a single physical link.
Multiple Forwarding Database Operation
If you want to connect one of the switches covered by this guide to another switch that has a multiple forwarding database, you can use either or both of the following connection options:
■A separate port or port trunk interface for each VLAN. This results in a forwarding database having multiple instances of the same MAC address with different VLAN IDs and port numbers. (See table
■The same port or port trunk interface for multiple (tagged) VLANs. This results in a forwarding database having multiple instances of the same MAC address with different VLAN IDs, but the same port number.
Allowing multiple entries of the same MAC address on different VLANs enables topologies such as the following: