Static Virtual LANs (VLANs)
Multiple VLAN Considerations
tion on the location of the 5300xl changes over time. For this reason, the
8000M discards some packets directed through it for the 5300xl, 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 single-forwarding and multiple-forwarding database
devices, and configure the link with multiple, tagged VLANs.
Switch 8000M
VLAN 1
VLAN 2
5308L Switch
(Routing Enabled)
VLAN 1
VLAN 2
This switch has multiple
forwarding databases.
This switch has a single
forwarding database.
PC “A”
PC “B”
VLAN
1 & 2
VLAN
1 & 2
A1
C1
Figure 2-10. Example of a Solution for Single-Forwarding to Multiple-Forwarding
Database Devices in a Multiple VLAN Environment
Now, the 8000M forwarding database always lists the 5300xl MAC address on
port A1, and the 8000M will send traffic to either VLAN on the 5300xl.
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 a switch 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
2-5.) The fact that
the switches covered by this guide use the same MAC address on all VLAN
interfaces causes no problems.
■ 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:
2-20
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