IBM 8275-416, User Manual

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Oversubscription of switch resources due to dynamic VLAN registration cannot be
predicted. Therefore, oversubscription will only be indicated during configuration if
the number of
statically included instances of port VLAN membership exceeds the
threshold of 310.
The following configuration example indicates an acceptable configuration for an
8275-416
with no feature modules :
Table 16. Acceptable VLAN configurations with no feature modules
Configuration Non-Default VLAN Port Instances
16 ports in Default VLAN (VLAN 1)* Not counted
16 ports each in 2 other VLANs * 32
10 ports each in 12 other VLANs 120
8 ports each in 16 other VLANs 128
9 ports each in 1 other VLAN 9
* Duplicate VLANs Total 289
As the Table 16 shows, port membership can be distributed in many ways across
many VLANs, and still not exceed the limits of the switch.
The two feature modules on the 8275-416 together have the same restrictions as
the base ports of the switch. The addition of feature modules does not increase the
number of non-Default VLAN port instances that can be supported by either the
base ports or the two feature modules together. However, the addition of feature
modules
does double the number of non-Default VLAN port instances that can be
supported across the entire switch, with 310 port instances distributed across the
base ports and 310 port instances distributed across the feature module slots.
The limitation only exist for the number of ports used in either the top or bottom of
the switch. There is
no
limitation using base ports and feature module ports in the
same VLAN.
Although duplicate VLAN configurations can waste switch resources, there are
some instances where they are useful. For instance, security concerns may be
addressed by having devices on the same LAN segments belonging to different
VLANs, but the VLANs having the same port membership. Another use for duplicate
VLAN configurations would be if a switch is placed in the core or in an intermediate
level of a network. The 8275-416 functions best as an edge device as opposed to
as a core switch.
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8275-416 User’s Guide