IronPort Systems 4108GL - Manual (Page 333)

14-27
Port-Based Virtual LANs (VLANs) and GVRP
Port-Based Virtual LANs (Static VLANs)
P
o
rt
-Ba
sed V
ir
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LANs
(VLANs)
a
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G
V
RP
To summarize:
Effect of VLANs on Other Switch Features
Spanning Tree Protocol Operation with VLANs
Because the Switch 4108GL follows the 802.1Q VLAN recommendation to use
single-instance spanning tree, STP operates across all ports on the switch
(regardless of VLAN assignments) instead of on a per-VLAN basis. This means
that if redundant physical links exist between the switch and another 802.1Q
device, all but one link will be blocked, regardless of whether the redundant
links are in separate VLANs. However, you can use port trunking to prevent
STP from unnecessarily blocking ports (and to improve overall network
performance). Refer to “STP Operation with 802.1Q VLANs” on page 16-12.
Note that STP operates differently in different devices. For example, in the
(non-802.1Q) HP Switch 2000 and the HP Switch 800T, STP operates on a per-
VLAN basis, allowing redundant physical links as long as they are in separate
VLANs.
IP Interfaces
There is a one-to-one relationship between a VLAN and an IP network inter-
face. Since the VLAN is defined by a group of ports, the state (up/down) of
those ports determines the state of the IP network interface associated with
that VLAN. When a VLAN comes up because one or more of its ports is up, the
IP interface for that VLAN is also activated. Likewise, when a VLAN is
deactivated because all of its ports are down, the corresponding IP interface
is also deactivated.
VLANs Per
Port Tagging Scheme
1 Untagged or Tagged. If the device connected to the port is 802.1Q-compliant,
then the recommended choice is “Tagged”.
2 or More 1 VLAN Untagged; all others Tagged
or
All VLANs Tagged
A given VLAN must have the same VID on any 802.1Q-compliant device in which the VLAN is
configured.
The ports connecting two 802.1Q devices should have identical VLAN configurations, as
shown for ports X2 and Y5, above.