User's Manual

Table Of Contents
Users Manual of IGS-5225 series
175
Port Overlapping
Port overlapping can be used to allow access to commonly shared network resources among different VLAN groups, such as
file servers or printers. Note that if you implement VLANs which do not overlap, but still need to communicate, you can connect
them by enabled routing on this switch.
Untagged VLANs
Untagged (or static) VLANs are typically used to reduce broadcast traffic and to increase security. A group of network users
assigned to a VLAN form a broadcast domain that is separate from other VLANs configured on the switch. Packets are
forwarded only between ports that are designated for the same VLAN. Untagged VLANs can be used to manually isolate user
groups or subnets.
IEEE 802.1Q Tunneling (Q-in-Q)
IEEE 802.1Q Tunneling (Q-in-Q) is designed for service providers carrying traffic for multiple customers across their networks.
Q-in-Q tunneling is used to maintain customer-specific VLAN and Layer 2 protocol configurations even when different
customers use the same internal VLAN IDs. This is accomplished by inserting Service Provider VLAN (SPVLAN) tags into the
customer’s frames when they enter the service provider’s network, and then stripping the tags when the frames leave the
network.
A service provider’s customers may have specific requirements for their internal VLAN IDs and number of VLANs supported.
VLAN ranges required by different customers in the same service-provider network might easily overlap, and traffic passing
through the infrastructure might be mixed. Assigning a unique range of VLAN IDs to each customer would restrict customer
configurations, require intensive processing of VLAN mapping tables, and could easily exceed the maximum VLAN limit of
4096.