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Stackable NWay Ethernet Switch User’s Guide
Switch Management Concepts 35
Figure 5-3. Port trunking example
The switch treats all ports in a trunk group as a single port. As such, trunk ports will not be blocked by
Spanning Tree (unless a redundant link with higher STP priority is present).
Data transmitted to a specific host (destination address) will always be transmitted over the same port in a
trunk group. This allows packets in a data stream to arrive in the same order they were sent. A trunk
connection can be made with any other switch that maintains host-to-host data streams over a single trunk
port. A trunk connection cannot be made with switches that perform load-balancing on a per-packet basis.
VLAN
VLANs are a collection of switch ports grouped together in a secure, autonomous broadcast and multicast
domain. VLANs allow a network to be segmented in order to reduce the size of broadcast domains. All
Ethernet packets (unicast, broadcast, multicast, unknown, etc.) entering a VLAN will only be forwarded to the
ports that are members of that VLAN.
Another benefit of VLANs is that you can change the network topology without physically moving stations or
changing cable connections. Stations can be “moved” simply by changing VLAN settings from one VLAN (the
sales VLAN, for example) to another VLAN (the marketing VLAN). This allows VLANs to accommodate
network moves, changes, and additions with the utmost flexibility.
VLANs can also provide a level of security to your network. Port-based VLANs allow you to configure ports to
not send or receive packets outside of the VLAN.
The
untagging
feature of IEEE 802.1Q VLANs allow VLANs to work with legacy switches and NICs that don’t
recognize VLAN tags in packet headers. The
tagging
feature allows VLANs to span multiple 802.1Q-compliant
switches through a single physical connection and allows Spanning Tree to be enabled on all ports and work
normally.