D-Link DGS-3208TG User Guide - Page 31

Gigabit Ethernet Switch User's Guide The switch treats all ports in a trunk group as a single port. As such, trunk ports will not be blocked by the spanning tree algorithm. 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. Switches that use a load-balancing scheme that sends the packets of a host-to-host data stream over multiple trunk ports cannot have a trunk connection with the Switch. VLANs & MAC-based Broadcast Domains VLANs are a collection of users or switch ports grouped together in a secure, autonomous broadcast and multicast domain. The main purpose of setting up VLANs or a broadcast domain on a network is to limit the range and effects of broadcast packets. Two types of VLANs are implemented on the Switch: 802.1Q VLANs and port-based VLANs. MAC-based broadcast domains are a third option. Only one type of VLAN or broadcast domain can be active on the Switch at any given time, however. Thus, you will need to choose the type of VLAN or broadcast domain you wish to setup on your network and configure the Switch accordingly. 802.1Q VLANs support IEEE 802.1Q tagging, which enables them to span the entire network (assuming all switches on the network are IEEE 802.1Qcompliant). In contrast, MAC-based broadcast domains are limited to the Switch and devices directly connected to them. All VLANs allow a network to be segmented in order to reduce the size of broadcast domains. All broadcast, multicast, and unknown packets entering the Switch on a particular VLAN will only be forwarded to the stations or ports (802.1Q and port-based) that are members of that VLAN. 802.1Q and port-based VLANs also limit unicast packets to members of the VLAN, thus providing a degree of security to your network. Another benefit of 802.1Q and port-based VLANs is that you can change the network topology without physically moving stations or changing cable connections. Stations can be 'moved' to another VLAN and thus communicate with its members and share its resources, simply by changing the port 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. MAC-based broadcast domains, on the other hand, allow a station to be physically moved yet still belong to the same broadcast domain without having to change and configuration settings. The untagging feature of IEEE 802.1Q VLANs allows VLANs to work with legacy switches 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 (BPDU packets are not tagged). MAC-Based Broadcast Domains The Switch supports up to 12 MAC-based broadcast domains, which are by their nature, limited to the Switch itself and the devices connected directly to it. Since MAC addresses are hard-wired into a station's network interface card (NIC), MAC-based broadcast domains enable network managers to move a station to a different physical location on the network and have that station automatically retain its broadcast domain membership. This provides the network with a high degree of flexibility since even notebook PC's can plug into any available port on a network and communicate with the same people and use the same resources that have been allocated to the broadcast domain in which it is a member. Since MAC-based broadcast domains do not restrict the transmission of known unicast frames to other broadcast domains, they can only be used to define limited broadcast domains. As such, they are best 19