Dell PowerConnect 3248 System User's Manual

Also see for PowerConnect 3248: Manual Features list Specification

Back to Contents PageVLANsDell™ PowerConnect™ 3248 Systems User's GuideVLANs and Frame TaggingVLAN ConfigurationAutomatic VLAN RegistrationVLAN ExamplesVLANs and Frame TaggingThe PowerConnect 3248 switch supports IEEE 802.1Q-compliant virtual LANs (VLANs). This capability provides a highly efficient architecture for establishingVLANs within a network and for controlling broadcast/ multicast traffic between workgroups. Central to this capability is an explicit frame tagging approach forcarrying VLAN information between interconnected network devices.With frame tagging, a four-byte data tag field is attached to frames that cross the network. The tag identifies to which VLAN the frame belongs. The tag maybe added to the frame by the end station itself or by a network device, such as a switch. In addition to VLAN information, the relative priority of the frame inthe network can be specified by the tag.VLANs provide greater network efficiency by reducing broadcast traffic, and they also allow you to make network changes without having to update IPaddresses or IP subnets. VLANs inherently provide a high level of network security, since traffic must pass through a Layer 3 switch or a router to reach adifferent VLAN.The PowerConnect 3248 switch supports the following VLAN features:l Up to 255 VLANs based on the IEEE 802.1Q standardl Distributed VLAN learning across multiple switches using explicit or implicit tagging and GVRP (GARP VLAN Registration Protocol)l Port overlapping, allowing a port to participate in multiple VLANsl End stations that can belong to multiple VLANsl Passing traffic between VLAN-aware and VLAN-unaware devicesl Four-level priority taggingl Link aggregation with VLANsVLAN ConfigurationBy default, VLAN operation on the switch is enabled. Therefore, all frames are transferred internally through the switch with a VLAN tag. This tag may alreadybe on the frame entering the switch, or added to the frame by the switch. VLAN information already existing on frames entering the switch is automaticallyhandled by the switch. The switch learns VLAN information from tagged frames and appropriately switches frames out the proper ports based on thisinformation. The configuration of VLANs for frames entering the switch without tags must be made by the user of the switch. This configuration can be madeeither through the web or console interface, or through Simple Network Management Protocol (SNMP).Assigning Ports to VLANsBefore enabling VLANs for the switch, you must first assign each port to the VLAN groups in which it will participate. By default, all ports are assigned to VLAN 1as untagged ports. You should add a tagged port (a port attached to a VLAN-aware device) if you want it to carry traffic for one or more VLANs and the deviceat the other end of the link also supports VLANs. Assign the port at the other end of the link to the same VLANs. However, if you want a port on this switch toparticipate in one or more VLANs and the device at the other end of the link does not support VLANs, you must add an untagged port (a port attached to aVLAN-unaware device).Port-based VLANs are tied to specific ports. The switch's forwarding determination is based on the destination MAC address and its associated port. Therefore,to make valid forwarding and flooding decisions, the switch learns the relationship of the MAC address to its related port (and to the VLAN) at run-time.VLAN ClassificationPackets that the switch receives are treated in the following ways:l When an untagged packet enters a port, the system automatically tags it with the port's default VLAN ID tag number. Each port has a default VLAN IDsetting that is user configurable. The default setting is 1. You can change the default VLAN ID setting for each port from the VLAN Port Settings page.l When a tagged packet enters a port, the default VLAN ID setting has no effect on the tag.¡ The packet proceeds to the VLAN specified by its VLAN ID tag number.¡ If the port in which the packet entered does not belong to the VLAN specified by the packet's VLAN ID tag, the system drops the packet.¡ If the port belongs to the VLAN specified by the packet's VLAN ID, the system can send the packet to other ports with the same VLAN ID.l Packets leaving the switch are either tagged or untagged depending on that port's membership properties.l In the VLAN Membership page, if a U is assigned to a port and VLAN, packets leaving the switch from that port and VLAN are untagged. If a T isassigned to a port and VLAN, packets leaving the switch from that port and VLAN are tagged with the respective ID for the VLAN to which that portNOTE: You can change port VLAN membership settings in the VLAN Membership page.