The second protocol is the GARP VLAN Registration Protocol (GVRP). GVRP is similar to GMRP, but instead of requesting admission to a multicast domain, the workstation requests admission to a particular VLAN. This protocol links 802.1p and 802.1Q standards. You can expect that they will be ushered in hand-in-hand when they are fin alized.

Knowing the Ins and Outs of VLANs After reviewing the types of VLANs available, you may wonder how competitors will ever agree on a standard. Fortunately, the standards body has divided traffic into three specific areas, allowing complex VLAN schemes to interoperate with ease.

· Ingress Port Each frame that reaches your switched network, whether from a router or a workstation, has a distinct source port. It is at this ingress that a VLAN decision must be made--will the switch accept the packet, and, if so, which VLAN will it place that packet on, for example. Making the decision at a single place in the network enables all sorts of fancy VLAN schemes to coexist. The switch makes one decision and tags the packet accordingly. Once the packet is on the network with a VLAN Identification Tag, it becomes Progress, or internal traffic.

· Progress Traffic Once a frame has been tagged with a VLAN identifier, it is switched through the network just like an untagged frame. All o f the decision-making has been done on the edge of the network, and it is no longer important how the frame entered the network. Assuming that the finalized standard doesn't change the maximum frame size (unlikely), the packet can be switched and routed through legacy equipment at the core of the network

· Egress Port Sooner or later, the frame must exit the switched network to reach a router or workstation. The egress device decides which port(s) to send the packet to and whether or not to strip out 802.1Q info. For example, a legacy workstation may not understand the 802.1Q VLAN information, but a multihomed server may want to receive and send VLAN information directly into the network, providing service to multiple subnets from a single interface. In addition, the ingress-progress-egress relationship enables vendors with proprietary VLAN implementations to build 802.1Q gateways for their products.

VLAN Road Map Many products today feature extensive VLAN capabilities. Some vendors cla im you will be able to upgrade their products, but be sure to read the fine print and ensure the product you are considering is on the list. If VLANs are part of your network road map, look for products that feature multiple VLANs on a single port, or those that claim 802.1Q upgradability.

The 802.1Q standard was slated for an April release. The remaining tension points in the standard revolve around managing the switch bridging table. If everything goes well, we'll see a working group ballot this November, with a rubber stamp sometime in 1998. Fortunately, the framing standard has been in place for more than a year and fast silicon-based solutions are in place today.

Another unanswered question is management. Each vendor has its own method of setting VLAN properties and distributing that information across the network. Much like you need multiple element managers to handle a mu ltivendor switched network, you will need multiple VLAN managers to manage your multivendor VLAN network.

Joel Cono ver can be reached at jconover@nwc.com.