| Now that we've covered the basic idea of creating VLANs, let's look at some of the ways this is done. There are standards, and then there are proprietary solutions. When upgrading a network, you should consider several questions when it comes to implementing VLANs in your network: Does the switch support VLANs? Small switches you buy at the local computer store for home or small office don't. Medium to high-end switches used in a large network usually do. What is the port density of the switch? In a small computer room you might not have space for a large number of interconnected switches. Instead, switches with a larger number of ports can be a better choice. If you are using a chassis switch, how many cards can you plug into the chassis? Can you start out with just a few cards for your current needs, and then add port cards as your network expands? Do ports on the switch have LED indicator lights you can use to check for link connectivity and use, or do you have to rely on software to track down bad or misconfigured ports? Does the switch limit broadcast traffic to specific VLANs, or does it broadcast this traffic to all the virtual LANs on the switch? This might be desirable, or it might not, depending on your circumstances. Does the switch support multiple network speeds (that is, 10/100Mbps or Gigabit Ethernet speeds for high-end servers)? Does the switch support high-speed connections to other switches and routers? Although TCP/IP has for all practical purposes overtaken other LAN protocols, such as AppleTalk and IPX/SPX, as the network protocol of choice, does the switch support multiple protocols? If you have a multiprotocol environment, will the switch support creation of VLANs to separate these distinct protocols into separate virtual LANs? Is your equipment purchase going to be used for a short period (say, a year or two) or is it going to be used longer? If you're in this for the long haul and won't be able to replace expensive VLAN switches for a while, choose a vendor that's known for providing an easy upgrade path (such as a firmware or software upgrade for the switch), or choose one that adheres to a known standard so that you can simply add switches as your capacity needs grow. What management software is available for the switch? If you want to move a user from one VLAN to another, do you have to physically unplug the user from one switch port and reconnect him to another port? Or, as is more often the case, can you simply use the switch management software to reconfigure that user's port to become a member of another VLAN?
Although not as important as the considerations in the preceding list, some VLAN-aware switches enable you to associate a port with more than one VLAN. For example, in Figure 9.2 we created three distinct VLANs. However, VLAN 1 has a server and a printer as well as workstations configured within its boundaries. In some situations, it might be desirable for a server to be able to participate in more than one VLAN. In that case, you want to be able to specify that the switch port to which the server is connected be part of more than one VLAN. This would not give other computers in the separate VLANs access to other VLANs, but instead it would work in reverse, allowing members of different VLANs to establish sessions with a server, or perhaps a printer or another networked device, that is a member of more than one VLAN. |
