Networking: Making LAN Design More Intelligent
By Jim Metzler
April 15, 2008 —
I am very excited about this new newspaper in general and about this new column on networking in particular. This column is intended to present a high-level view of the networking industry, both in terms of the new products and services being offered in the marketplace, as well as how IT organizations are, or are not, using these products and services. The ultimate goal, of course, is to explain what all of this means to you the reader.
I’ll start off with a level setting in terms of networking. By that I mean that I will use the first two columns to present a high-level discussion of where we have come over the last decade or so and identify some of the key network issues of today. With that goal in mind, a simple, but powerful, way to classify networks is whether or not they are a Local Area Network (LAN) or a Wide Area Network (WAN). This classification works reasonably well. For example, people often refer to a Storage Area Network (SAN). In virtually all cases, a SAN is a special case of a LAN. People also refer to a remote access network, which is a special case of a WAN. One area in which the classification tends to break down is in discussing a Metropolitan Area Network (MAN). I will discuss MANs in a future column, so for now let’s stick with the approach that a network is either a LAN or a WAN. Having accepted that classification scheme, I will use this column to discuss how LANs have evolved and will use the next column to discuss how WANs have evolved.
As recently as a decade ago virtually all LANs were based on shared media. The use of shared media meant that any traffic on the LAN could interfere with all of the other traffic on the LAN—similar to what happens today on WiFi networks. That typically was not a problem when the utilization of the LAN was low. And utilization tended to be low for two key reasons. One reason was that not everybody had LAN connectivity. The second reason was that the predominant use of LANs at that time was for very simple print and file sharing of word documents. Very few people were shipping around large Powerpoint documents, and streaming media to the desktop was a concept, but not a reality.
In the mid 1990s, the most common LAN technology was shared Ethernet running at 10 megabits per second. However, other LAN technologies were also somewhat common, most notably the majority of financial organizations deployed LANs that were based on Token Ring technology from IBM. In addition, large organizations sometimes connected their workgroup LANs with FDDI (Fiber Distributed Data Interface), a shared LAN that ran at 100Mbits/sec.
Interesting insight into network evolution is provided by the fact that during the time when shared media LANs were the norm, articles were written about how it was not possible to exhaust the capacity of shared 10Mbits/sec Ethernet. The critical flaw in the reasoning of the authors who wrote those articles was that they assumed that the role of the LAN would not change—that it would always be there primarily to support simple print and file sharing. There is a key lesson learned from this. In particular, we typically can ride a network technology for a very long time. However, there comes a time when the demands on the network are such that it is time to migrate to a new technology. The trick, of course, is determining when is the correct time to shift to a new technology.
In the early 1990s, IT organizations began to deploy first generation LAN switches. The motivation was quite simple: the fewer users on a LAN segment, the less the users interfered with each other, and the greater the overall throughput. However, while IT organizations used these first generation LAN switches to reduce the number of users on a LAN segment, no IT organization at this time was dedicating a LAN switch port to individual users.
In the mid 1990s, a new version of Ethernet that ran at 100Mbits/sec was developed. This version of Ethernet is often referred to as Fast Ethernet. While it was possible to implement Fast Ethernet as a shared LAN, that never was very popular. Instead, most companies that implemented Fast Ethernet did so in a switched LAN environment.
At this time, Cisco was firmly established as the leading vendor of enterprise routers. To Cisco’s credit, they recognized that a major technology transition was underway and that IT organizations were shifting away from shared LANs and to switched LANs. Motivated to be a player in this new market, Cisco acquired a number of LAN switching companies, including Kalpana, Crescendo and Grand Junction.
The late 1990s saw the emergence of the Layer 3 switch, which offered a huge performance improvement over software-based backbone routers. During this time period the existing shared LAN hubs were phased out of wiring closets in favor of Layer 2 switches. This migration was accelerated by Y2K. In particular, many IT organizations used the threat of impending doom come Jan. 1, 2000 to get rid of a lot of their old networking gear. Today, the vast majority of LANs are based on some form of switched Ethernet.
From the beginning, switched LAN design has been about two things: availability and performance. As a result, the LAN switches that have been deployed have not been terribly intelligent. However, we are possibly at another inflection point relative to LAN design. Many vendors are now making the claim that more intelligence must be added to the LAN to support new demands such as enhanced security. Established vendors such as Cisco, HP and Enterasys are making this claim. In addition, at least one hot start-up company, ConSentry Networks, is also pushing this idea. One of the key challenges facing network organizations as they refresh their LANs is do they keep the same approach to LAN design (i.e., fast, reliable and dumb) or is this the time to shift to a new LAN design—one that includes more intelligence?
Jim Metzler has worked in just about every aspect of the networking industry in more than 30 years of professional experience. He can be reached at jim@ashtonmetzler.com.
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