Network Uptime

Years ago, life was much simpler on most LANs (insert harp music here). A single wire ran through the middle of the room, and every device on the network would communicate through this strand of copper. Using network management tools and protocol analyzers was simple, since connecting to the network at any point provided a view of every packet traversing the network.

LAN switches dramatically changed the world of protocol analysis. Suddenly, networks were taking this single wire in the room and effectively slicing it into hundreds of smaller pieces! It now became a search and rescue mission to manage the network, and finding the needle in this new haystack was a daunting task. LAN switch manufacturers weren't providing assistance, because most early LAN switches neglected network management capabilities in an effort to get their product to the market as quickly as possible.

LAN switches also removed an important network analysis requirement - connectivity to a physical port! File servers and workstations now connect directly to a switched port, with no interface available to connect an analysis tool into the middle of this single strand of copper or fiber.

Today, there are four major methods of connecting into a switched network:

* LAN Hub - For a half-duplex Ethernet connection, a hub can be placed between the workstation and the switch to provide a connection for the protocol analysis or network management device.

* Tap - Some manufacturers are creating stand-alone taps that provide an interface for an analysis tool. These taps have the advantage of supporting many different network topologies and media.

* 'Mirror' port - Many LAN switches have the ability to redirect traffic from one port to another, providing a 'mirror' for the protocol analyzer to use for access.

* Matrix switch - Enterprise networks use matrix switches to provide an electronic A-B switch to provide connectivity for the protocol analyzer. Matrix switches can also be controlled in-band and out-of-band, providing a good solution for analysis connectivity in remote locations.

Using a Hub to View a Switched Network

Although using a LAN hub to connect a protocol analyzer is limited to half-duplex LANs, and is one of the easiest and most effective ways to connect a monitoring tool to a switched network connection.

The most common use for a LAN hub is in an Ethernet environment. Most computer stores and networking catalogs have low-cost 10/100 Ethernet hubs for less than $50. Remember that you need to purchase a HUB, and not a SWITCH. It's this shared environment that provides visibility to the network analysis tools.

Almost any hub will work, and most engineers will choose a small hub with about four ports and a small power supply or 'cube.' For the analysts that travel, keep in mind that the power supply can be larger than the hub itself! You may need to look at many hub models until you find one that works best for your environment.

The hub doesn't require any special network management or configuration utilities. Don't worry that the hub won't provide SNMP management or auto-partitioning. This is a piece of hardware that will be used for a very specialized application, and additional bells-and-whistles aren't necessary.

Before using the hub, additional cables may be required to provide connectivity between the switch, the hub, and the network device. Some switches use Ethernet cross-over cables to provide end-station connectivity, and these cables won't work with a hub.

The integration of the hub between the LAN switch and the end-station requires disconnection of the current link, and the installation of the hub into the middle of the connection. In most cases this only takes a few seconds, but you should always be wary of disconnecting production equipment from the production network during working hours. If possible, install the hub during a maintenance downtime for later use.

Once the hub is in place, a network analysis tool can be connected to the hub to view communications between the LAN switch and the end-station. Since the analyzer doesn't communicate on the network, the hub is simply a passive 'listening post' for the analysis tool.

The advantages for using a hub are a low purchase cost, hubs are easy to use, and they install and uninstall quickly from the network. LAN hubs will only work in environments that run in half-duplex, you must break the connection to install and uninstall the hub, and they are good for analyzing a single station. This method can hardly be called Enterprise ready, but it's a great solution in the proper environment.

Using Network Taps to View a Switched Network

We've discussed using hubs to provide a look into a switched network, but the use of network 'taps' have been overlooked by most organizations. Like hubs, taps are put in place by breaking the network connection, and are placed into the network prior to problems occurring. Although copper taps are available, many taps in today's networking environments work with fiber.

Network taps are a great solution for environments that need immediate analyzer access to a switched device. These taps can also be located between switches, allowing an analyzer to gather information between major connections of the network.

In some environments, fiber splitters are a better choice for connectivity. Fiber splitters are similar to taps, but are completely passive (no power requirements). Fiber splitters also divide the light into two separate channels, which takes signal strength from one fiber and divides it into two (or more) fibers. When using a fiber splitter, make sure the 'light budget' allows for splitting a percentage of light from the main connection.

To find out more about network taps and fiber splitters, check out these web sites:

http://www.milan.com
http://www.amp.com/fiberoptics/pd.html
http://www.netoptics.com