Product Reviews

Burning Up the Wire

The affordable Cisco 3500 switch offers a GUI interface to IOS, Gigabit Ethernet support, and clustering capabilities. What more could a network engineer want?

What is it about the switch that makes it so much more desirable than the hub? Dividing a network into multiple collision domains doesn’t hurt and is the primary reason for purchasing switches. The fact that most switches are manageable means that you can baseline and track the impact of changes. Then there’s just something undeniably attractive about anything that has the capability to move data at a speed rated in gigabits.

The Cisco Systems Catalyst 3500 series of switches builds on the success of the older 3000 series of switches, but where the 3000’s biggest feature was the stack functionality—where you could control many switches through a single one—the 3500 adds another appealing feature, Gigabit Ethernet. Not only does the 3500 support Gigabit, but it also supports Full Duplex Gigabit Ethernet… over copper!

What Sets the 3500 Apart

What makes this switch different from any of Cisco’s other smaller switches, the 1900s and 2900s? Port densities don’t change; you can order up to 48 ports on an individual switch. Cisco has announced an 80-port model of the 2900 series, and while they haven’t done the same for the 3500s, I wouldn’t be surprised if they do by mid-summer.

If you’re familiar with Cisco’s other more economical switches, then you know that from a physical standpoint, the 2900 looks like a 1900 with some slots added to the top. The 3500 though is about as thick as a 1900 while offering the same number of ports as the 2900. The 2900 has an advantage here in that the A and B slots may be used for ATM and FDDI in addition to Gigabit Ethernet, while the extra slots on the 3500 may only be used for Gigabit.

Another major difference is the backplane capacity of the switches. At 3.2 gigabits per second, the 2900 series is almost as fast as a Catalyst 5500; but the 3500 series, at 10 gigabits per second, is three times faster. This higher capacity is very useful because it’s possible to configure a Gigabit EtherChannel circuit of four gigabits per second between two devices. You would do this by grouping both Gigabit ports together and running them to the same device on the other end.

Graphical Access

As a Cisco instructor, one of the biggest complaints I hear from beginning students is that Cisco’s IOS (Internetwork Operating System) is tough to learn; why doesn’t the company offer a GUI with their devices? Well, your prayers have been heard. While it doesn’t have capabilities on par with CiscoWorks 2000 (what do you expect for free?), the 3500 series switches do include a Web-based management graphical interface that’s surprisingly robust.

Let’s face it: Cisco’s IOS is extremely cryptic for those who aren’t used to it. Previously, the GUI Cisco had you use was a version of CiscoWorks, which is still available. Cisco now provides a Web-based GUI on the 3500 series switch that works with both Internet Explorer and Netscape Navigator. This interface can make completing basic tasks much easier, but it doesn’t eliminate the need to touch IOS. In order to be able to use the GUI, you need to configure the switch with an IP address; knowledge of how to complete this task in IOS is required, but you can learn it easily. Many of the more advanced tasks require configuration from the command line, and there are a few instances where the task may be supported in the GUI but only for certain versions of software.

A Look Inside

What is it about Gigabit Ethernet that has everyone wanting it? Oh, yeah, speed. The 3512, 3524, and 3548 come with two built-in gigabit slots in addition to their Fast Ethernet ports. The 3508 doesn’t have any Fast Ethernet ports; instead, it has eight gigabit slots. It’s not uncommon to see a closet of 3500s in a rack where you have seven 3524s running Fast Ethernet to the desktop, and then they’re connected together with the 3508, which also has Gigabit Ethernet to the data center or server room. You need to be aware of how Gigabit Ethernet works on these guys though in order to get the best throughput.

First, you need to decide how you want to connect two devices via Gigabit Ethernet. I’ll try to whittle your choice down by one. If the distance is more than one meter, then you can’t use copper. Note that the IEEE standard does provide for copper lengths of more than one meter, but Cisco requires proprietary cables. Now, you only have to choose between single-mode fiber and multi-mode fiber. The deciding factors here are how far you need to run cable and how much you’re willing to pay. The copper connectors are much cheaper than the single-mode fiber but fiber goes a lot farther than 1m. Make sure you purchase the correct GBIC (Gigabit Interface Converter) for your needs. If you plan on using the GBIC in a 2900, make sure you purchase a Gigabit Ethernet module as well, since the 2900XL doesn’t come with one.

You can connect two cables to each GBIC within the restriction for looping that the installation guide lists. This means that a 3512 may be connected via Gigabit Ethernet to four other switches, but when you do this, you only get half duplex connectivity. If you want full duplex, connect a single cable to the GBIC. The upshot here is that you have two gigabits of bandwidth to play with per Gigabit Ethernet port. You can split it between two switches or send it all to one, your choice. You may also channel the two ports by creating an EtherChannel port group. This would allow for four gigabits of bandwidth between two devices. I just want to know where the NIC is that will handle this! The statistics on each interface will show if one or both sides of the GBIC are in use. (See Figure 1.)

Figure 1. Cisco's 3500 switch gigabit interface. (Click on image to see larger version.)

One of the tasks supported from the GUI is troubleshooting. Assuming you can get to the switch via the GUI, then you have the option of selecting troubleshooting tools. “Show tech-support” is a command you’ll often use when talking to a TAC engineer (Figure 2). You also have the option to see interface information and log contents in addition to accessing the Visual Switch Manager.

Figure 2. The GUI and the "show tech-support" link. (Click on image to see larger version.)

Once in the Visual Switch Manager, the first thing you’ll notice is how clean everything is. The next thing is that you have no clue where anything is.

Click on the labels at the top of the page (port, system, security, and the like) to get a pull-down menu. (See Figure 3.)

Figure 3. A pull-down menu in the Visual Switch Manager. (Click on image to see larger version.)

From here, you can do many configuration tasks that would have you fumbling around in IOS. For example, say you want to enable SNMP on the switch. Click System | SNMP Configuration, and you can now configure SNMP. Click the “Enable SNMP” check box and click Apply. You’re then placed in a screen where you can configure SNMP Community Strings. (See Figure 4.)

Figure 4. Setting SNMP. (Click on image to see larger version.)

You can also see that the switch will automatically enable certain defaults such as Public for a Read Community String. Since Community Strings are pretty much the same as passwords when it comes to SNMP, this value should be changed when using SNMP.

Stacking Up

The 3500 is a direct descendent of the 3000 series switches but has undergone some amazing transitions in the last few years. One of the main features of the 3000 series switches was the ability to stack them into a single manageable device. The 3500s have retained this ability, and stacking, now called clustering, has also migrated to the 2900s and 1900s. This means you can have multiple devices in a rack and manage them from a single connection.

In order to activate the clustering, you have to designate a command switch. This is the device that will be in charge of the stack and that will replicate many global properties, like IP addressing, down to other switches in the cluster. Turning on clustering is a command line task; while you can configure the switch from either the console port or the browser window, you have to type the commands. (See Figure 5.)

Figure 5. Turning on a cluster from the IOS. (Click on image to see larger version.)

Once you have clustering turned on, you can get into Cluster Builder. Opening this window shows what devices are connected to the one you’re connected to (see Figure 6) but also opens a window called the “Suggested Candidate Window” (Figure 7). This is a list of devices that Cluster Builder has decided may join the stack if you wish. This makes it easy to add a switch to a rack then connect it to the cluster. Cisco even provides for a check box so you can prevent the Suggested Candidate Window from opening every time.

Figure 6. Cluster Builder. (Click on image to see larger version.)

Figure 7. The suggested candidate window. (Click on image to see larger version.)

Once you’ve created a cluster and added a second device to it, you can see that there’s only one IP address on the two devices (Figure 8), and that one is on device 3524. Device 3512 doesn’t have its own IP address anymore. Once the cluster is enabled, you may find it easier to manage the cluster from the Visual Switch Manager. Setting individual ports up is as easy as right-clicking on the port you wish to modify and then selecting the settings you want. Note that there’s a separate section for Virtual LAN modification.

Figure 8. A cluster of switches with a single IP address. (Click on image to see larger version.)

You can put a total of 16 devices into a cluster. Since this could be 15 80-port 2900 series switches and one 3548, you could have a theoretical maximum of 1,248 ports, all being managed from a single IP address. I haven’t found any information saying that there’s a maximum number of ports that a single IP address may manage.

One question I’m positive will appear in my mailbox is: “If you manage the switch cluster via one IP address and if I telnet to that IP address, I end up at the prime switch for the cluster; how do I configure a remote switch from the command line?” Worry not, young admin, Cisco has considered your plight and provided a solution. If you telnet to the management switch for a cluster and want to configure a port on another switch in that cluster, you need to know the cluster number of the switch you wish to configure. You can find this out by entering, “show cluster members”, on the main switch. Once you’ve found the number for the switch you want, enter the command, “rcommand #”, where # is the switch number.

Sweet and Sturdy

Overall, this is a sweet set of boxes. I liked the 2900 when it came out. The 3500 built on the success of the 2900 while still retaining the main capability that set the 3000s apart from the other switches, the clustering. If you think about it, 1,248 ports is a ton of ports—more than any organization I’ve ever seen needed in one closet. The 3500 has a robust backplane to provide for a massive amount of throughput at an economical cost. Costs will vary by vendor and purchase levels but a quick check on the Internet showed the 3512 available for $1,800. On the down side, this is still a complex device and will take time and effort to learn how to configure best to fit your organization. The graphical interface makes things a bit easier for the novice and a lot easier for someone already familiar with the workings of the device.

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