Routers and Switches and Hubs, Oh My!

March 2001

Routers and Switches and Hubs, Oh My!

Initial HP 3000 hardware networking can be like a trip down a Yellow Brick Road

By Curtis Larsen

Auntie MAU! Auntie MAU! A Twisted Pair! A Twisted Pair!

A short while back, networks were as flat as the Kansas prairie, and computers on them were a lot like early prairie farmsteads: few and far between, pretty much speaking to each other only when they had to. (“Business looks good again this year.” “Yep.”) Most systems still used dumb terminals, and when speaking to anything outside the LAN, system-to-system modem connections were the way to do it.

A tornado named the Internet suddenly appeared in this landscape. It uprooted established standards and practices, swept aside protocols and speed limitations, and took us into a Technicolor networking landscape very different than what was there before.

Toto, I get the feeling our packets aren’t in Kansas anymore

Smaller companies were tossed before the tornado to eventually land and quickly begin growing again in the new environment. Large companies like IBM, HP, Digital, and Microsoft, who were rooted and established in their own proprietary standards (it sounds like an oxymoron, but it’s true) survived by generally ignoring the howling winds. Eventually, munchkin-like, they all came out to see what the general fuss was about, and found that a house-sized chunk of change (pun intended) had landed.

Networking, and the TCP/IP protocol had truly arrived in style, bringing strange new applications and markets. Serial connections and proprietary networking (“What do you mean we don’t need SNA to connect to the Wichita office anymore?”) gave way to a new kid on the block. And her little dog, too.

Follow the Yellow-Colored-Cable-and-Labeled-at-Both-Ends Road!

So here we are, sitting in a strange new networking land of strange new networking things. And for some of us, trying to understand the whole of it all — especially in relation to “legacy” system like the HP e3000 — is a little daunting. What are all these networking black boxes we plug the system into, and what do they all do? How can they make life better? (How can they make life worse?) If you’re not sure (or just plain curious) read on.

We’re off to see the wizard — this wonderful wizard of ours!

The networking wizard of your HP e3000 system is a program named “NMMGR.” It allows you to define networking hardware and tells you how to create connections with them. But what things can you define? Before we talk about connecting to things, we should probably take a crash-course in the things you’re connecting to.

Which path do I take? Well, you could take this one, that one, or both...

The basic networking boxes you’ll connect to are hubs, routers, switches, bridges, and gateways. Oh My. Let’s take them one at a time.

Since life is like an analogy, I’ll stretch one for the hub to go like this: If your network traffic is like water through a hose, then a hub is like a splitter, allowing multiple exits. Generally speaking, a hub simply splits the traffic from the “incoming” line into each connected port “out.” This is cheap and simple to set up if you don’t have a lot of connections, but like too many divisions on any hose, too many hubs will make the end connections anemic. The fewer connections the better, so most hubs have no more than 24 ports total.

Obviously, to make things better for all connections in larger networks, more “water pressure” was needed — and the switch was born.

Pay no attention to that man behind the curtain!

No, I’m not talking about the System Administrator. A switch looks very similar to a hub, but the appearance ends there. Again, if your network is like a stream of water in a hose, then your garden-variety switch is like a water tank, adding pressure to the line. Huge water tanks are placed at the heart of a city’s water system, while small tanks are placed on buildings. At the heart of most networks — tended by a cooing Network Administrator — is a core switch (the main tank).

Additional “work group” switches (building-sized tanks) can be used in wiring closets for special-need areas of the network. So, although a hub and a switch both offer multiple connections, the resulting “streams” have vastly different origin and force. Now that we’re one big speedy networking family, no one minds if it all fails, right? No? Well love can build a bridge, and so can electronics.

My Network’s crashing… What a world! What a world…

Having all your network connections on one physical segment isn’t too grand — especially when it fails. By segregating physical networks and then “bridging” them together, you ensure that in the face of adversity, some people can still laugh at the ones who can’t work. Aquariously speaking, a simple bridge is like a valved pipe between two water systems, passing water in both directions, and shutting one side’s valve if that system “loses pressure” (goes down). You say you want to route water based on content? Well then.

This here’s the ‘Packet of a Different Header’ you’ve heard about

Simply put, a basic router is an intelligent (logically) one-way bridge, examining network data information and very quickly sending data packets down one line or another. In our epic analogy, a router could be a thermal valve, forcing only cold water to flow this way, and hot water that way, preserving us from the heartbreak of tepidity. Since the router has to work quickly, it usually works at a lower level than other equipment does, caring less about content and more about destination. You say you’d like to exchange hot water with someone else? You’d like the gate to swing both ways?

There’s no place like the home network! No place like the home network…

A router is excellent at sending packets from Here to There (and not necessarily Back Again), but nothing beats the gateway for two-way communication. A gateway takes data from one network and sends it to another, even re-creating the data packet on the other side, if need be. To stretch our analogy to its limits, we could say that two different water systems exist, having the same characteristics, including temperature. One system is chlorinated, while the other is not, and so simply allowing the water to pass unmolested would be an issue — one system would become diluted, and the other exposed. What we need is a filtration pump that allows the water to be pumped in either direction, adding chlorine one way, and taking it out in the other direction.

Connecting to the Internet requires a gateway, since your home network doesn’t “know” how to reach something out there. What it does know is how to hand off a data packet destined for “Not Here” to a gateway for processing. The gateway in turns checks the packet’s address and sends it to the best possible network closer to the packet’s Ultimate Destination, re-labeling the packet as it does so, and putting its own address in the packet’s “return address.” If the packet’s Ultimate Destination isn’t on the new network either, then the gateway there does the same thing until the packet finally hits the Emerald City.

On its way back home, because of all the “return addresses” it picked up, the packet passes back through each gateway that it came from until, clicking its little ruby slippers, the packet realizes it is in no place but home.

Because of its intensive examination work, a gateway is almost always dedicated to its task, especially on larger networks. It was the gateway’s filtering abilities that led to using them as a firewall to protect networks by purposefully filtering and/or denying different types of connections and data. But the firewall is a topic all its own — just make sure you use one!

And you were there, and you, and you.
Oh Auntie Carly, there’s no place like HP!

So there you have it — Networking Devices 101. Now that you know what you can connect your e3000 to, you can come up with some ideas on how to use them, and answer questions about what to connect to. Should an e3000 be connected to a hub, or to a switch? (Switch!) Does a printer need to be connected to a hub or a switch? (A hub will usually be fine.) Should I use my e3000 as a gateway? (I think not.) Should the physical part of my network the e3000 is on be bridged? (Yes.) Can I configure a gateway and connect my e3000 to the Internet? (Certainly. But make sure you have a firewall first!) Can I use other protocols or connections besides TCP/IP and Ethernet? (Absolutely! X.25, SNA, FDDI, and a number of other connections are available, but they change a lot, so check with your favorite sales rep first.)

So long as HP continues to expand and extend the capabilities of their workhorse system, the e3000 will continue to be the perfect business computer choice. As everyone who uses and loves it knows – stick with it and your business just keeps flowing along, leaving your competitors all wet.

Curtis Larsen has been working with HP 3000s for over 10 years, and believes that, given enough time, any application can be written using the CI. He currently works for Covance Laboratories, in Madison, Wis.