Okay, I know little about networks. I know basically what a router and a hub do, and I know what type of cable to use for each situation. However, my Net+ training won't begin for a while, and I got a nice little hand-me-down from my office today: two 3Com "SuperStack II: Switch 3300" switches.



Would someone care to explain what these do? I've got some idea, but I don't know if it's correct. Will these be easy to switch with my hub on my current network?

after all the help you've been giving me .. i feel bad i can't help you with your problem... good luck

These are probably real switches. Home switches lack managibility and such, while this unit will probably allow you to select exactly what speed you want a specific port to run at, see complete traffic statistics, and more. Based on the "SuperStack" name, it probably also work well when used with a second switch of the same type, where they can be bound togther to work as one.

It should work fine as a normal switch at home as well. Benefits of these devices aren't really aparent except on large networks though.

These are probably real switches.

I've worked with this exact product in the past. Used them for the network backbone for a six-story office building using the fiber modules you can get for them.

Unless there's some nonstandard configuration on there, you should be able to drop them in in place of a hub.

Is your question ``What is a switch?''?

These are really nice switches to get given. Short of some technological breakthrough occuring that suddenly demands 1000BaseTX to the desktop, these switches will satisfy any home network for years to come. Or a small business. They are relatively small and lightweight too.

Networking 1.01.
You've probably heard of the OSI '7 layer' model. We're only concerned with layers 2 and 3 here. For reference, layer 1 is the Physical layer, that literally deals with how the bit stream is converted into electrical signals and moved from one place to the other. Layer 4 is the Transport layer, that deals with things like packet control and recovery, the TCP part of TCP/IP. We don't care at all about 5-7 in this discussion.

Layer 2 is the Data Link layer. This deals with converting packets of data into a raw datastream suitable for transmission by the physical layer. It also deals with MAC addresses, which are 'unique' hardware addresses assigned to network adapters. I quoted 'unique' because although by default every network adapter is set up with a unique MAC address that includes a manufacturer part and a serial number part, it is usually possible to override them in software. (In any decent OS anyway).
Layer 3 is the Network layer. This is the IP part of TCP/IP, where IP addresses live.

To try and clarify that all a bit further, lets 'demo' a couple of pings.

1) If you were to ping another machine on your network, your machines TCP stack ('Network'
- layer 3) would compare the IP address of the destination machine with your network IP address and subnet mask, and in doing so would realise that the destination was on the same network. At this point it would pass the packet to the layer 2 stack 'Data Link'. Assuming that you have just booted your machine and that it hasn't yet talked to the destination machine, you machine will send out an ARP discovery request, "arp who has destination_machine_IP tell my_IP". The destination machine will reply with it's MAC address, and then all intranet communcation will be handled layer2 <-> layer2 using MAC addresses only. Note that the destination MAC address will then be stored in an arp cache to speed things along in later communication.

2) Suppose instead that you ping a machine _not_ on your network. This time around when your machine compares the destination IP with its own IP address and subnet mask it will realise that the destination machine is on another network. Still in layer3, your machine will check it's routing table to see whether it knows about the destination network or whether it needs to follow the default route. Regardless, what it does next is essentially the same. It now sends the complete ping IP packet to the gateway or router that it just discovered. How does it do this? By using the same technique that it employed to talk to the local machine - It arps for the routers MAC address and then talks via layer 2 to it.

This is obviously simplified to hell, but hopefully should help you gain an understanding of what various network gear does.

A hub works only in layer 2. It simply rebroadcasts any layer2 communication to all the other ports on the hub, and monitors collisions. You can see why a hub soon gets flooded - if you have 10 machines on a 100BaseTX hub, then they have to share that bandwidth, ie 10Mbps each.

A 'domestic' switch is a bit more intelligent. It learns which MAC addresses are associated with each port, and only transmits data to the appropriate port. This means that (theoretically) each port could be communicating at 100Mbps simultaneously. Of course, in reality one of the ports is going to be a server or router connection that carries a large percentage of the data, but you see the point. Again, it only deals with layer2. It does not care 2 hoots about IP addresses.

A router typically deals in layer 3. It watches IP packets coming though it's ports, and routes them according to routing tables that have either been manually set up, or that have been discovered by automated routing protocols (such as BGP). It will have access control lists which will implement packet filtering based on IP addresses (simplistic firewalling)

So what do you have in you new gear?
You have a 'proper' switch. (Actually 2 of them). Essentially they do the same thing as a 'domestic' switch, operating in layer 2. But they have some really nifty tricks.
Firstly you can gang the Superstacks together. You need a 48port switch? You got it. You could add more (4 total = 96 ports IIRC).
You can tell the switch to lock down the ports to specific MAC addresses. If you're worried about someone installing a hidden open wireless router on an otherwise private LAN, this is useful.
You can segment the switch into separate VLANs. So you can tell it that ports 1-8 are on one LAN, and that 9-24 are on another. IIRC, you can define up to 16 VLANs on these switches. And you can VLAN across ganged switches obviously.
You can define ports as being important. This prioritizes their traffic over the switch backplane. Very useful for heavily used servers and routers.

One thing that these won't do is inter-VLAN routing. (Some big switches do). But who cares?

All the documentation for these is available here

You can segment the switch into separate VLANs. So you can tell it that ports 1-8 are on one LAN, and that 9-24 are on another. IIRC, you can define up to 16 VLANs on these switches. And you can VLAN across ganged switches obviously.

A few points:

1. First, if he isn't familiar with switches, he isn't familiar with VLANs.
   
   The idea is that a hub or a simple switch connects a series of computers together in one network. Each of those computers can talk directly to each other (at least on the Layer2 level, which, again, is all that a hub/switch deals with). VLANs allow you to separate out ports on your intelligent switch so that ports on VLAN1 can't talk directly to ports on VLAN2. It's as if there were multiple switches, but it's easier to deal with on a large network, as they're dynamically configurable. BTW, VLAN means Virtual LAN.
   
   
2. Second, the ports on a VLAN need not be contiguous. VLAN1 could contain ports 1,5,6,10, and 24 while VLAN2 could contain 2,3,4,7,and 20, for example.
   
   
3. Inter-VLAN routing means that it would turn your switch into a router. Exactly why you'd want to do this is unknown, as, generally, anyone that can afford real switches can afford a real router, and, generally, the software addon cost for the routing module for those switches that can do it costs almost as much as a router, anyway.

1) Yep, I should have explained that a bit better.
2) I decided not to complicate that part. It should be obvious in the documentation if he cares that much
3) Switch where you can, route where you must...I agree that the pricing of routing modules for most switches is exhorbitant, but it's kinda handy when you need to implement a new LAN in a hurry and you don't know who nicked the last 2500.

genixia~ BRAVO! What a wonderful and helpful post. That helps a lot, and I'll read it over a few times to make sure I understand it. When I start studying networking I'll have a good starting point.

Bitt~ thanks for the clarifications. I don't see myself needing a VLAN with the number of computers on this network, but it's nice to know about

gsm01320~ hehe, no problem. I wasn't giving that much help anyway

Thanks, folks! I'll study up some more and see what I can do with these things. On the plus side, I want to say that my current hub only transmits at 10MBps, so this would be a step up I assume. It sure was nice to get these handed to me. I looked on ebay and they're going for quite a bit. The one positive aspect of working here is that since nobody knows what all these old computer parts do, it's easy to nab them when the tech support guys tell them to upgrade I've gotten a bunch of stuff from here.

Thanks again!!

OKay, my switch has been installed. I can't really test to see if speed has improved, because I currently have one computer on the network (the rest were taken home by roommates for the summer). But it was a simple task to remove the hub and simply put the switch in its place. I was right that the hub was only 10base-T, so that probably explains why it took forever for my roomate to transfer files to my computer.

Anyway, the reason I'm posting is because even though the unit is running, it sounds like there's a jet engine in my closet. I can't believe how loud it is! I've never had a desktop cumputer run this loudly. Does anyone have any suggestions on how I can quiet this thing down? I'm going to open the second one up in a few moments (I only put one in because I only have about 8 lines in my house, so 24 ports were enough ).

Oh. Good point. They are loud. They were intended for wiring closets, not residential applications. I don't know of anything you could do to quiet it, other than replacing or removing the fan(s), and I don't know the potential downside of that.

I used an older 3Com hub (same size) earlier, also 24 ports, and I had no problems after I took off the lid and disconnected the fan. I left it running without the lid though. It only got slightly warm.

Stig

And it's all solid-state, too, so heat shouldn't affect it as much as if there were a hard drive in there. Still, replacing the fan with a quieter one would probably be better.

This is true. Plus, I assume that with 7 or 8 ports connected (and only 3 or 4 with packets being sent on them), I can't imagine there would be much stress on it.

Unfortunately, I can't imagine how to get the cover off! There aren't any screws on the back, and the ones on the bottom don't seem to be connected through the case, but they might be. I'm able to remove a back plate, and see inside, but I can't see what's what.

You might be better off eBaying them and using a tiny porportion of the profits to buy a regular 8-port switch (you can pick one up for about $25).

I was in the market for a 10/100 switch for my home LAN recently, and I deliberately checked to make sure that it was a fan-less model before I placed the order. I know how loud some of those industrial switches can be, I've got a server room full of them. (I ended up buying a 16-port Linksys unit, EZXS16W.)

Yeah, free stuff can suck I tried plugging both in at the same time, and the total of 4 fans could be heard from 30 feet away and around a corner. It was a good thing I don't need 48 ports

David, that would be a good idea, but I think I'd kinda like to hang on to them for now. They're good switches, and if I ever need something like this in the future, I've got it.

I suppose if I can't get the thing open to work on it, it will be okay. The switch resides in a closet in my bathroom, and with that door and another door closed, I can't hear it at all.

I suppose I could also permanently stick something in the side to jam one of the fans

Yes, keep them as a learning experience. If you want to go into IS/IT, understanding the capabilities of a managed switch is a Good Thing. My last project was fixing out managed switch database which controlls basicaly all the security on the network. We can pull up a port on the hub, see what room it's in, what the last MAC address was on the port, who has that MAC registered, what IP they're assigned, and so on. We can also shut down ports, make it so anyone can use the ports, or make it so just registered computers can use the ports. They really are invaluble in any situation that requires any kind of security. Start learning about SNMP and the like, and start messing with the people you live with.

Matthew

I think that on the one I opened, the screws for the lid was on the bottom of the case.

About eBay-ing them, why not sell one of them and buy an 8- or 16-port switch and keep the other?

Stig

Okay, after a hell of a lot of prying, I've finally gotten the cover off the damn thing. I assume if was designed for ease of construction, and they assumed a business wouldn't want to void their warranty by screwing around with it, because I had to do a lot to get it off. At one point I had 4 screwdrivers jammed into the edge between the metal and the plastic cover, so the little plastic tabs would stay lifted out of their slots. Grr.

Anyway, now that it's off, I can see the pretty large fans that were making all the noise. A quick power up starts the jets going again (these fans aren't just loud, they have a noisy high frequency to them). So I powered down and started looking. It appears they are connected to the board of the PSU with those connectors (I don't know what they're called) that I have on my motherboard for plugging in various devices (PCU fan, PSU fan monitor, etc). Is it feasible to just rewire them to some quieter fans?

The main problem is with the screws holding the fans to the case. They look pretty permanent to me.

So here's the idea: the switch (I'll only be using one at a time), will be in a closed linen closet with only the edges around the door for ventilation. However, it will be on its own 6 cubic feet (approx.) of space. I'd then leave the cover off. Does this sound okay?

*edit*
and by the way, I hate torx screws.

I dunno if disabling those fans is a good idea. It looks to me like their primary purpose is to cool the PSU.

You can get away with a fan-less hub if the PSU is external, like the wall-wart unit that comes with my Linksys switch. But if you have a built-in PSU like that, I think you're taking a risk if you don't cool it.

Just my theory. I could be wrong. The question is... do you feel lucky?

The question is... do you feel lucky?

That's why I have two

So you think that even with the cover off, I should have it going? How about if I got quiet fans that I mounted somewhere around it with the case open? Could they be wired to those connectors the current fans have?

Cover off + quieter fan might be OK, assuming it's in a reasonably well-ventilated space.

You're welcome to just try it with no fan for a while and see if it gets too hot or not.

Hmm. Are those screws or rivets?

You could remove the PSU and drill/grind them out. Just be careful around the capacitors, and don't put it down on anything conductive.

One _very_ good reason _not_ to run with the cover off is to prevent somebody from reaching in the closet and electrocuting themselves. It would also increase the risk of something getting into it (like fleece lint) and getting ignited somehow.

I really would be tempted to get different fans for it and see what the effect is. Those switches were built for heavy duty use - I bet that if you looked at the specs that they would be quite happy at elevated ambient temperatures, and that is the reason for the loud fans. (Ever been in a server room when the AC fails?!) I'd bet that they'd run quite happily with quiet fans.

Questions; What is the power rating on the back of the switch? What is the rating of the fans?

Our blue-haired friend makes good points.