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Big project: comments?

jon-o asked
Medium Priority
Last Modified: 2010-03-17
My university has ethernet connections in its residences for internet. Right now my computer is connected to it via an accton ethernet card. My great plan is to get another computer (CHEAP!!!) and have it plugged into the university connection, then connect my computer, and up to 2 more computers at the same time. The new computer would run linux and various servers (ftp, www, mail) and presumably route the stuff between the other computers. My bit question is, is this a good way to go about this? The only comment I've gotten form anyone so far is that I should use a hub - can anyone tell me the pros and cons of this method? Thanks!
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Well, a hub is basically just an appliance to get multiple 10BaseT jacks out of one.  You'll need one of those anyway if you want 10BaseT ethernet to all your computers; all you do is plug the hub into the wall and into your computers and you have multiple Ethernet adapters on the network.

After that, what you do depends largely on what your university will do for you.  If they will give you an IP address for each of those Ethernet adapters (NICs), then you basically have no need to configure your Linux as an IP router of any kind.  All the computers can be directly connected to the internet.  If, on the other hand, it's one IP address per NIC, you'll want to run your Linux as a "masquerading router".  This is what I do at home.  The only difference is that you will be ethernet only and I am ethernet and PPP, but the idea is the same.  Basically you configure your linux box to have two different IP addresses, you can do this by IP aliasing on your Linux's single NIC.  You can have your Linux box on the valid IP for Internet, then on for your LAN.  The rest of your computers can be,, ... and can use as their internet gateway.  This is called reserved Class 10 addressing.  The network is a Class A address reserved for local area network routing.  Your Linux box can act as a masquerading router between network and whatever your school's IP network address is.  To the outside, it just looks like all the traffic is coming from your one valid IP address.  To the inside, your LAN, your computers just think they're directly connected to the internet on a Class A network.  But this is a complex topic, fun, but complex; if youre interested in this kind of setup, read the docs and then get back to me with any questions.

If you want to get away without using a hub, you can do that too.  Maybe you could have a 10BaseT and a Coax NIC (2 NICs) in your linux box, plug the 10BaseT adapter into the wall, then run coax to the rest of your computers.  In that case however you would certainly have to use your linux as a router, and believe it or not, masquerading would be easier under that setup than real addresses, just because if you use real addresses you would have to get the school to give you a "subnet", something they probably wouldnt be too keen on doing, since they lose IP addresses that way.  In the case where your linux box has 2 NICs, the coax network would be the one that runs network address, the only difference is that instead of aliasing, you now have two IP addresses for two NICs and your Linux routes between them using masquerading.

This last option is probably what I would go for in your shoes, since even the cheapest hub costs around USD $100, and you can buy used coax (10Base2) ethernet adapters for like $15 a piece if you look around.  With all 10BaseT and a hub, it's simpler to get it working but its also more expensive.  Plus, if you get the 10BaseT<->10Base2 IP masquerading Linux router thing set up, then you can brag to your friends about your dorm room's LAN, and have girls up to your room to play net games over the internet :)

Oh the other good thing about running to coax on your dorm room's LAN is that you never run out of jacks, you can just extend the loop.  Lotsa people think coax is bad just cos it's cheap and it's real easy to break the cabling, but i think for LANs in your house and stuff like that you cant beat it for price/flexibility.

Well that's my $0.02, mail me directly if you have any questions or comments or whatever.  Good luck!


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