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School ADSL down! Wither the Internet...

By pr0teus ·
OK, "TechRepundits", here's one from the annals of networking ****.

My company was called in by a High School to resolve Internet access issues they had been having partly due to (and since) Hurricane Ivan "The Terrible".

Ivan took out several of their lines, including the line used for their ADSL access. ADSL connection: 768 kbps (down)/ 256 kbps (up). The telephone lines were reconnected, but since then the service had been considerably poor (in their words). When we were called in the line had previously been disrupted again, and service had just been restored. The "technicians" at the school had NO idea as to how to configure the modem. The original config had the modem connecting to a single machine on the network (Network uses CNSH1600 switches, unit to which modem was attached had two NIC's) We did a reconfiguration, ran a connection directly from one of the switches to the modem, and had everyone getting access (though service left a little to be desired, wasn't too great, wasn't "terribly poor"). This was done on a Saturday, by Monday morning NOBODY had a connection!!!! The DSL line kept "dropping out" - you would literally see the line sync light disappear then come back after a few minutes.

However, I have yet to explain the physical infrastructure of the school's networks (that's right plural networkSSSS).
___ ~30 Yds | |~20 Yds _______
| |---------| |--------| |
|___| |____________| |_______|
Admin Library/Comp. Lab2 Comp. Lab1

OOOOOOPS! That was awful!!!

_____~~30 Yds |____________|~20 Yds _______
Admin______Library/Comp. Lab2_______Comp. Lab1

Hope this quasi-diagram does some justice. In all we have more than 150 computers feeding from the DSL connection. Admin has 16 machines, Library ~72, and Comp Lab1 ~70. Additionally, there is a standalone computer used by a teacher that is also connected. The networks are interlinked by cat5 cables running from their respective switches into the switch in the Library. Each network has a server (windows 2000 server in each case).

Now, when the adsl connection is setup on a standalone machine it blazes!!! Rip-roaring speed!! Drop it back onto the switch and everything goes south! Slow or non-existent service.

We also found that at times (though not consistently so) removing, say, ADMIN or all external networks would improve the quality of service in the Library (where the ADSL connection is physically located, BTW), but the improvement was never one of great speed, more akin to a fast dialup. Also if we took the ADMIN interlink cable out of the Library switch (essentially isolating ADMIN) and plugged it directly into the modem, (i.e. ADMIN ONLY connected to the modem) the service was still poor to non-existent, and very inconsistent.

Library server is running Symantec NAV Corp ED, protecting all machines connected to Library network, we did a random check on several machines found little or no spyware/malware. ADMIN machines were infested with viruses (OK, maybe I exaggerate - but just a little), almost every unit had at least one virus, and an average of ~20 spyware/adware threats (some were a great deal more). We cleaned the machines of all threats - virus/spyware - checked connection speed with only ADMIN connected to the modem and....SHAZZAM!.... still poor connection speeds.

What say you great minds of TechRepublic???!!!

i) Networks are using 192.168.etc. IP range
ii) Modem was by default, but changed to to work on the network
iii) All servers run their own DHCP, using as router/gateway
iv) are reserved, DHCP's only hand out from 31 up

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Another attempt at diagram

by pr0teus In reply to School ADSL down! Wither ...

_____~~30 Yds |____________|~20 Yds _______
Admin______Library/Comp. Lab2_______Comp. Lab1

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by apotheon In reply to School ADSL down! Wither ...

All those computers are sharing one ADSL connection? No wonder there are issues. That's too little bandwidth for that many machines. This setup needs a T1 line. That is, in fact, exactly the sort of setup T1 was designed for.

You're likely to see ****-poor performance no matter what you do, as long as you have that many computers on the network.

Also, any time you've got parasite software on systems that are sharing bandwidth, a lot of that bandwidth is going to get eaten for lunch by the spyware and adware. That's a given. You need to solve that.

Get some network monitoring tools, like Netsaint and the like, to use for checking what traffic is going on with the network. That will help you narrow down specific problems. Unfortunately, considering that it sounds like everything is Windows-based, most of the good network monitoring software out there is Unix-based. If you have a Linux laptop, you should be able to get dozens of good utilities for free that will work better in the hands of a competent network security auditor than most commercial "professional" tools.

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T1 vs 3x768

by pr0teus In reply to bandwidth

That was a consideration, but answer these questions:

1. Why doesn't the service improve when we ONLY have ADMIN on the modem (16 computers should run wonderfully on a 768 connection)

2. Don't ask why, but getting 3 x 768 connections is cheaper than a T1 (~1.5 Mbps), wouldn't we be better off getting 3 separate connections for each lab?

3. Why was there no improvement in service when spyware was removed (once again, with ADMIN as the test network - all machines were scrubbed)

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good questions

by apotheon In reply to T1 vs 3x768

1. Obviously, there's something wrong with the admin network. Without being there, I can't really tell you what. See 3 below.

2. Probably, for now. T1 is more scalable than redundant DSL, though. It depends on how much the school's Internet needs are likely to expand in the forseeable future, and how much they want to plan ahead. Multiple DSL lines might be a good answer, though. In any case, one DSL connection isn't likely to cut it.

3. It's entirely possible you didn't get rid of every piece of malicious software.

Note: I haven't reread your original post(s). Please forgive the oversight if I'm misremembering something.

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Some Suggestions and more questions

by butt In reply to School ADSL down! Wither ...

You said that all servers run DHCP so does this mean that there are multiple DHCP scopes all running the same set of network addresses?

How do you have DNS setup forwarders setup properly?

Have you tried a proxy server? You can reduce your internet use a great deal by caching pages internet traffic by using a dedicated proxy server (It doesn't need to be much of a machine just a big HDD)

Send me your email address and I'll send you a proposal diagram Visio

I would be inclined to add a router somewhere (you can use win2000 if you want to) probably separating the 72 machine from the library out from the rest of the network.

make sure you are running dns or wins or both and in DHCP set wins type to hybrid

at the very least I would add some sort of NAT device to the adsl modem (unless it is built in)

I think you really need a caching server or more bandwidth but reducing broadcasts is a priority you will also need to either get everyone on one subnet or route the packets and use different network addresses
ie: admin =
LAb1 =
Library =
Then route the networks.

If you are using all the same networks then the nat device is getting confused. (I think)

Hope this helps

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by jhansen In reply to School ADSL down! Wither ...

make sure your not using conflicting subnets. for example...


192.168.0.x 192.168.0.x 192.168.0.x
(BAD, even if all on different DHCP SERVERS)

192.168.1.x 192.168.3.x 192.168.4.x

with out more info its hard to give you more info
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