Jeff Liebermann wrote:
> On Fri, 09 Sep 2005 23:29:52 GMT, "DanR" <dhr22@sorrynospm.com> wrote:
>
>> Question about typical company network.
>
> Is "typical" a good reason not to itemize any of the hardware or
> operating systems involved?
>
>> We are looking at going gigabit mainly
>> because of a perceived network slowdown in the past 6 months or so.
>
> Gigabit is great for taking the load off servers. For example, if
> someone is doing regular backups or huge file transfers, running that
> traffic through a single 100baseTX port on a server will cause traffic
> constipation at the server. You would probably be better off
> installing a 2nd ethernet card in the server, but gigabit will help.
>
> However, once the traffic hits the ethernet switch, the only place it
> goes is to the destination machine. Other users, using other ports,
> such as to/from your T1 internet connection, will not be affected by
> the heavy traffic in the slightest. Therefore, based on your limited
> description of the topology, I doubt that gigabit is going to do
> anything useful.
>
>> But... some
>> of use are not sure that the 100 Mb T1 current network is really the fault.
>
> A T1 (DS1) is 1.544Mbits/sec. You'll get about 1.3Mbits/sec thruput
> in both directions. Have you benchmarked this connection? I suggest:
> http://nitro.ucsc.edu
> which may disclose some setup and buffer issues. The CSU/DSU for the
> T1 probably has a 10/100Mbit/sec ethernet port. No sense in making
> that gigabit as you only have 1.5Mbits/sec to move through it. The T1
> speed is the limiting factor.
>
> Please note that a T1 is no better than a common DSL connection except
> that it has far superior outgoing bandwidth. A 3 or 6Mbit/sec DSL
> line, or 6Mbit/sec cable modem, will outperform a T1 for incoming
> connections. If the T1 is clogged with junk, then perhaps some QoS
> will suffice to delay a bandwidth upgrade.
>
>> Question is: We have some really speedy computers on the network and some
>> not so speedy. Can slow clock speed computers drag down the entire network?
>
> With switches instead of hubs on a wired network, generally no. I can
> create some kind of science fiction situation where a slow machine
> will cause problems, but the ability of the switch to isolate traffic
> generally prevents interaction. However, if there is a common
> bottleneck for all the machines, such as the T1, then there will
> certainly be problems.
>
>> We have B /
>> G Wi-Fi on both sides of the firewall. Can they drag down overall speed of
>> the network?
>
> Generally no, but it's possible. What wireless does is create common
> network (air) path for all the wireless users. You no longer have the
> benefits of separate switched paths as in a wired ethernet switch.
> Only one radio may transmit in a given air space. The result is
> consider mutual interaction and interference among wireless users.
>
>> We have hubs / switches that feed other hubs / switches. How bad a
>> practice is that?
>
> It sucks. See the 5-4-3 rule for hubs.
> http://fcit.usf.edu/network/chap5/chap5.htm
> Note that a hub is a repeater and that many texts use the terms
> interchangeably. Basically, it says not to put more than 3 hubs in
> series. I've had so much trouble with spaghetti LAN's using hubs that
> I replace them with switches as soon as I find them. That includes
> 10/100 hubs which are actually worse than single speed hubs.
>
> Ideal is a central stackable and SNMP managed switch in a star
> topology. That never happens as "workgroups" tend to add switches
> where clusters of ethernet devices come together. As long as they use
> switches, I don't have much of a problem. I make sure that the
> collision domains do not become excessive and track the end to end
> wire lengths. Dig out your drafting pad or Visio network topology
> scribbler, and make a drawing of your network. It's impossible to
> troubleshoot network constipation problems without a road map.
>
>> There are about 50 wired drops around the building and around 8 wi-fi hot
>> spots.
>
> That's not a huge system. However, there are plenty of places where
> things can break.
>
>> Previous IT guy set the wi-fi up with all different SSIDs. We don't care
>> about lap top roaming so maybe that's not a big deal. Or not?
>
> Leave it alone. The only thing a common SSID gives you is the ability
> to roam around. Having different SSID's gives the user the ability to
> chose which access point they want to use. Using a common SSID leaves
> it to the flaky driver software, which never seems to get it right.
>
>> Any suggestions?
>
> Nope. Do you expect a mechanic to fix your car without telling him
> the make and model? Do you go to a doctor and not expound on where it
> hurts or how much? So, you get only general advice and sympathy.
>
> 1. Get some bandwidth and traffic monitoring going. Your CSU/DSU and
> router probably support SNMP. I suggest MRTG or RRDTool.
> http://www.mrtg.org
> http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/
> You can easily tell if your T1 is constipated. If so, then optimize,
> add QoS, or add more bandwidth. You may have bottlenecks or high
> error rates elsewhere.
>
> 2. Replace the hubs and dual speed hubs with switches. Don't bother
> with gigabit unless you're bottlenecked at the server(s).
>
> 3. Do some sniffing and see what *TYPE* of traffic is causing
> problems. I suggest Ethereal:
> http://www.ethereal.com
> This is tricky with a switch so be prepared to do some hardware
> juggling or managed switch configuration for a monitor port. Be
> prepared to "discover" virus, worm, and streaming traffic. One
> Bittorrent filesharing user will bring your network to a stop.
>
> 4. Draw a network map so you can ask for help. This is not a trivial
> exercise. It usually takes me about a week to do properly on a large
> and complex systems. Just finding all the devices, servers, and
> bootleg attachments are a major challenge. That includes noting MAC
> and IP addresses for identification.
>
> 5. Get help from someone experienced in network analysis and
> troubleshooting.

Yes, I should have provided more information about our network hardware. Problem
is I don't really know. We are a production company with 6 Avid sweets, 2 audio
sweets, one online editing room and an interactive department. We don't have any
IT people per se... but have designated one of our coders to be responsible for
the network. He's a sharp guy and seems to know his network jargon. And he is
new on the job having taken over the network from someone who left. Because I'm
fairly handy with computers in general I'm helping the boss think through our
move to giga-bit and the coincidental network / Internet slowdown we have been
experiencing. The main reason to go giga-bit is to move very large files around
on the network. (video files in the giga-Bytes) And because of the Internet
slowdown of late we are talking and wondering if that will improve Internet
throughput. Obviously it will be a fairly expensive endeavor to run all new
cable throughout the building and get new NICs. So we're also thinking about
only doing new giga-drops at some work stations and not the entire network. All
new drops will be home runs and if we do the entire building that means all home
runs. But there's a but and that is that we are considering fiber to the upper
floor because of long runs.
So that is a bit of background and I'm just trying to learn what I can so I can
ask intelligent questions and better understand what the heck is going on. I'm
basically a home network guy and that is the extent of my network hardware
knowledge.
I appreciate the help so far provided. Thank you all.
Jeff... when you say "A T1 (DS1) is 1.544Mbits/sec. You'll get about
1.3Mbits/sec thruput in both directions." Does that mean that just one
workstation at a time will see that throughput? If 10 computers / workstations
are at the same time doing a Microsoft update for example... are they sharing
that 1.3Mbit bandwidth? Are they each then downloading at 130Kb. Does it work
that way? Also curious about one of our people who constantly listens to
Internet radio streams. Any harm there?