Need help designing large-scale network

[carl4286]

Hello! I'm an undergraduate CS student at Purdue University, and through a series of events that I won't bother explaining, I recently inherited the responsibility of fixing a network that serves about 100 students through a combination of 28 ethernet ports and several wireless access points. The currently have the following equipment at hand:

Westell 6100 ADSL modem (connected to Verizon DSL)
Dynex 4-port 10/100 wired router (I did not choose this brand, trust me)
Cisco WS-C2948G 48-port switch
6 x Netgear WN802T-200 dual-band access points

This is how the network is currently configured... the ADSL modem is in bridge mode, and it is connected to the Dynex router. The Dynex has DHCP/NAT enabled, and it feeds into the Cisco switch. The switch then connects to the 28 ethernet cables + the 6 access points, and the access points are configured for uninterrupted roaming (this was all done when I arrived).

This all sounds nice, but for some reason everything completely falls apart when people start loading up the network. Even though wireless coverage is excellent, most of the wireless users end up with 169.254.x.x IP addresses (a sign that they aren't being assigned a proper one by the router) and no default gateway, and internet connectivity is intermittent at best, and nonexistent at worst. My only working theory is that the Dynex router isn't powerful enough to handle the number of users requesting IP addresses/connectivity. However, I replaced the Dynex with my personal Apple Airport Extreme, and it was unable to connect to the internet except for through the Dynex router (confusing, I know).

My question is, if you had all of the equipment above and maybe a few hundred dollars to through around (but certainly less than $500), how would you configure the network to allow everyone to access the internet uninterrupted? I realize that the connection will be slow, but that is out of my control. I just want to get everyone connected. Thank you so much for your help!

 

[seepy83]

Since you don't really have a budget for other equipment, I'd start by not spending any money and throwing a server (doesn't need to be anything fancy...any box that will run a Server OS) on the switch and letting it handle DHCP/DNS for the network. See if that eliminates your addressing problem.

Other than that...you're trying to serve 100 connections with a pile of crap. For that many users, the Wireless sounds like it is in desperate need of some enterprise-class equipment (APs with a central controller).

I might also setup some SPAN ports on the switch and load up Wireshark to take a look at what's happening on the wire.

 

[JohnG86]

Do you have a old PC (500 MHz and 512 MB of RAM is enough) laying around and 2 network cards? If possible setup Smoothwall, IPCop or any flavor of linux and set it up to replace the Dynex router. A PC as the router is more reliable then buying another cheap router that will have the same issues handing out lots of IP addresses.

Linux based OS that are setup specific for routing usually are controlled through a web based interface. The initial configuration to get through the setup is the only time a keyboard, mouse and monitor should be needed and can be unplugged once the web interface is working. I do not know if this option would also allow it to be a radius server for the APs.

 

[kevnich2]

For your type of network, you don't need anything super duper - 28 clients isn't really that much. You just need a good, reliable router. I'd go with just a SOHO router with a good amount of memory to be able to handle alot of connections. The Asus WL-500G Premium v2 should be able to do this pretty well for you and only costs like $60. You could get a more beefy router but considering your internet connection, you don't need anything else besides this. That Dynex router is just plain crap. The rest of your infrastructure (minus the DSL connection of course) is pretty adequate.

 

[seepy83]

Originally posted by: kevnich2
For your type of network, you don't need anything super duper - 28 clients isn't really that much. You just need a good, reliable router. I'd go with just a SOHO router with a good amount of memory to be able to handle alot of connections. The Asus WL-500G Premium v2 should be able to do this pretty well for you and only costs like $60. You could get a more beefy router but considering your internet connection, you don't need anything else besides this. That Dynex router is just plain crap. The rest of your infrastructure (minus the DSL connection of course) is pretty adequate.

He's serving 100 clients (including Wireless).

 

[Lean L]

get a cheap cisco off ebay

 

[netsysadmin]

I am guessing they setup the Dynex router to serve up the IP's via DHCP. Since you are having some clients getting the 169 addresses it is possible that you are out of leases on the Dynex unit. I would check to make sure they max number of leases is set a high as possible ans see if you are running out.

John

 

[seepy83]

Originally posted by: netsysadmin
I am guessing they setup the Dynex router to serve up the IP's via DHCP. Since you are having some clients getting the 169 addresses it is possible that you are out of leases on the Dynex unit. I would check to make sure they max number of leases is set a high as possible ans see if you are running out.

John

Also, you'll want to check settings for Lease Duration. You said you're serving about 100 connections...is this always the same 100 computers, or could it be any 100 from a pool of many more (i.e. "we have 1000 students, and 100 of them might be on this network at any given time")? You might have Leases sticking around from PCs that aren't connected at that particular time...

 

[RebateMonger]

Originally posted by: seepy83
Also, you'll want to check settings for Lease Duration.

Yeah, it's quite easy to run out of DHCP leases in a large network with many PCs checking in and out. Make sure that's not what's happening. If some clients are getting IPs and their networking is working fine, then the problem is likely a lack of available IP addresses.

 

[James Bond]

Originally posted by: iamanidiot
get a cheap cisco off ebay

Yep, this. Grab a 2650XM with full RAM/Flash and load 12.4 on it.

 

[James Bond]

Originally posted by: RebateMonger

Originally posted by: seepy83
Also, you'll want to check settings for Lease Duration.

Yeah, it's quite easy to run out of DHCP leases in a large network with many PCs checking in and out. Make sure that's not what's happening. If some clients are getting IPs and their networking is working fine, then the problem is likely a lack of available IP addresses.

Hadn't thought of this, but it's very likely that this is the problem.

If this is the problem, lower the lease time (it's probably set at something like a week..). You could lower it to something like 1 day.

 

[seepy83]

Originally posted by: James Bond
You could lower it to something like 1 day.

Or even lower than that, depending on the situation. I don't know what his pool of addresses looks like...but if this is at a college campus, I could easily see a different 50 people connecting to that wireless every hour. If he only has a Class C to work with, then even a 1 day lease might be a problem. 2-3 hours?

 

[spidey07]

I recommend a lease time of 1-4 hours for any machines that come in and out of the subnet. There is no downside or detriment to doing this.

-edit-
And say hi to my old dorm room at Wiley Hall and tell the sig epps I miss them.

 

[bruceb]

DSL is not exactly a high speed / capacity line. That in itself, will bottleneck the network. You should try to find a higher speed ISP service first and see what that does. Going from say 3MBS download to about 15MBS download should help.

 

[kevnich2]

Originally posted by: seepy83

Originally posted by: kevnich2
For your type of network, you don't need anything super duper - 28 clients isn't really that much. You just need a good, reliable router. I'd go with just a SOHO router with a good amount of memory to be able to handle alot of connections. The Asus WL-500G Premium v2 should be able to do this pretty well for you and only costs like $60. You could get a more beefy router but considering your internet connection, you don't need anything else besides this. That Dynex router is just plain crap. The rest of your infrastructure (minus the DSL connection of course) is pretty adequate.

He's serving 100 clients (including Wireless).

Yeah I was busy with other things at the time and mis-read some of what the OP said (obviously) and mis-took 28 ports for 28 clients. My mistake.

I'd definitely look at the lease time of the dynex and just lower it to maybe just a few hours or even just an hour and see if that helps. Although if you have 100 clients on a DSL connection, that right there will be one of your biggest bottlenecks. People would WISH they had dialup with those kinds of speeds. I know how college people are with the internet, I've seen some that spend 24/7 downloading torrents (that they never need but do just because??) If the dynex is reliable and doesn't need rebooting constantly, just look at the DHCP lease and see if it's just running out of IP's.

 

[carl4286]

Thanks guys!! I read everyone's comments, and tried pretty much everything that you all suggested, and the network is more-or-less 100% operational. Albeit, on mostly borrowed equipment. I listened to what you all said about the router running out of IP addresses, but I periodically checked the client list and it peaked at around 66 users. Also, the least time was set to 2 hours by default.

What I ended up doing was borrowing a small business router to replace the Dynex and a newer (and guaranteed working) 3COM 48-port gigabit switch to replace our Cisco. With this equipment, the network has been up for about 36 hours now. I guess the Dynex just isn't beefy enough to handle the number of users, and the switch (which was purchased in 2000) seems to have been malfunctioning.

I plan on shelling about $600 for a new switch and business class router, and hopefully that will solve the problem for good. Thanks!