Hubs and Switch stuff 3

[pikk]

Hi,

Looking for a pro to give me some advice and tips on re-configuring my network. I'll try and provide as much info as possible.

Currently, I am sys admin for a 55 node (client) network running an NT4 PDC, BDC and Exchange 5.5 server. (most systems running 3Com NICs) Various other servers exist but are not as relevant. My big problem is collisions (they get so bad at times that they halt the server traffic completely) and I suspect it is the hubs and the way everything is configured. I took over from a previous sysadmin and needless to say...everything is a mess. What we have are 5 Intel Hubs (not switches) interconnected to one another through an RJ45 port on the front. Two are actually cascaded. My thinking is that this is the main problem. Also in use are various (3) other small 3com hubs to extend the network. Ever since installing a Linux box to server as a gateway for internet, mail etc., I have noticed a lot of duplex errors on the screen. I suspect as well that this is a result of the poor wiring and hub configuration. What I need to know is would swapping out 2-3 hubs for good quality switches provide a resolution? We are going to be expanding the network by about 10 users soon and I have to figure out how to upgrade and stabilize things first. Any help would be more than appreciated.

I thank you in advance,

Pikk

 

[jimbopalmer]

You can do MUCH better with switches over Hubs. Hubs are half duplex they only send or receive, switches can do full duplex where they send and receive. in general a large Switch ( or cascaded switches) will do better than many smaller switches, but distance will make some of those choices.

I use Nortel Baystack 450s, but I need remote administration, you can use cheaper unmanaged switches if you have just one site. the 450s hold 24 ports and can be cascaded 8 high for 192 ports of 10/100, you might only need 3.

be carefull to get duplex right, Full is faster than half, but a mix of full at one end and half at the other is very slow, most new equipment auto dectes very nicely.

I would convert by setting the switch to 10/half and moving the wires, then 'upgrade' each port one at a time to find how good it really is.

good hunting on ebay! I tried to remain child-like, all I acheived was childish.

 

[pikk]

Thanks for the info Jim!

I kind of suspected that. The hubs were fine when we were only 10 people. I will certainly start pricing out some new switches.

Pikk

 

[MasterRacker]

When you're cascading switches, make sure you're doing it with 1GB fiber or, better yet, the 2.5 GB backplane cascade cables (assuming you're using 450's).

If you chain switches using crossover cables, all the subsequent switches are still only sharing the bandwidth of a single port on th "master" switch. The reason I bring this up is that's probably exactly what you have with a organically grown hub based network. ("... just plug in another hub and we'll have more ports....&quot Happens all the time, when it's not a "designed" network. Using a topology that creates some kind of high speed backbone between the switches will give a lot better performance.

I buy my 450's from here

http://www.cxtec.com/.

They have a lot of equipment available on a program they call "equal2new". Essentially is refurbished stuff with a 3 year warranty but a BIG price savings.
Jeff
I haven't lost my mind - I know it's backed up on tape somewhere ....

 

[pikk]

Jeff,

Thanks for the reply. I take it that is a US company? We're in Canada and well, you now how our dollar's doin right now

Anyway, another quick question...would I be safe to dump a couple of the old hubs and buy a couple of switches? Would this be an imporvement over my existing setup. I guess it all hinges on a fairly tight budget is why I ask.

Thnx again.
Pikk

 

[Jsteve]

Pikk,

Wow, sounds like your in broadcast hell, lol ;0)

A couple of switches will help somewhat. It depends on
how your going to config them. are you going to config vlans or are you planning to use the switches in the same manner as your hubs?

depending on your budget, I would say buy one high end L2/L3
switch and one low end, in that way you can continue to scale your network without losing performance.


I would recomend a Cat5000 with a RSM and a NFFC for the high end.

and a Cat1900 for the low end.

 

[pikk]

Jsteve

Yes! Broadcast hell is right and maybe an understatement. Gotta do something. We're planning on another 7-10 employees and I've got to make some changes. My thought was to buy 2 high end switches and then split up the network somewhat. By this I mean I was thinking of putting 2 hubs with each new switch and connecting the switches directly to the server side. Does this make sense? I'm a little new to the physical (hubs,switches,routers etc.) We have two separate physical areas of our network that I could split up if I have to. Segment I think is the word. I could run two dhcp servers for this I suspect...now I'm just rambling...what are your thoughts?

Thanks tons!!

P'

 

[Jsteve]

If you have that kind of budget, the best set up for is a mini campus design. The access and distribution layers minus the core.

I would get one Cat5000 with RSM(ROuter Switch Module) card and a NFFC(net flow feature card) for the distribution layer.

and Three Cat1924(total 72 ethernet ports and 6 fastethernet ports) for the access layer and get rid of the hubs.

Connect the three Cat1924(through the fastethernet ports) to the Cat5000 and ALL of the nodes and servers, connect to the three Cat1924. you don't want to connect any nodes to the Cat5000 because it will simulate a Core/distribution switch.

The key is the router card with the L2/L3 switch so that
you can configure inter Vlan communication to limit your broadcast and provide the best security control. Buying two high end switches and adding hubs is not a good scalable design. also with the hubs you will still have one large collision domain with each hub, while the switches eliminates the collision domains.

 

[Jsteve]

Also you can connect both of the fastethernet ports of each cat1900 to the cat5000 and configure EtherChannel for the trunk ports to load balance. That way , you will never have to worry about bandwidth in your backbone.

The only other thing is your unix server, because it provides Internet access to your company, I would consider putting it at the Distribution layer, attached to the Cat5000.

 

[jimbopalmer]

A nortel/ebay solution is

1) One Accelar 1100 a 16 10/100 port routing switch, with two slots for expansion. I see these around $250 USD

http://cq-search.ebay.com/search/se...Property=MetaEndSort&ht=1&query=accelar+1100*

2) Two Baystack 450-24T a 24 port 10/100 Switch (you may use Multilink trunking to attach them to the 1100 at 400 Mbps full duplex, or buy gigabit cards for the 450s and 1100) I see these around $400 on ebay

http://cq-search.ebay.com/search/se...&st=2&SortProperty=MetaEndSort&BasicSearch=++

That would net you 48 ports, which sounds like your need in the central area. Cheap 8 port switches in the remote location may well be $40 each (shipping will drive all these prices up) link them to the 1100 as well.

http://search-desc.ebay.com/search/...ery=8-Port+10/100+Ethernet+Switch+&srchdesc=y

And I bet, with higher speeds/better diagnostics some cables will need replaced. I tried to remain child-like, all I acheived was childish.

 

[wybnormal]

A 5000?? Multilayer switching? I dont think so.. there is not anything said so far to justify such an outlay. Cisco's own best practices do not suggest a 5000 until you get around 250-300 port density and then, no RSM. The RSM is needed only where you decide to hang vlans off things. But even then, a cheaper 2620 can be a router on a stick just fine. If you are willing to get USED equipment(read as refurbished) you can save a ton of money. I would not recommend an "off brand" unless you have expertise with it because odds are high that not many others will have it either.

You are talking under 100 nodes? take a hard look at either used 2924( roughly 800$ US each) and stack them. Feed the switches in on 100 Full duplex links.. most of your users will be fine at 10 1/2 unless you have a bunch of powerusers like SQL developers etc.

You could shop around and get a used Cat5K with the 10 1/2 cards already included for something from 1500 to 2500 US$.

Before you start worrying about broadcasts, get a baseline sniff of the network. Why? because I have run 3 large networks ( over 2K nodes each) that were FLAT at the start and they worked. Not the best to be sure but they did work. So it would take ALOT of broadcast traffic on 100 nodes to kill your network. You gotta keep things in perspective. Just because you can do VLANs doesnt mean it's the best or cost effective solution.

I think you are on the right track worrying about collisions.. hubs are bad for this and everybody sees everybody elses packet.. broadcast or not. Switches on the other hand will break up the collision domain into smaller units which increase *apparent* bandwidth. Routers break up broadcast domains and now you will need to come up with a IP scheme, VLAN design, gettings WINS/PDC authentication, DNS, BOOTP(DHCP) and etc across the subnet boundries. It can be done but it's a bit of work.

You dont need two DHCP servers.. you would need to enable UDP forwarding or IP Helper if it's cisco based. Or you have the router itself hand out the IPs..

MikeS
Find me at

http://www.packetattack.com

"The trouble with giving up civil rights is that you never get them back"

 

[pikk]

Phew! Thanks Mike...I needed that.

Just what I was lookin for.

Pikk

 

[patrckb]

pikk,

I'm wondering with all your interconnected hubs if you might be experiencing the effects of a 5-4-3 rule violation (re:

http://www.micronet-america.com/techinfo/note/5-4-3.pdf).

This could cause late collisions that would really slow down your network. Again, the solution is a core of switches.