Infrastructure Design

[jimpiccillo]

Working with a client to develop an upgraded networking infrastructure design. They have concerns regarding the network configuration proposed. They are going to have a Cisco 4507 core switch with either Cisco 3550 or 2950G closet switches.

The issue in the design is whether to daisy chain the closet switches or to run fiber back to the core for each of the closet switches?

The other issue is that we're trying to provide 1000mb to all of the closets and the client has concerns with the 2950g vs 3550 switches. We proposed the 2950G to reduce the cost.

Network has 400 nodes, consists of 5 closets, and requires room for expansion of 50 devices.

Any advise or preferences?

[lgijssel]

400 user in 5 closets means 80 users / closet on average.

When 80 users share 1Gig that is 1000/80 = 12,5 Mb per user.

I suppose that this will not be sufficient. So this is a point to consider a separate uplink for each switch or at least to have multiple uplinks per closet.

The 3550 is very expensive indeed as workgroup-switch. I think it will not pay off in an environment where there is a layer3 switch already. Therefore, I would opt for the 2950G.

Hope this helps you on your way a bit

Leo

[follisj]

First you need to look at how many users will be utilizing each closet. An evenly distributed user base will put 80 users per closet. This can be quite costly as you will need to solution at least 2 - 2950/3550-48s to accomodate each closet with little room to expand. Another consideration you may wish to pursue is putting in 4506s w/ 3 - 48 port 10/100 cards in each closet (including the supervisor in each will leave you with two empty slots per chassis). I do not notice anywhere a router in all this. This will give you the ability to guarantee expandability. I would definately keep the 4507 as the core switch. Do not daisy chain your switches. Each one should have a dedicated fiber strand back to the 4507 in which you should have a 6 port GBIC module to support all the buildings gigabit requirements. Not I do not mention the GBICS or the type of fiber as those will depend on the physical location of the comm closets. This is a very robust network design for only 400 nodes, but if they are running a lot of bandwidth intensive applications, then it is well worth the investment now.

[pmshah]

Hi,

The biggest question is about "right-sizing" the network. Some of the math given by others assumes constant utilization by users. In reality, you will most probably find that not even 2% of the 100Mbps bandwidth is utilized -- this includes the broadcasts.

Here is the question: What do the users do? Do they do any data-intensive tasks (like CAD/CAM) or do they just want to share files and browse the internet?

If they just want to share files, browse the internet or something similar, a 4507 with daisy-chained (in a loop) closet switches will work. Remember, the gigabit connection is actually going to be 2gigabits (ful-duplex). In most cases 2950G will work wonders. The backplane of a 2950g is fully-nonblocking with total switching-fabric backplane of 13.6 Gbps. So if all the ports were working 100% of the time (200Mbps*48 + 2gbps* 2), it would reach 13.6Gbps.

Even at that rate, the 2950g-48 with Enhanced Image will cut the muster.

But what is the best design? Basically dedicate 2 gig ports on 4507 for each closet. One for regular use and one for backup. Connect the first Gig port to the top switch, the second gig port to the bottom switch and connect both the closet switches to each other.

So where do you use 3550? You should use 3550 where you need end-to-end routing (I have not come across that senario yet). In the 3550, each port is a routable port. In most cases 3550 is an overkill.

If you need any further clarifications, you can contact me at pritish @ yahoo.com

Regards,

Pritish

[bs6825]

We have a building very similar to this. My suggestion is to run fiber to each switch. You will need a couple 6 port gig blades for the 4507 which makes this a pricier solution, but consider the follwing:

1. If daisy chained, a failure of the "top" closet switch impacts all daisy chained switches.

2. The bandwidth will be much greater.

3. You can cross-link the closet switches forming a loop, so in case of a line or GBIC failure no one loses connectivity. (A GBIC failure is the most likey failure in this setup).

As far as the 2950 v 3550 goes, that is pretty much up to you. We have standardized on the 3550 due to its flexibility and scalability.

Hope this helps. Any questions? bs6825@cableaz.com

[scottchen]

I would definitely not daisy chain the closet due to the fact that in the event that a switch in the daisy chain fails, all switches after that would also fail. Daisy chaining will give you less bandwidth going back to the 4507. I would run fiber and connect the switches from each close back to the 4507 via 1GB fiber. This not only gives you the bandwidth capacity but also gives you a design where each IDF does not depend on another IDF to obtain connectivity. As for the 2950 vs 3550. It appears that in your scenario the 2950 would make enough sense. The 3550 is fairly expensive as far as I know. Assuming that your 4507 has a L3 module or hooked up to one, I would separate each closet into a separate network. Though it appears that 400/5 = 80 users per IDF may sound like it's an over kill, this provides you the ability to not only grow but also gives you ease of manageability and troubleshooting easability. Hope this helps.

[kenjohnson]

The 3550 is really not that bad as long as you don't put the layer 3 option on it. As a layer 2 switch (workgroup switch under a 4507R for example) -it's as affordable as most other catalyst swithces...

- Ken