Best Practices on LAN design and setup

Unanswered Question
Nov 6th, 2002

I am surveying to see what is the Best Practices on setting up a LAN for approx 350 devices including users - using only 2924s switches. For example in the past I have been using 2924 switches with crossovers between the other switches in the closet. In the past (still using it this way) for example I will take all of the crossovers from the stack and plug them into one switch. EX - port 1 will go to a router, port 2 will be crossover to switch 2, port 3 will be crossover to switch 3, port 5 will be crossover to switch 5, ect...... Now I am wanting to know if others out ther are doing the same thing or is everyone daisy chaining the switches together. Please let me know I would appreciate it. You can email me at Bolds@trammellcrow.com. Thanks for your input.

Thanks again, Brandon

I have this problem too.
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kgbsd Wed, 11/06/2002 - 17:43

Currently I run all of my 1900 switches and a router at each location intoa 2950 switch. Basically it acts as the backbone for that LAN and the router has instant access to the other switches instead of being 4 or 5 switches down the line..

jfraasch Thu, 11/07/2002 - 09:32

I think the solution to this problem depends on the physical layout of the location. If all 350 users are wired to the same closet then it makes a heck of a lot of sense for price and performance to go with a closet switch like the 4000 series. It will host 240 ethernet ports. And the cost will be close to the same as buying ten 2924's (probably cheaper).

Additionally, I don't think it is a good idea to daisy chain more than 3 switches together for any reason. If you daisy chain five 2924's together then you have 120 users all competing for 10mb (or 100mb) of bandwidth between the the final uplink switch and the router. That can severely impact the performance.

If you want to stick to the 2924 layout then I would get a single layer 3 switch and use it at the distribution layer. You could daisy chain two or three 2924's together and then plug them into a 3550-24 then daisy chain three more 2924's and plug them into another port of the 3550-24. Put each of those 2924 clusters in their own VLANs and you have yourself a smokin little network. With the 3550, only traffic destined for the router will be using the 10 or 100mb uplink to go to the internet.

Also, if you can ONLY use 2924's then you should get a router with at least two ethernet interfaces. Plug half your 2924's into one interface and half into the other to limit broadcast domains and maximize bandwidth.

James

wkumari Fri, 11/08/2002 - 07:35

One thing that immeditaly jumps out at me here is that all of your users are relying on the same (top) switch. What I would prefer to see Switches 1,3,5,.. going into one "top" switch and 2,4,6... going into a different "top" switch. If you are worried about wasting "top" switch ports, just plug some users directly into the "top" switches. The distribution switches then plug into different Ethernet ports on the router. This is assuming that you have users in different VLANs and so have to route between VLANs (and subnets!) anyway. If everyone is in the same L3 network, plaugging them into differnent ports on the same router is tricky (but dooable, see recent discuaaion on thisforum).

daveorenstein Thu, 11/14/2002 - 11:08

The configuration you describe appears to have a nice top down design, however it has two single points of failure.

The obvious one is the single "root" switch. The daisy chain design reduces the impact of switch failure, because you can quickly bypass the failed device to restore the majority of the network. The single "root" switch is also a potential bandwidth bottleneck. That would depend upon your traffic patterns. If you can afford to add a switch it would be a good idea to install a second

"root" switch in parallel and move half of your down stream switches to the new switch and link the two "roots" together. Leave a sufficient number of ports open on the "roots" to allow moving everything on to one switch if one or the other shoudl fail.

The second single point of failure is the single router. The question is what purpose does the router serve? Is it an access device or is your network seperated into Vlans?

Dave

spalislam Mon, 02/03/2003 - 08:19

I have very close network design layout. The way I did my switches is as follows:

6509 at the core.

GBIC interface connection to the 2950 as an uplink.

10 2950 connected to the main 2950 via 2-links EtherChannel at 200 Mbps/full duplex.

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Posted November 6, 2002 at 1:16 PM
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