Design Question...

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Nov 19th, 2007
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We have a proposed design as you see it in the attached diagram. We want to use GLBP between the two 6500's and each of them are in a separate physical site that is connected via single mode fiber. As you can see we have connected the 4948's, which are acting as Layer 2 distribution switches, using the fiber. The 6500's are each part of the GLBP setup.

Is this a bad way to set this up? What I am looking for is drawbacks or alternative setups using the same equipment.


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william.briere Mon, 11/19/2007 - 08:57
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Thanks for the response...

Can someone comment on whether or not there is a technical reason why the setup as it is presented in this diagram will not work?

Tony.henry Mon, 11/19/2007 - 18:44
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No reason it shouldn't work... that said, I wouldn't want to install it this way either.

I'd like to see the two core switches joined together so that they aren't using the distribution switches as trasit devices.

I would also look to dual home the distribution switches to the cores. I've attached a dodgy drawing of what I would do.

Spanning tree is bit of a issue in my network where in yours it's not so much rapid spanning tree will sort that out easily. I guess it's dependent on what your building the network for. Are the core switches where the servers are? That would be an issue in your network as the Core switches will get isolated should you lose one of your distribution switches. where it's not a problem in mine.

any way have a look and shoot holes in it if needed. every design has flaws. I might just need to understand your requirements a bit better...


william.briere Tue, 11/20/2007 - 05:37
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This configuration was chosen because the connection between the two sites is via fiber. I had to use the 4948's as the connection between the two sites because on the 6500's I don't have a fiber card, Only the two ports on the sup 720's. (So no place to terminate)

Is it bad that I have connected things via the 4948's? I thought it would minimize the chances of failure by adding more connections between the sites. I plan to add two more 4948's to the site "a" which would make 4 fiber connections between the sites. On one side there would be 4 fiber cables, one on each 4948, going directly into the two 4948's in site "b" (As you know there are 4 sfp ports on a 4948).

Is there a better way to do it given my apparent limitation?

I really appreciate the insight of whomever answers!

william.briere Tue, 11/20/2007 - 11:01
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Hello Netpros,

I am really anxious to hear the comments from the experts here...

Please respond :)

mohindersingh Tue, 11/20/2007 - 12:03
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Hi William,

In a good topology, core should be connected with each other.

As you said you don,t have fibre ports on 6500, i don,t think you are having any other choice.

So i think the only left solution is connecting the sites through 4948 swicthes with fibre.

i don,t think connecting two more switches in each sites will not give any benefit.

As sfp will block all redundant ports.

may be if you want you can create etherchannel on each 4948(2).



Tony.henry Tue, 11/20/2007 - 12:53
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As I said, I'd like to see the Cores switches connected directly together.

That said, what requirements have you got on how this network fits together? you need to answer for yourself,

What is connecting to the core switches?

What is the availability requirement for these devices?

Where is the gateway, for the site and what reliability does that need?

I'd be hesitant to say that the design as you have it is bad. I couldn't say it's good either. There is simply more to the equation than a diagram showing switch connectivity.



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