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New Member

Switch Block Design

Hello... I'd like some feedback on a redundant network design that I worked up. It's a small/medium sized company so I went with a collapsed core using 3550-12G Switches. 3524 and 3548 switches would be used at the Access Layer and 2950-12 switches would be used for the Server and WAN blocks. Since the 3550's can handle Layer 3 routing, is it required to have a router at the Server and WAN blocks?

See this link:

Thanks for your input!


New Member

Re: Switch Block Design

Not sure what VLAN you were planning to make the backbone. Are the 3550's housed at one of the listed sites along the left? Are they near the servers?

One thing that occurs to me is that if the 3550's are in the same locale as the servers, then you might want to look at hanging the servers right off the 3550's.

Also, I'm not sure I would mix 2900 and 3500 series switches. They're in the same ballpark as far as price, and the 3500 has alot of advantages over the 2900s. Either go with all 2900s or all 3500s. It also seems wrong to put the slower 2900s at the server location, as this is where most of your traffic is going. If you connected the servers directly to the 3550s at the outset, you could start with 100TX and move straight into 1000T when you need a bigger pipe.

The final consideration regards spares. Try to stay with as few different device configurations as possible. This will make having a spare switch available for failures much easier.

It seems you could do this config with a mix of two or three devices, as follows:

-3550's in the core, 2950's everywhere else

-3550's in the core, 3524XLs everywhere else

-3550's in the core, mix of 3524XLs and 3548XLs everywhere else

-3550's in the core, 3550's in the server section, either 2950 or 3524/3548s everywhere else.

You're in good shape, just some product selections need to be looked at to make sure they really are the right devices.

New Member

Re: Switch Block Design

I'm not sure yet either which VLAN would be the backbone... The 3550's are housed at the top location (VLAN 20 - 2West). I thought about hanging the servers off the 3550's, but would then have to have gigabit cards in the servers, which I'm not sure we need (aren't the 3550-12G switches gigabit only? I thought I read that there are two version of the 3550. One that has 2 gbic ports and 10 10/100 ports and the other has 10 gbic ports and 2 10/100 ports. I was looking for the 10 Gbic ports so we can connect the closet switches elsewhere via fiber to the 3550's)...

Also, I assume I'm correct about not needing routers in the server and WAN blocks?

Thanks for your input!

New Member

Re: Switch Block Design

I would make the backbone and servers in the same VLAN. Also, the GBICs are, in fact, GigE only. However, the two 1000T ports (and the 10 ports on the other 3550 version) are 100/1000 capable, so you don't need to go to GigE NICs immediately.

With this configuration, you can keep all your Layer 3 switching in the core, with the two 3550s. This would mean that the GigE links are already on the local subnets in the LAN "blocks". So, on your drawing, the blocks would be extended up the WAN link to the GBIC slot on the core switch.

You know, I'm not totally sure the 3550's are Layer 3 switches. Your certain they are, right?

New Member

Re: Switch Block Design

Well, Cisco call the 3550 an "Intelligent" switch. Seems to me to be greatly suited to Layer 3 switching in small and medium sized networks...

New Member

Re: Switch Block Design

Yep, you're right. So, then the way I'd go is to extend each VLAN up the GigE link to the core switches, and perform all Layer 3 switching at those two devices. Further, add HSRP to both core switches to provide more fault tolerance.

If you'd like to update your drawing to reflect any revisions you've decided on, that might be a good useful for you...


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