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We've got 2 HP Procurve 4000M switches joined by a trunk. Switch 1 is connected to a Cisco 2600 router which is connected to a T1. Internet traffic for hosts on switch 2 must pass through the trunk. We're now switching to Comcast who's given us 4 port SMC router.

I would like to connect each switch to the comcast router to reduce traffic on the trunk, but I don't want to create a loop. The switches support spanning tree protocol, but I don't know how this would work with the comcast router.

Would a triangle network like this work?

Thanks for any tips.

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1 Answer 1

Yes. That's what Spanning Tree Protocol is for.

I'd highly recommend reading up on it, especially improvements like RSTP and MSTP (since you're likely going to vLAN the Interenet traffic off, hope you don't intend to just connect a cable modem to your network directly).

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Thanks for your help. I wasn't sure if the Comcast router would also need to support stp. I had hoped to avoid ramping up on vLANs and I had been planning on directly connecting our network to the Comcast gateway. Currently our Cisco router handles NAT. Why would letting the Comcast appliance take over NAT change things? Sorry if I'm being overly naive; I only need to know these things every few years when we change providers. The rest of the time I'm writing software. –  Cole Tierney Mar 29 '12 at 18:35
I think you're talking about the same Comcast modem we have, and it doesn't do NAT. It's just a fancy modem. They expect you to connect it to a perimeter network or firewall/gateway device. We might be talking about different hardware, but it's worth double checking. The Comcast hardware doesn't need to support STP, but you'll want to configure the Switches to prefer the trunk explicitly. –  Chris S Mar 29 '12 at 19:32
Sorry; I should've described our comcast router in more detail. Ours is the Business Class SMC Gateway. It does do NAT w/port forwarding and has a built in firewall. In fact we are using it now along with our T1. The cisco has one interface connected to our soon to expire T1 and another connected to the comcast router which is on a separate LAN. So right now we have 2 layers of NAT, which is a little crazy. :) I'm looking forward to simplifying things when the T1 goes away. –  Cole Tierney Mar 29 '12 at 19:44

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