Designing a new small network

Unanswered Question
Apr 19th, 2008


We are in process of starting our new branch office. This office has one 1841 router, two 3750 switch and 3 Cat500 switch. Could anyone give the best possible way to connect it together . Requirements are Core switch redundancy,VLANs must be enabled,DSL connection to established. Diagram of the network has been attached.

Thanks in advance

I have this problem too.
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Joseph W. Doherty Sun, 04/20/2008 - 04:34

One recommendation for connecting your devices would be to "stack" the pair of 3750 and connect one uplink from each Cat500 to each 3750. The pair of uplinks from each Cat500 to the 3750 stack would be configured as a Etherchannel. If you plan on having multiple VLANs extended to the CAT500s, then the Etherchannel would be also configured as a trunk.

You didn't note the particular model of Cat500 or 3750. Hopefully you'll be able to run the Cat500 uplinks at gig speed. Copper if distance permits, otherwise fiber.

If you will have multiple VLANs within the 3750 stack, enable routing. (If you only have one internal subnet, you could do all your routing on the 1841, but would still be good to enable routing on the 3750 stack, better positions you for routing between LAN VLANs.)

Between the 3750 stack and the 1841, again you should run a link from each of the 1841's Ethernet ports to each member of your dual 3750 stack. You can Etherchannel between some 2800/3800 Ethernet ports and 3750s, don't know whether this could be done with your 1841. If it could, beside making an Etherchannel between the 1841 and 3750 stack, you could also trunk all VLANs to the 1841 (I assume it supports trunks). The 3750 would be the default gateway for your VLANs with a default route to the 1841.

If it's not possible to Etherchannel between the 3750 stack and the 1841, you'll need to route across both links. If the number of subnets is small, you might just use static routes, or perhaps RIP.

Sushil Kumar Katre Sun, 04/20/2008 - 21:40

Hi Nazir,

I would suggest to have 3750 switches stacked together.

Have two uplinks from each of the CE500 switches, going to each 3750 switch and configure etherchannel.

Have multiple VLANs configured on CE 500 if required and configure routing on 3750 switch.

Have Layer 3 Uplink from 3750 switch to 1841 router. Each 3750 swich can have layer 3 uplink to the router. You can either have static routes configured on 3750 and 1841 or use RIP being a small setup. I'll prefer static routes.

>> Sushil

l.mourits Wed, 05/07/2008 - 00:40

I agree with most Sushil writes, except for the static route part. Consider this before chosing between dynamic and static routing. Are you planning on having redundant uplinks to your WAN in the future. If yes, then go for dynamic routing rather then static, that way adding the redundant wan connection is going to be easier.

In such case, also consider using aseparate vlan for the route protocol exchanges bewteen the 3750 and 1800 series router.

Other then that, just what Sushil says ;-)




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