Which router to create a second subnet?

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Mar 20th, 2008
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We have just bought a new site adjacent to our current site and need to bring it onto our network. We currently have 1 subnet at present so no routers. The new subnet will host up to 50 users. Most servers will stay on the original site so there will be a fair bit of data coming over from the new site and all phones on the new site will be VoIP.

Looking at the Cisco kit and around the net I was thinking of the Cisco 2800 series. I know these units are all modular so was hoping for some advice on what I would need to spec on the box as I am unfamiliar with terminology. I was going to run two cables (Cat6e) between the sites (in case one ever suffers a break). The router would be on the main site and would need to have two RJ45 ports - one to connect to the existing office subnet and one to connect to the new office subnet. Is this standard on the 2800 series or do I need an additional module that hosts these two ports?

For future needs I was also wondering if it would be worth specking the two ports on the router at 1000Mb/s rather than 100Mb/s if that option is available.

I was hoping for some advice to see if I am going down the correct lines or if there might be a better solution on offer.

Many thanks for any assistance given.

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Overall Rating: 4 (1 ratings)
Joseph W. Doherty Thu, 03/20/2008 - 04:28
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Most of the small routers, i.e. 38xx and smaller, might disappoint you in their LAN routing performance, especially if you're thinking of connecting gig links. (You did expect to connect Ethernet between the buildings, correct?) If you're doing pure LAN routing, a L3 switch would perform much better. I would suggest you examine the 3560 and 3750 series.

b-corkindale Thu, 03/20/2008 - 04:40
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Thanks - I didn't know you could do routing on a switch - I'll take a look at those models. It is the intention to connect the buildings with Ethernet as they are less than 100 metres apart.

Do the models you quote come as standard with the ports to create two subnets or do I need a seperate module along with the card?

Joseph W. Doherty Thu, 03/20/2008 - 05:15
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They come with Ethernet ports, often mainly copper (perhaps like your existing switches) and often with SFP Ethernet ports (where you can use fiber). You define VLANs on the them, usually one subnet per each VLAN. So, two subnets doesn't require any additional hardware.

b-corkindale Thu, 03/20/2008 - 05:36
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I am therefore assuming the switch is setup as a default gateway?

If not and the switch intelligently routes between VLAN's then this would not work. I have 8 or so older 3com switches on the network. Clients hooked up to these would need to reach the new subnet therefore would need to see a default gateway to get there.

meballard Thu, 03/20/2008 - 21:51
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FYI, a layer 3 switch is basically a layer 2 switch with the addition of a router built in. A full router has some additional features, primarily useful in WAN situations, but for your purposes (routing between two sites connected with Ethernet), a layer 3 switch will do quite nicely (and perform better).

You might want to consider fiber between the sites, on longer runs like that it would probably be more reliable.

i-kendall Thu, 03/27/2008 - 14:10
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Have a look at the Cisco Catalyst 3560-8PC. It has 8x10/100 ports plus one gigabit ethernet copper port and you can also use a fibre SFP module instead. You should really use fibre if the buildings are not physically connected, to provide electrical isolation and freedom from any interference problems.

In the UK the 3560-8PC are about £530 each, less than a router. Configure them with VLANs for the users and for the VoIP, also you need to configure QoS to ensure voice quality.

As you said, the L3 switch should be the default gateway for each VLAN (subnet). Then configure a default route on the switch for Internet access.

I can help with the config if you need, but you may wish to take that out of this forum ?

b-corkindale Mon, 03/31/2008 - 02:53
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Thanks for your kind offer of help. We now plan to run fibre between the buildings though we are now going to run a 50 pair so we can use our existing phones without switching to VoIP. Once we have the cables in place I will decide which switch to go for and may look you up for help if I get stuck.

Thanks again.



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