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Router sizing question

Posted on 2006-06-30
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Last Modified: 2013-11-29
Hi, am in the process of sizing a router for a client. The environment is as follows:

Approx 230 XP desktop users
6 Cisco 2950 switches (currently not cascaded)
10meg Internet connx (leased line)
10meg LES10 to offsite ASP

At the moment all of the users are on the same class C subnet which, including the addresses used by the servers, is quite congested as you might imagine. My proposal is to introduce a router and create 3 VLANs on the switches; leave the servers on the current subnet to minimise reconfiguration of firewall rules and so on and transfer the users to the two other VLANs spread across the switches. The router would be responsible for getting data between the VLANs.

My questions are:

Would I need a 3 interface router? Or can I use one with less interfaces and just plug it into a trunk port on one or two of the VLANs and have the switches send the packets to the correct switch in the stack? Would 2950 switches be fast enough for this configuration?

If a 3 legged router is best, would it be sensible to get a 2 interface model and add another NIC? I haven't found many with 3 10/100/1000 NICs.

This isn't a big environment, but it's not tiny either. I'm looking for some space to expand too in the future. What series of Cisco routers should I be looking at? I've looked at the 2700 and 3800 series' so far.

Thanks in advance for any help.
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Question by:georgemason
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6 Comments
 
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Author Comment

by:georgemason
ID: 17017081
Having read a bit more I see that most if not all Cisco routers support 802.1q VLANs, meaning that potentially I could use a router with less physical interfaces than the number of VLANs. I guess though that I'll run into a problem running all that traffic through one interface, as the users are now used to a solely switched network, and would probably perceive this upgrade as a "downgrade"!
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by:lrmoore
ID: 17017748
You're on the right track, but you might want to consider a layer 3 switch instead. An L3 switch has all the basic routing capabilities of a router (minus some advanced stuff) to route VLAN "flows" at full wire speed.
With a router using vlan tagged sub-interfaces - yes you will create an artificial bottleneck in the network by trying to use it.
Something like Cisco's 3560 switch working as the backbone switch with all 2950's attached to it directly if you can. You can get the gigabit model and assuming the 2950's have gigabit uplinks, you can create a full gig backbone.
http://www.cisco.com/en/US/products/hw/switches/ps5528/index.html


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by:georgemason
ID: 17018007
I did think about layer 3 switching but thought it would be too costly. In this instance the 3560 would act as the controller for the other switches then?

Not sure if the 2950s have gigabit uplinks or not, but will check.
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by:lrmoore
lrmoore earned 62 total points
ID: 17019202
A decent L3 switch is less $ than a 3800 series router
The 3560 doesn't really "control" the other switches, just the VLAN's and the layer 3 routing between the vlans. It works best as a hub (as in hub-and-spoke) device with all the other switches hanging off of it.
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cooledit earned 63 total points
ID: 17029718
hi,  georgemason

Do not forget as soon as you decrease the broadcast domains you will also gain bandwith in this matter.
You could size each subnet for a max of 100 users and create more VLANS.

1.  so one VLAN fro servers as you suggested
2.  3 Subnets to contain 300 users also for future growth

a good solid backbone, switch many route once. Maybe since you are reorganizing the VLAN structure pick another subnet for experiment, future growth, IP telephoni or else..

Maybe you can also suggest to your client to get an additional line in as for failover "Loadbalancing", a second router solution.

As per lrmoore the 3800 series router does what you need 10/100Mb WAN, 1000MB Lan Ethernet.

Cooledit
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by:georgemason
ID: 17035967
Thanks to you both. The customer has many many issues which need to be addressed so I think this one might get sidelined for a little while, but I think either a L3 switch might be the way forward. I do intend to put in 100-150 users per VLAN and add space for growth as the company has seen rapid growth in the last few years.
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