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Layer 3 switches

Posted on 2010-01-10
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Last Modified: 2012-05-08
Our school division is made up of seven schools. All schools point back to the central office location where all Internet traffic comes through. I have to setup subnets and VLANS at each school. Do I just require one Layer 3 switch at each school for this configuration as well as at the Central Office? Can the other switches be layer 2?

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Question by:skenny10
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13 Comments
 
LVL 22

Expert Comment

by:chakko
ID: 26281069
More information about your network would be good.  

I am guessing a simple hub-and-spoke topology, sites are connected by some type of WAN link with routers.

You shouldn't need any layer 3 switches at the schools (if they have 1 logical LAN at each school).  You could get by with Layer 2 switches if you want.  


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LVL 13

Expert Comment

by:GuruChiu
ID: 26281099
I have a customer who may have similar situation as you do. My customer have a L3 switch at the district office, which have single mode fibers to each of the 13 schools. For smaller schools, they are using just L2 switches. For bigger schools, they do have L3 switch at the main phone room, which connect to other L3 switches.

The DO L3 switch is enough to have a sound network. The additional L3 switch in bigger schools is because they are using VoIP and the L3 switch and off load local routing. Also L3 switches are much less expensive now.
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Aaron Street earned 1500 total points
ID: 26281596
YOu dont need a layer 3 switch if you have a router that you can set up to route VLAN at each school.

However you may find it a bit simpler to do with a layer 3 switch if you want mautiply vlan/subnets at each school.

The benifit of a layer 3 switch is keeping the routing and vlans on the same device.

however as long as you have a switch that can form VLANS, you could do the intervlan routing using the current on site router.

Check if the Routers at the schools can run router on a stick model. if they can you dont need layer 3 switching.

if they cant then you will need a device to router between vlans (if you use mutiply vlans at each school) this can either be a seperate router or a layer 3 switch.

All a layer 3 switch is is a switch that can also do routing (there is more to it than this but this is the fundemental point). So if you need to do internaly routing with in each scholl then you may want to look at a Layer 3 switch.
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LVL 8

Expert Comment

by:bsohn417
ID: 26282938
Having layer 3 at each school will make your work lot easier.
with layer 3 u can create VLANs and trunk back to layer 2

it will be also easy for you run routing protocol such as RIP,OSPF,EIGRP.

you need SW model #

u should look in to Cisco 4948 (get the most out for price), Cisco 3650 or stackable 3750.
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LVL 21

Expert Comment

by:Rick_O_Shay
ID: 26283023
Without more details I don't know what kind of links you have between the Central site and the schools but you might want to consider using the L3 or router solution at each site so you aren't sending every broadcast from every VLAN across those links. To summarize, if you use L2 on those links you will be loading them up with a lot of unnecessary traffic compared to using L3 and only sending required site to site packets.
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Author Comment

by:skenny10
ID: 26283646
Previously it was a flat network with just a DSL modem at each school and only a router at the central office. Now, there is a fibre connection at each school. Three of the schools have a router (Lanspan IP) while the other four do not - Lanspan (and there is a router at the central office as well).

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LVL 16

Expert Comment

by:Aaron Street
ID: 26283758
The links between sites are going to require routing. I would be shocked if a school ran layer 2 trunks between sites, so you would never besending broadcasts across these links any way...

ITs simple

IF you have a single VLAN at each school, then a LAyer 2 switch will be fine. (you will also need a router but you will need this even with a layer 3 switch)

If you want to run mutiply VLAN's/subnets then LAyer 3 might be an option, however if traffic is quite low and your current router can route the VLANS (IE can run router on a stick) then again you could get away with LAyer 2 switchs, (As long as they can create VLAN's, which most managed switchs can do)

This would be a cheap option to follow..


However if you have/expect high data through put between the subnets at with in a site. This is where a layer 3 switch comes in to its own. Rember a layer 3 switch will not be able to route traffic directly between sites (most sites use leased lines, adsl, ISDN framrelay or other protocols to move data between sites, Layer 3 switchs can only handle ethernet traffic IE. internal data) you will need to have a WAN router to do this. many of these can also route data batween your vlans. And this can often be the cheaper way to do it.
VLANS and trunks are not layer 3! LAyer two switcsh will do these fine.
purchasing 7 layer 3 switchs could set you back a fair bit of money, espicaly to get ones that will cover your layer 2 needs in to the future. If you already have routers and switcsh installed at the schools, I would look at using this current equipment to get what you want before purchasing any more. You can always purchase layer 3 switchs at a later date and upgrading to them will be simple.
Look up router on a stick for ideas of how it is set up, and let us have the model numbers of your current routers and we can suggest if these would be sutible for running all the routing for the sites.
My advice is don't spend money while you can do some testing with what you have, once you have set it up you will have a good understanding of if you require layer 3 switching or not, and if so at what sites.
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LVL 16

Expert Comment

by:Aaron Street
ID: 26283815
Folloing up on that post I can see you are running basic routers at the moment.

I am assuimg the LANSPAN routers are providing an ethernet termination at each site.

In this case LAyer 3 switchs could be a good idea. but again not essential.

LAyer 3 switchs are limited in terms of features compared to WAN routers (IE no security such as VPN's, and more limited feature sets of wan protocols)

on the up side hey are much faster than a dedicated router and simpler to configure...



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LVL 21

Expert Comment

by:Rick_O_Shay
ID: 26283837
So probably gig fiber between sites? That may be enough to not have to worry about but things, especially bandwidth usage, have a way of growing over time and you don't want to waste any with broadcasts. It's usually a cost issue but L3 swiches at all sites would give you the most flexibility and best potential for the future for things like QOS and other traffic management, etc.
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Author Comment

by:skenny10
ID: 26284079
All of the schools in our division are part of one domain on the administrtive side of the network.  As well, we run a  terminal services server at our high school for our Student Database Management system that all schools access from their own location. Would this scenario make it necessary to go with the layer 3 switch or is the layer 2 still OK given this requirement?
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LVL 16

Expert Comment

by:Aaron Street
ID: 26284284
Skenny,

I am not quite sure you understand.

a layer 2 switch + a router

will give you exactly the same funcanality as a layer 3 switch. (Thinko fo a layer 3 switch as a layer 2 switch with a built in router attached)

The question you need to establish first is do you need to run seperate subnets on the same site?

once you have decided this you then needto look at the proformance benifits of using layer 3 switchs aginst the cost saving of router/layer 2 switch.

And with out knowing users numbers, traffic amounts and other things its very hard to tell you which one to go for.

But layer2 switch + seperate router = layer 3 switch in terms of funcanility.
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LVL 21

Expert Comment

by:Rick_O_Shay
ID: 26284462
Basically it is a question of where do you want the routing function for each remote site to be done, at the core or at the schools? And if you want to do it out at the schools is the cost to add L3/routing there within your guidelines. You can configure to get to all of your shared resources either way.
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Author Closing Comment

by:skenny10
ID: 31675371
good
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