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Beginner

VLAN real usage

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hy, i have a question regarding to vlans

so i have this network diagram which is of a standard , common layout of a network building with 4 floors with 100 or so devices on each floor

 

i have created a vlan for each floor VLAN2,3,4 and so on and i route all the traffic between vlans with my 1841 router

 

now, the question i have is this

 

is it worth bothering with vlans, knowing that if the host 1 wants to communicate with host 3 , all of the traffic must go to the 1841 and back, and it will consume more unnecessary bandwidth than if all the hosts were in the same lan?

i mean if there were only 1 vlan as it is by default and if the pc1 wanted to tansmit a very large file to pc 3, the traffic would not go to the router in a single vlan. i mean vlans are great, they isolate the traffic between hosts , but the downsize is that it consumes unnecessary bandwidth and if the pc 7, for example wanted to go out to the internet the speed of the connection will be slowed down because of the pc1-pc3 communications and so on.

 

so my question is this 

what is a better approach without using layer 3 switches?

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Hall of Fame Expert

Re: VLAN real usage

Hello silviu1983,

your understanding is correct and I totally agree on your concerns.

With four floors and having 100 users on each floor performing inter vlan routing on a SW based router like C1841 is a true bottle neck for performance.

 

You need an hardware based multilayer switch to perform inter Vlan routing and to use the router only for NAT and internet access.

even a SMB product like SG 350 or SG 550 is enough and the difference in performance is great  few hundreds Mbps on C1841 versus 10/20 Gbps on multilayer switch.

I would suggest you to buy and install a multilayer switch (L3 switch) for performing inter Vlan routing.

Otherwise you should create a flat L2 network using a single Vlan with 600 users and a single IP subnet. In this way the C1841 would be used only for internet access.

However, you can have issues with broadcast traffic and you have no way to control traffic between Vlans using ACLs.

 

I would go for the multilayer switch.

Edit:

I see in your network diagram that you have C2960 switches check if one of them is capable of basic routing if it is move inter vlan routing to it.

 

 

Hope to help

Giuseppe

 

3 REPLIES 3
VIP Advisor

Re: VLAN real usage

I m not sure why you created vlans per floor. But in most cases you find vlans split up in fynctions like data voice servers. 3rd party etc . I amnot sure what you re traffic pattersn are but nowadays most traffic will go offsite to datacentre and internet for things like officce 365. So your router would not really route that muchbetween vlans anyway
Please remember to rate useful posts, by clicking on the stars below.

Highlighted
Hall of Fame Expert

Re: VLAN real usage

Hello silviu1983,

your understanding is correct and I totally agree on your concerns.

With four floors and having 100 users on each floor performing inter vlan routing on a SW based router like C1841 is a true bottle neck for performance.

 

You need an hardware based multilayer switch to perform inter Vlan routing and to use the router only for NAT and internet access.

even a SMB product like SG 350 or SG 550 is enough and the difference in performance is great  few hundreds Mbps on C1841 versus 10/20 Gbps on multilayer switch.

I would suggest you to buy and install a multilayer switch (L3 switch) for performing inter Vlan routing.

Otherwise you should create a flat L2 network using a single Vlan with 600 users and a single IP subnet. In this way the C1841 would be used only for internet access.

However, you can have issues with broadcast traffic and you have no way to control traffic between Vlans using ACLs.

 

I would go for the multilayer switch.

Edit:

I see in your network diagram that you have C2960 switches check if one of them is capable of basic routing if it is move inter vlan routing to it.

 

 

Hope to help

Giuseppe

 

VIP Expert

Re: VLAN real usage

"what is a better approach without using layer 3 switches?"

Yes (for the reasons described by Giuseppe), in fact you may only need one (or perhaps two if you want "core" redundancy. (As also noted by Giuseppe, some 2960 models support very limited routing - which might be enough for you.)

Besides considering redundancy (as losing a network for 400 users if there's one device failure), you might, if possible, consider using gig links to your network "core" and further, also if possible, might consider more of a physical "star" topology, rather they your daisy chain topology.

BTW. depending on the bandwidth of your Internet connection, an 1840 might be rather small for that too.
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