Why use a VLAN?

Hi all

I work for a medium sized college (1500 students) and have around 600 nodes
on our network. We currently have a subnet mask of 255.255.248.0 which gives
a flat IP range. We don't have a huge issue with security (we have two
seperate domains - going to one in 6 months) but it has been suggested we
move to using VLAN's.

What would be the benefit for us and anything which may cause problems?

Thanks in advance

Chris

"Chris Pratt" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I work for a medium sized college (1500 students) and have around 600
nodes
> on our network. We currently have a subnet mask of 255.255.248.0 which
gives
> a flat IP range. We don't have a huge issue with security (we have two
> seperate domains - going to one in 6 months) but it has been suggested we
> move to using VLAN's.

The question isn't VLANs,...the question is Subnetting. Once you decide to
subnet it doens't matter if it is VLAN or Physical Segments,...they both
accomplish the same thing, so you would use whatever is easier to do in your
situation. VLANs tend to be more difficult to "wrap your brain around"
because they perform the same task in the "virtual world" instead of the
physical. Physical is easier because you can just look at it and see what
you are doing. Because VLANs share the same physical wire with multiple
subnets they are not as "traffic efficient" as physical segmenting which
runs only one subnet over a single wire. In real life you usually end up
with a "hybrid" of the two.

The benefit? Well, there may not be one. Segmenting networks reduces the
effects of broadcasts by iscolating the scope of broadcast into smaller
sections of the network called "broadcast domains". Since the effects of
the broadcasts are reduced it leaves more "room" on the wire for normal
non-broadcast traffic. They can also help with security by running ACLs on
the Routers that sit between the segments.

So if you are experiencing congestion due to the amount of broadcasts then
Segmenting will help you, otherwise you won't see any improvement other than
maybe the security benefit. Now I typically like to keep the number of
Hosts below 300 per segment, but I don't know of any "hard" numbers,...it
pretty much depends on what you have happening on the system that might
generate a lot of broadcasts.

Now if you have congestion from a lot of just general traffic, this would
result in a lot of Collisions. To solve that you would use Switches which
segment the network into Collison Domains. You would just replace all the
Hubs with Switches and you are done.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

Thanks Phillip. That was very informative and very helpful

Thanks again

Chris

"Phillip Windell" <@.> wrote in message
news:(E-Mail Removed)...
> "Chris Pratt" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> I work for a medium sized college (1500 students) and have around 600
> nodes
>> on our network. We currently have a subnet mask of 255.255.248.0 which
> gives
>> a flat IP range. We don't have a huge issue with security (we have two
>> seperate domains - going to one in 6 months) but it has been suggested we
>> move to using VLAN's.
>
> The question isn't VLANs,...the question is Subnetting. Once you decide to
> subnet it doens't matter if it is VLAN or Physical Segments,...they both
> accomplish the same thing, so you would use whatever is easier to do in
> your
> situation. VLANs tend to be more difficult to "wrap your brain around"
> because they perform the same task in the "virtual world" instead of the
> physical. Physical is easier because you can just look at it and see what
> you are doing. Because VLANs share the same physical wire with multiple
> subnets they are not as "traffic efficient" as physical segmenting which
> runs only one subnet over a single wire. In real life you usually end up
> with a "hybrid" of the two.
>
> The benefit? Well, there may not be one. Segmenting networks reduces the
> effects of broadcasts by iscolating the scope of broadcast into smaller
> sections of the network called "broadcast domains". Since the effects of
> the broadcasts are reduced it leaves more "room" on the wire for normal
> non-broadcast traffic. They can also help with security by running ACLs
> on
> the Routers that sit between the segments.
>
> So if you are experiencing congestion due to the amount of broadcasts then
> Segmenting will help you, otherwise you won't see any improvement other
> than
> maybe the security benefit. Now I typically like to keep the number of
> Hosts below 300 per segment, but I don't know of any "hard" numbers,...it
> pretty much depends on what you have happening on the system that might
> generate a lot of broadcasts.
>
> Now if you have congestion from a lot of just general traffic, this would
> result in a lot of Collisions. To solve that you would use Switches which
> segment the network into Collison Domains. You would just replace all the
> Hubs with Switches and you are done.
>
> --
>
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
>
>