How should I structure my LAN?

The Netgear GSM7248 is not stackable, therfore you will have a bottleneck at your uplinks.

I have a GSM7352 at the top of a stack, which is stackable with a 24-gigabit cable.  Same slot could be used for 10GbE, if you had it.

Are these purchases recent enough to consider exchanging for a stackable model?  Yours is more of a standalone or core router.  Stacks will act and manage as one unit.  Also, the stacking cables offer far greater bandwidth than uplinks with patch cables.

Gigabit switches (even un-managed) are generally sufficient for most small offices.  You could increase your uplink speed by creating a LAG (link aggregate group) of ports.  This gives you a 2Gbps link between switches.

If you are stuck with these switches, I suggest getting the physical layout done before worrying about VLANs and QoS.  Those are icing on the cake.  You need the basic recipie.

You'll have to find out what your true bandwidth need are.  CAD and rendering are not bandwidth intensive if the functions are performed locally.  Does the application engineer have a spec for you on network bandwidth consumption?

Without that information, here's a general recommendation:

The CAD workstations can also use two gigabit ethernet links in a LAG, which is better than just ALB.

In terms of AV software; I recommend ESET Nod32.     Not to say there is a virus infection for sure.
How many workstations are there in each department?
How many servers need to be used by each department?

Are there any specialty network apps in use other than say standard e-mail, surfing, sharing/downloading/uploading of reasonably sized office documents?


It may be helpful to compile an estimated  amount of traffic usage expected
for each department at various times of the day based on  per-user  usage
estimates AND total number of users/workstations



The single best thing you can do other than having plenty of inter-switch bandwidth, and have good wiring is to have managed switches that have some intelligence, and can provide you with information  about where traffic is coming from.

If your switches are managed switches such as  Cisco 45xx  units that provide monitoring functions,  you might setup a span session on a port,  and plug in a laptop running wireshark, to the monitoring port, turn the port on, at times when network usage should be minimal (but have PCs turned on), as a method of detecting unusual traffic.

This may also assist in seeing if there are background apps running hogging network bandwidth, and if they are essential to the business or dispensible in the name of network performance  (although when it comes to internet traffic, it is preferable to monitor that at a firewall).

Ideally: have managed switches that support SNMP-based interface statistics,  enable SNMP, setup a SNMP community, and have a server or workstation graph traffic on the inter-switch link ports 24/7, for assistance in locating bottlenecks.   There is useful free software such as MRTG and Cacti  that can help with this on a *ix server.   Or  commercial software like Intermapper  you can use on a Windows workstation.    The  "high-end" extremely expensive solution being tools like Solarwinds'  suite or HP Openview, full-blown monitoring packages.

(For security reasons,  set aside a special VLAN for managing
network equipment  and restrict access by ip to your approved management
stations)


For 5 departments, you probably do not need a super-powerful core switch, or $10,000 monitoring system.  In the absence the most likely bottleneck are your inter-switch links.

You should check vendor specifications for the specific models of
switches you are using for maximum total gbps traffic,  and be sure you are using
non-blocking switches, if you want maximum performance.

I  prefer  Cisco's  multilayer switches,  but  brand isn't all that important.
Make sure they are commercial-grade units with SNMP management and
full layer2 and layer3 capabilities,  no  5-port unmanaged linksys boxes should
be allowed on the organization's premises.

The portable 5-port devices should be regarded extremely as dangerous, especially in the hands of the computer illiterate,   who have an insidious  knack at creating bridging loops or  "accidentally"  introducing  unauthorized DHCP servers  and
rogue home routers with a "192.168.1.1"   ip conflicting with your network's gateways.

To that end, switches with port security, and ARP inspection/DHCP snooping capabilities  (to allow only the privileged ports to dish out DHCP) may be
administratively useful  to minimize problems later.

Admittedly  using VLANs does have some administrative overhead;
whenever  a new office is to be plugged in,  a switch technician needs to
assign the port to the right VLAN.

One possibility is to pre-allocate certain banks of ports to certain VLANs.
From a security standpoint though, it is best to have unused ports turned off.

When a new authorized device is being connected to a switch,
proper documentation should then be entered and filed with the request
for a  switch tech to turn on the new port.

Just to clarify something that may not be obvious:  if you use VLANs,  you don't need every switch to be multi-layer.

You can use mostly Layer2 switches and have one  multilayer switch as a central switch  plus possibly a backup  to  provide inter-VLAN routing   and connection to your ISP's equipment.

Multilayer switches are much more expensive, and it's better to spend that cash
on pure forwarding speed than on L3 capabilities, when only one device can handle
it.

But keep in mind you shouldn't want a lot of inter-vlan traffic coming back to the same L2 switch (on a different VLAN)

So this works optimally if the departments/VLANs are mostly concentrated on their own switch.