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VLANS with routers


I need some help - I am learning networking and I want to ask some questions. I need to configure this schematic from start to end. First of all I want to find out about vlans in this schematic. Can I use them and do I need them? I know a little bit how vlans work, but routers confused me... If yes, how many of them I need?

I guess that I need vlan for each Network: Network 1, Network 2, Network 3

Also I need vlan for administration?

Sorry If these questions are stupid.



If Network 1,2 and 3 are each on a dedicated switch with a dedicated router interface then they could all be the default VLAN 1 since they don't share the same L2 domain. You could just as easily assign them unique VLANs just for administrative purposes, but then all the switch ports would need to be configured in that VLAN.

In instances where there are 2 or more networks sharing the same switch / L2 domain, then VLANs would be needed to separate them. In these cases you'd have multiple VLANs on a single switch.

You don't "need" a VLAN for administration, but sometimes it is a good idea. It's obviously simpler just to assign the switch an IP in the existing VLAN. It saves IP space and then you don't have to trunk to the router. Having a separate switch management / administration VLAN is better from a security standpoint along with other things, but it requires additional network space and trunking to the router.

Hope this is helpful.

Joseph W. Doherty
Hall of Fame Expert

Chrihussey has hopefully answered your questions, but I just wanted to note that Cisco's learning forums are more oriented to "learning"  then these forums which are more oriented toward operational networking issues.

Not applicable

It wasn't stated, but you're also going to need some /30 networks either between the ISP IPT1-R1/2 routers and the U1/2 firewalls then again between the firewalls and the R1/R3 in the grey network assuming you're also configuring the ISP network.  If you are, you'll also need some kind of routing protocol running like EIGRP to allow the routers to learn what networks are connected to what routers and how to route traffic efficiently.

Arturo Saucedo

No question is a bad question and if you can't get formal education grab a CISCO Engineering book and a Basics CCNA Lab book and work from it.

Cisco Employee

The hosts connected to your switch are in default vlan which is vlan 1.

You don't need vlans in you networks based on your illustration unless it tells you to separate the hosts or users connected to your switch in each network.

You can manage these hosts by creating new vlans and assign the ports of specific hosts in a particular vlan.

for example:  

Imagine that in network 2 you have 20 users connected to 1 switch.  10 users are in Accounting department and 10 users are in Sales department. If you want to separate/manage these users you can put them in different vlans. 

Create vlan 2 for accounting department and create vlan 3 for Sales department. However, users from different department will not be able to communicate to users on other department unless you configure inter-vlan a.k.a router on a stick or use a layer 3 switch.