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Basic VLAN question

C

Cooky

Golden Member
Right now we have a flat network and I'm planning to segment it into several VLANs. I know in large campuses each VLAN is a separate subnet, but our network is not very big.

My question is would it be ok if all the VLAN's belong to the same subnet? What are the pros and cons in your opinion?
 
they have to be separate subnets.

That's where the router comes into play - to route between the VLANs. Without a router the VLANs are completely separate and cannot communicate with each other.

General rule thumb for sizing VLANs is 200 or so hosts per VLAN. Usually they have a 255.255.255.0 mask.
 
Spidey, thanks for the quick reply.
We have 2 Cisco cat3560's and 1 cat4506, all are capable of layer3 switching between the different VLANs and I do know how to do it if the VLANs are in different subnets.

I'm trying to avoid any extra work for assigning them to different subnets, IP scope change, DHCP, etc because the network is too small to go over all those trouble.
I guess there's no other ways around?
 
nope.

you'd be moving nodes to a separate layer2 network (vlan) so they'll need new ip addresses. the DHCP stuff/scope is a piece of cake and only takes a few minutes to configure. Just don't forget that you'll need a DHCP relay agent (ip helper-address command) on each of the VLAN interfaces.

just try to keep layer2 and layer3 mapped out and it should get real clear. For simple networks like this its always good to have a server vlan and a user vlan
 
and also turn off the IP forward protocols that you don't want forwarded.

like netbios, etc. I normally turn them all off except for DHCP.

I just don't want any broadcast forwarded ANYWHERE without me knowing about it/wanting it.

no ip forward-protocol udp <option>

Oh, and you'll need to setup a WINs server as well.

😉
 
We already have a WINS server in place and I think clients should be able to find it since the WINS info comes w/ DHCP assignments...please correct me if I'm wrong.
What I didn't get though, is you said you turn off any unwanted broadcast including NetBIOS. Isn't NetBIOS needed for WINS?

I've read some contradicting articles saying if you don't stop the NetBIOS forwarding, you'll get some WINS errors w/ "master browser reelection" of some sort. So I guess it's better to turn it off anyway?
 
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