Subnetting and VLANs

Posted on 2009-05-18
Last Modified: 2012-05-07
I have a network that has some issues at the moment.  There is a lot of traffic on one subnet  being.


So I just purchased two HP Procurve 2900 switches that supports VLANing.  I want to keep my servers on the current subnet and I understand with the Mask I have and a Class B address I can use 2.0, 3.0, 4.0, and so on for additional networks for my users, printers, VoIP, and so on.

However, my question is say I change my users to be:
What is my GW?  Do I have to set this as the VLAN IP address?  Can it talk to the 1.0 network?

Question by:Goofdru
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Expert Comment

ID: 24418192
You need to enable IP routing on the switches (providing you got models that support some layer 3 forwarding). Yes, your gateway will be the IP address of the VLAN interface.

Yes, it will be able to.
LVL 13

Expert Comment

ID: 24418196
Your gateway would be

Accepted Solution

equarando earned 250 total points
ID: 24419287
If your switches are layer 2 only you can use the "router on a stick" method.

step 1.) Setup sub-interfaces on your router (ex.) fa0/0.10 for VLAN 10 fa0/0.20 for VLAN 20 and so on... and use the command "no ip address" on the real interface on the router.
step 2.) make sure to set the encapsulation to the same as what the switch supports DOT1Q or ISL
step 3.) Assign IP address's and subnet masks to each sub interface (these IP's will be the gateways for each VLAN).
step 4.) The link to the router must be setup as a trunk (DOT1Q or ISL encap)

Now if I remembered everything correctly you should be able to talk between vlan's now.
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Author Comment

ID: 24421356
So if my shares are on and my users are in the range of - 254, they can access the shares with no problem?  Any routing done special?

One thing I was thinking was that I got an extra NIC in my file server as well, could I set it up to be on the user subnet as well and leave the current NIC tied to the iSCSI shares it is bound too.

I am trying to isolate traffic because I am running an SNMP trap (PRTG) and there is about a 5 - 15 second drop in communication on 4 of my servers at random times durning the day.  I think it is due to the iSCSI traffic and user traffic going through the same network.


Expert Comment

ID: 24423269
If you setup what I mentioned above, it should work. You will not need to setup any routing protocol because all of the networks will be "directly connected". So as long as you point the pc's/servers to the correct gateway (ip of the sub-interface) on their respective vlan.

Assisted Solution

akalbfell earned 250 total points
ID: 24424743
A few things.
You should absolutely get that iscsi traffic into its own VLAN.
I know you are using a class B range (172.16.x.x) but you are using it with a Class C Mask so for all intensive purposes look at it like you have just a Class C.
You can keep your PC's in the network they are in, and then add another network/VLAN of  but you will need to do routing to get all machines to talk to each other. One option is router in a stick which equarando already explained or the switch can handle routing if it supports it which Quori said. I am not familiar with those switches but looking at the site it says they support Layer 2 switching with static and RIP IP routing so i assume you can just create some static routes and it will do what you need. Maybe someone more familiar with the ProCurve switches can confirm that.

not sure how many servers and pc's and what kind of traffic you got around the network but at the very least move the iscsi traffic into its own vlan and you dont have to worry about any routing between networks because the point is to seperate that anyway

Author Comment

ID: 24425426
I believe I understand what equarando is talking about but the terminology used DOT1Q or ISL may be something different in my Sonicwall.

Also, the iSCSI traffic is between a EMC Celerra and 2 Dell servers, so without changing the bound addresses on the EMC box  I was going to leave the 172.16.1, network for the iSCSI but now that I think about it that is only 3 devices instead of changing all my printers, users, and my exchange, I can just change them and it be fine.

I am just nervous about this, mainly because it took me a month to figure it out.  Now that i konw the problem and have got the equipment to handle it, I am not sure if i am going at it right.  I would like to have 4 VLANs, 1 for servers, 1 for iSCSI, 1 for VoIP (future), 1 for Users/Printers.

Expert Comment

ID: 24425623
so the PC's connect to the switch which connects to a sonicwall?
That sonicwall cant handle routing so unless the Procurve switches you have can, you wont be able to have data flow between VLANs. for that you would need to add a router between the switch and the sonicwall.
its always a pretty big project to redesign a network, best done on a weekend when you have plenty of time to get the work done and test everything. My suggestion would be use the procurve switches you have now to test out in a mini lab. Setup your Vlans, connect 1 pc to each vlan and see if you can get the comupters to communicate. Once you get that down everything else should fall into place and you can always come back for help.

As far as ISL vs DOT1Q...ISL was created first by Cisco and is their proprietary protocol for trunking but DOT1Q is better and can be used on all different equipment. even Cisco would say its better since some of their equipment doesnt even support ISL. :-)
you really dont need to worry about that now though

Author Comment

ID: 24425926
The Procurve supports Routing I am almost positive.  I had called their suport and asked them how to do so and they were saying that I can set the VLANs IP address to be the default gateway of the subnet and that the switch would handle the traffic.

Yes unfortuneately I believe my Memorial Day will be spent here.

Expert Comment

ID: 24425965
yes like i said you can using RIP or static routes. Here is a PDF from HP about how to set it up
you could prob get most of the legwork done without having to install anything and then just put it all together over the weekend. Save yourself a little time in the office on a holiday weekend :-(

Author Comment

ID: 24426155
Thank you both for you help, I have plenty of reading and planning to do.  I may be over thinking this but at least I am thinking about it.

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