VLAN Setup - Basic Questions

[Dale Magnant]

Hello,

I am new to VLANs and am hoping someone can help me with a few questions regarding VLAN setup on the 2650 series switches. I've read through the HP documentation and done some experimenting, and remain confused on several points, particularly on the matter of assigning IP addresses to VLANs.

Presently I have four 2650's and a Netgear GSM7224 all tied together serving a single LAN 10.10.10.0/24. (One of the 2650s is located in another building connected by fiber) The gateway (10.10.10.1) for this network is the LAN port of a Sonicwall firewall which in turn connects to our outbound router. Most systems on the LAN have fixed IPs, though laptops are served by the firewall's DHCP. The four 2650's and one Netgear are as follows;

2650 Switch#1 IP=10.10.10.101
2650 Switch#2 IP=10.10.10.102
2650 Switch#3 IP=10.10.10.103
2650 Switch#4 IP=10.10.10.104
Netgear Switch#5 IP=10.10.10.105


Question:
My primary point of confusion concerns the relation of the IP configuration of the primary VLAN to the IP configuration of any subsequent VLANs.

For example, on the IP configuration page of my first 2650, I have a management IP of 10.10.10.101/24 and a gateway IP of 10.10.10.1. So, since a VLAN is by definition its own broadcast domain, can I use any addressing I want for a secondary VLAN, or am I bound in some way by the IP configuration of the primary VLAN? That is, lets say I wanted a second VLAN with IP 10.10.9.0/24 and I have an additional gateway of 10.10.9.1 configured on the Sonicwall - would the 2650 have any problem with this?

Question:
Could I create a VLAN with the same addressing, 10.10.10.0/24, as my primary VLAN? Could these two VLANs share the same gateway? Can any two VLANs share the same gateway?

Question:
Suppose I wanted to create a VLAN (call it VLAN2) on Switch #1 comprised of three or four ports. Let's say this VLAN would function in isolation - no need to speak with other VLANs, no need for any gateway connectivity. All ports in this VLAN would be untagged. All devices in this VLAN would have fixed IPs. Let's say I wanted this VLAN to be 192.168.0.0/24 Would this be possible?

Question:
The Netgear documentation indicates that it fully supports static VLANs. Is there any evidence which suggests there may be compatibility problems in using the Netgear with the four 2650s in a VLAN which might incorporate ports on all five switches?

Thank you very much for your patience and help.

[Joel Belizario]

Hi Dale,

Question 1 - No you are not bound by the IP configuration of the primary VLAN, what you need to do is ensure the ports linking the two devices are tagged in the appropriate VLANs.

Question 2 - No you cannot create a VLAN with duplicate addressing, you would create conflicting information in the ARP tables and the router / switch wouldn't know where to send traffic.

Question 3 - Yep no problems doing that. a VLAN is totally separate until you connect it to other VLANs via IP routing.

Question 4 - I don't see any issues if everything is configured correctly.

Here's a good article on VLANs for you:

http://www.networknewz.com/networknewz-10-20030725IntroductiontoVLANs.html

Cheers,
Joel

[Dale Magnant]

Joel - Thank you for the reply. Sorry to be so long responding.

I had a chance to do a little more testing. My plan was to try creating the most basic of VLANs as described in my third question in the original post. Again, the default VLAN is 10.10.10.0/24 with gateway - 10.10.10.1

So, I created a simple two port VLAN which I wanted to set up as an isolated VLAN - no gateway. So, after creating the two port VLAN I went to IP configuration to give it an IP of 10.10.9.0/24. It would not allow me to leave the Gateway field blank. So I tried 10.10.9.1 (even though I have no such gateway) and it would not take that either. So, it appears that it will not allow one to create a VLAN without a gateway.

Am I missing something obvious?

I am assuming that if I had a legitimate 10.10.9.1 gateway (which I should have set up in a couple weeks) the 2650 would accept this?

Thanks,
Dale

[Joel Belizario]

Can you elaborate on the steps you're using to assign the IP address to the VLAN?

I don't recall any requirement for a gateway when assigning IP addresses to VLANs on the ProCurve switches.

[J Vesterdahl]

Hello Dale.

I have several isolated VLANs in my network, and I have been as confused as you.

If you have isolated VLANs without gateways, you don't have to assign IP addresses in the switches for those VLANs.

In my network, I have several VLANs, but only one - the management VLAN - uses IP adresses in the switches.
IP addresses in other VLANs than the management VLAN are needed only if you must route between the VLANs. I even have some VLANs connected to the internet through firewalls, and of course the attached devices on that VLAN need IP addresses, but as long as the management VLAN works, your isolated VLANs may act as transparent networks.