VLANs and multiple subnets

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Feb 23rd, 2008

I have this problem too.
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lamav Sat, 02/23/2008 - 10:46

hello:

I have no clue what you're asking. This is the most UNinformative question I have ever read on here. LOL

I think I got what you want to ask, though.

The answer is YES, you can have multiple subnets in one vlan.

Typically, each subnet is its own broadcast domain and if you have 1 subnet per vlan configured, then that vlan is its own broadcast domain.

If you have multiple subnets in 1 vlan, all the subnets are in the same broadcast domain.

Example of single subnet vlan:

interface vlan 10

ip address 10.10.10.0 255.255.255.0

Example of 2 subnets in the same vlan:

interface vlan 10

ip address 10.10.10.0 255.255.254.0

In the second example, subnet 10.10.10.0/24 is one subnet and 10.10.11.0/24 is the other.

HTH

Victor

Anonymous (not verified) Sat, 02/23/2008 - 13:36

Anonymous (not verified) Sat, 02/23/2008 - 13:36

Anonymous (not verified) Sat, 02/23/2008 - 19:07

Anonymous (not verified) Sat, 02/23/2008 - 19:29

Victor,

I'm having trouble replying, hence the multiple blank replies. Trying from another machine now.

Anyway...

I'm aware of option #2. However, it would require us to reconfigure a lg number of printers and switches. I have found that the default gateway on all devices would need to point to the vlan.

I was hoping that there was a way to have devices dynamically assigned to a vlan - based on their subnets. So a device using 10.10.10.x would be placed on vlan1, another device using 10.10.20.x would be placed on vlan2, etc. And this would need to happen without knowing which ports those machines might be on, ie dynamically.

Is this doable with nothing but a single dhcp server that doles out ips in 3 subnet ranges, one l3 switch, and a whole bunch of l2 switches?

Thanks,

Carol

lamav Sun, 02/24/2008 - 06:47

Hi, Carol:

Im afraid the answer to your question is no.

Devices can be assigned to a vlan statically, based on the switch port's configuration, or dynamically, with the use of a VMPS server, where the device is assigned to a vlan based on its MAC address. So, any port you plug the device in will render it a member of the same vlan.

Devices are not assigned to a vlan based on their subnet.

Then, the vlan a device belongs to defines the scope of IP addresses from which it may be asssigned an address, not the other way around. Moreover, the default gateway the device uses will be the ip address assigned to the routed L3 interface for that vlan.

I hope I have helped you.

Victor

Anonymous (not verified) Sun, 02/24/2008 - 09:34

Anonymous (not verified) Sun, 02/24/2008 - 15:05

Aaaaaaaaaagh!

I am having major difficulty trying to post my replies :(

Anyway...

Victor, thank you for answering my question. I suspected the answer was that it couldn't be done, but my boss insisted I get a second, more expert opinion.

Consider the case closed.

lamav Sun, 02/24/2008 - 15:07

LOLOL...its a new secret anti-terrorism font. lol

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