Setting up VLANs - not using router on a stick or manual port assignment

[smithcolm]

Hi,

we are running out of IP addresses in our basic subnet.

we have an idea that we should seperate the servers and clients onto different subnets using Vlans.

I have got packet tracer running VLans using router on  a stick method / inter vlans over dot1q encapsualtion, but this is very cumbersome and manually intensive. - you have to setup each port on each switch for a specific vlan etc.

and you have to know which port goes where (physically tracing cables is just not going to be possible here!!  whoever cabled and setup the network here, did not do a very good job! :-)

is there anyway of having just vlans across all devices, traffic will be forwarded / routed accordingly.

we will only use DHCP on 1 subnet / vlan - for the clients comptuers, servers will be fixed IP.

Thanks

C

[John Blakley]

You can have vlans across all devices, but membership is determined by how the port is configured that leads to the host. If you have all of your hosts in your generic subnet, you could leave that on vlan 1 so you don't have to worry about them losing traffic. The problem is going to come in when you move, say your servers, to a different vlan. You have to have something to route it be it the router-on-a-stick method or a L3 switch that would allow you do routing.

If it's simply to impossible to reconfigure subnets with vlans, the other alternative (not knowing how large your company is or how you're laid out) is to put secondary addresses on your vlan 1 interface and create a superscope for your dhcp server.

HTH,
John

*** Please rate all useful posts ***

[smithcolm]

How would i put a second address on my router?

could i then leave out vlans and just change my DHCP scope and let the router worry about routing the traffic?

[John Blakley · Accepted solution]

Yes. You'd still be a flat network because all of the subnets are still in vlan 1, but it will work.

For the interface of the router that connects to the switch, we'll use fa0/1 for example, you'd do the following: (I'm assuming 192.168.1.1 is your primary address now.)

int fa0/1

ip address 192.168.1.1 255.255.255.0

So above is what you currently have, and then you'd put in these commands:

int fa0/1

ip address 192.168.2.1 255.255.255.0 secondary

ip address 192.168.3.1 255.255.255.0 secondary

Then, if you're running a Windows server, you'd create another 2 subnets: 192.168.2.0/24 and 192.168.3.0/24. You take your existing subnet scope of 192.168.1.0/24 and add the other 2 new scopes to create a superscope. When you run out of addresses in the 192.168.1.0/24 scope, you'd automatically roll over to the other scope within the superscope.

Be 100% certain that you add the secondary keyword on the above; otherwise, you'll cause an outage because the router will think you're wanting to change from 192.168.1.1 to a different primary ip address.

HTH,
John

*** Please rate all useful posts ***

[smithcolm]

when i enter

ip address 192.168.2.1 255.255.255.0 secondary

i get

Invalid input detected...

:-(

[mahmoodmkl]

Hi

Can you please let us know on which router platform u r trying this.

Thanks

[smithcolm]

I'm trying to test on packet tracer 5.3 first before i try it live.

but it will be going onto a cisco 2901 router

[mahmoodmkl]

Hi,

I am not sure whethe this going to work on packet tracer but to confrim i suggest u do it on real router.

U can just try whether the commands is working or not it will not harm u r network.

[smithcolm]

Hi,

yes, i can set up a secondary IP address on the interface on my 2901 router.

is it as simple as setting up this second IP address on this interface and then using this new subnet range as normal?

that would be very handy.

[mahmoodmkl]

Hi,

Yes this just like this.

As mentioend above u can start using this subnet for your systems.

Thanks

[smithcolm]

Hey guys,

Added a second ip to the interface gigaethernet 0/1

got a machine on that range and it worked straight away.

Cheers for that simple fix.