How to change access VLAN?

[Charger1129]

Hello! I have a network currently configured with my data VLAN on the default  VLAN 1. I Would like to  change this to VLAN 20  Without impacting the network as little as possible.  Is there anyway this Can be accomplished?

[Reza Sharifi]

Hi,

When you change a port from one vlan to another, there will be a short outage.  If you want to go from vlan 1 to vlan 20, you can create vlan 20  and the corresponding subnet ahead of time and during a maintenance window change the ports from 1 to 20.  All is required one command on the access ports. If you have a trunk port you also need to add vlan 20 to your trunk port.

HTH

[fogemarttt]

Yes, AS reza said,

you have to create your vlan 20 first with all the configuration. 

you will have a little shortage. to change to vlan 20. on the different interfaces, you can put

switchport access vlan 20 

on trunk interfaces, where you want to allow vlan 20 you must modify your command to add vlan 20. 

switchport trunk allowed vlan 20, etc...

The vlan 1 is native vlan by default, so you do not need to specify the switchport access vlan 1 by default. so that is the command which can make the difference. 

Regards,

Please if it's what you want !!!

[InayathUlla Sharieff]

Answers already been provided. Another quickest way:

Conf t

Vlan 20 >> create vlan.

2) Identify which interfaces you want this vlan to be put onto and make use of interface range command which would save your time rather than configuring each interface:

eg:

interface range f1/-24

Switchport access vlan 20.

3) Adding the vlan to the trunk port:

In case if you have already running some vlans on the trunk port then you just need to add this vlan 20 on to it"

Eg:

int g0/1 >> trunk port

 switchport trunk allowed vlan add 20 >> this will add vlan 20 to the trunk port.

HTH.

[Charger1129]

Thanks for the help everyone! 

Another question to go along with this. If I was to create a new VLAN along with a dedicated subnet for the VLAN, how could I tell that VLAN to use that particular subnet from my Windows DHCP server? And NOT the default subnet I already have set up on that DHCP server? 

[InayathUlla Sharieff]

You would be configuring ip helper address under that vlan right?

Kindly check the below link to get some idea:

http://www.freeccnaworkbook.com/workbooks/ccna/configuring-an-ip-dhcp-helper-address

HTH

Regards

Inayath

**Plz dont forget to rate all usefull posts.

[Charger1129]

I don't have an IP helper currently set up but even when that is set up, how does the VLAN know which subnet (DHCP Scope) to use at that point? 

[fogemarttt · Accepted solution]

He will know it because of the subnet and the vlan. I have done it a lot of times and it is working fine. 

I suppose that, you have 3 floors and 3 different vlan. One subnet in each floor.

10.100.1.0/24 vlan 11   ip 10.100.1.1

10.100.2.0/24 vlan 12  ip 10.100.2.1

10.100.3.0/24 vlan 13 ip 10.100.3.1

i suppose the dhcp is 10.100.100.100.

on vlan 11 we will have,

interface vlan 11

ip address 10.100.1.1 255.255.255.0

ip helper-address 10.100.100.100

no shut

exit

on the 10.100.100.100 you have create the different dhcp scope for each vlan. 

when the dhcp will receive the request coming from 10.100.1.1 it will respond to this vlan by offering ip address coming from 10.100.1.0  network. 

If he receives a request coming from 10.100.2.1, he will respond with the 10.100.2.0 subnet. it is working like that. 

Hope it will help you.

Rate if useful and marked as correct to close this case. 

[paul driver]

HelloI

If you don't have the relaying already applied for the other dhcp scope then I guess you don't need it for this new vlan either.

I wouldn't  enabling relaying if you dont need to.

Check what device is performing the intervlan routing for you network. - basically your new L3 vlan will be configured the same way as the existing SVI's and also I  guess the dhcp server will be the same for the new scope ?

res

Paul

[fogemarttt]

On that vlan like vlan 20

you must do a ip helper-address @Ip of your windows server. 

I suppose that, you have create the dhcp scope in your server. make sure that you are not using cisco automacro on your switch interface. If it is the case, you have to remove the ip dhcp snooping rate command to be sure that you will get ip address on that interface. 

[paul driver]

Hello

1) Define a new ip subnet for vlan 20 and decided whets is to be the GW ip address for users in this vlan( this also will be L3 svi on the router/switch)
2) create the new dhcp scope on the dhcp server/router/switch ( if the dhcp server is remote then dhcp relay would be required on the L3 interface closest to the access switches

3)create the L3 svi interface for vlan 20 on the router/switch
4)create the L2 vlan 20 on vtp server in your vtp domain.( this should propergate through you vtp domain)

One all the above is in place and a client have been tested in the new vlan 20 and you happy to proceed. Arrange a change window and then just relocate the users access ports preferably when they have gone home, however for users still connected after hours another oiption is to decrase the dhcp lease time of vlan1 so that these suers will initate a new dhcp request after a short lease time.

res

Paul

[Charger1129]

Thanks for the help everyone! 

Another question to go along with this. If I was to create a new VLAN along with a dedicated subnet for the VLAN, how could I tell that VLAN to use that particular subnet from my Windows DHCP server? And NOT the default subnet I already have set up on that DHCP server? 

[Charger1129]

Thanks for the help everyone! 

Another question to go along with this. If I was to create a new VLAN along with a dedicated subnet for the VLAN, how could I tell that VLAN to use that particular subnet from my Windows DHCP server? And NOT the default subnet I already have set up on that DHCP server?