New VLAN/subnet

Tiras25 used Ask the Experts™
We ran out IP addresses on /24 so now the Data Center assigned us to new network /24 (256host). They want to make sure we are OK with that and no conflicts.
It sounds like a big change for me.  What should I be aware of.  What kind of things I need to take care?  
Please advise on the high level.
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
It depends what you are trying to do.

1. option: If both networks can be supernetted (joined) with mask /23, then you will just need to reconfigure network mask on current hosts from /24 to /23 and continue to add new host with addresses from new range with mask /23.

2. option: If networks can't be supernetted, then you will need to create new VLAN for new subnet, and check routing to verify all networks are visible to each other.

Please post your addresses so I can suggest you what to do.

From an OS perspective, I wouldn't be too concerned as long as there is correct routing. For Active Directory, make sure you configure your sites and subnets accordingly in Active Directory Sites and Services to ensure authentication and replication.
If you get addresses via DHCP then it all amounts to setting up the DHCP server with the new subnet information.  The computers will follow the server's lead, getting address leases from the server.

If you use static addresses then you manually enter static addresses, subnet mask, gateway and DNS server addresses in each computer/device.  These IP addresses should be OUTSIDE the DHCP range and not conflicting with each other.  Printers and servers are likely examples here as well as switches and routers which generally don't accept DHCP service.

That's it at a high level.

When you're done with all the address changes be patient.
Maybe even reboot all the computers .. like turn them off overnight.
Give them a chance to figure out who is who.
Don't expect My Network Places to populate very soon.
Learn Ruby Fundamentals

This course will introduce you to Ruby, as well as teach you about classes, methods, variables, data structures, loops, enumerable methods, and finishing touches.


Hi Fidelius, already made a decision with data center hosting to transfer over to the new network  /24. mask
 Now its /26 (typo in the question). mask


To answer other questions.  There are no DHCP.  All static servers, about 50 servers.
Thanks for the update!
So if you are migrating all of the servers to new /24  range all you have to do is change part of current addresses 10.1.29 to 10.1.109, and also change mask from to That is all for the servers.

You will also have to change IP addresses on your router and switches. Use same technique as I suggested for servers.

That should be it!

One more thing. If you will do it through RDP or other type of remote access be aware that you will lost conectivity as soon as you change IP address. So if possible do it from console or through ILO.



@motnahp00, my subnets is empty in AD sites and services.  So I guess one thing less to worry.
You should consider configuring these settings to avoid potential complications, especially with two subnets.


@Fidelius, would it be still possible to supernetted (joined) with another network?  What's the pros and cons there?  Hate to change all the IPs and what's not.
Pros and cons of wholesale migration vs. joining:

Wholesale migration:
- touches everything
- gets rid of *lots* of issues
- reduces complexity in the end
- requires less expertise
- provides a few less addresses

- may seem to reduce the up-front work
- adds up front work
- adds complexity
- requires more expertise
- provides a few more addresses

In cases like this I have written myself a step-by-step, site-specific procedure so that IP addresses are changed in some priority order with production machines having the highest priority and SNMP support kinds of things last.   Anything risky needs to be considered in making up the list.  Not only is this good planning discipline but it's a great guide for how you will proceed and a checklist.  And this gives you confidence that you won't "saw off the limb you're sitting on" if you are remoting in.
I might add:

If you are half-sure of what you're doing then you should have high confidence in wholesale migration.

If you are half-sure of what you're doing then that's perhaps not enough for joining.

So, I would want a compelling reason to join two subnets.

Best approach is likely to be:

Wholesale migration followed by gradual introduction of the old subnet if required.

But then, I'm assuming that you must change soon.  If not you could do the reverse.
Gradual introduction of the new subnet with low-risk machines on the new subnet first.

For supernetting two (or more networks), you need to have two networks with same subnet mask length and all networks must be covered with supernet mask.

For example:
- same mask length /24 and both are covered with supernet mask /23
can be supernetted as network: 192.168.0/23

On the other hand:
have same mask length of /24 but can't be covered with mask /23, so for these two network superneting is not possible.

More details here:

Now back to your situation. You hav existing network with mask /26 and new one with mask /24, and they are totaly different and so they can't be supernetted.

One thing you can do for easier transition is to create secondary network in same VLAN. I know for sure it is possible on Cisco devices, if you other vendor equipment, please post it so I can check.
Secondary network will allow you to have both networks operational at same time so transition will be very smoth. This scenario with two subnets in same VLAN can be used as long term solution also, but I don't recommend it, because it is very hard to troubleshoot things in setup like that. Use it only as temporary solution while you migrate your servers.

If you will go this route, post your network devices configs so I can help you in configurations (of course if your network equipment supports secondary network).



Thank you!  So this is what I did. Routed to the new network and then gradually put everything on new network and change the IPs.  Thanks all!

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial