How to change from CLASS-C to CLASS-B IP Schedule

Posted on 2009-04-03
Last Modified: 2012-05-06

Currently our Network is on Class-C network segment but it was poorly configured to ALL static ip addresses and NO DHCP at all.  Now our network has extended so far that very soon we'll run out of IP addresses.   I don't have a lot IP management background as it relates to switches and routers, but DHCP configuration that I can do.  Now, the BIG Question is???? what's the process of switching from a CLASS-C to a CLASS-B network segment?   Do we need to hire an expert to do this or it's something I can setup a DHCP and point all the servers, NATed devices, workstations to it?   We've a very complicated network.......our systems talk to other systems around the country 24/7 and all the mission critical applications MUST be ONLINE at ALL Times.
If I need to explain further, please let me know.

Question by:timnjohnson
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Expert Comment

ID: 24061268
Are you using public or private IP space?
If you are using private IPs you can just bump your mask one bit to the left and double your IP space. Once you go over 500 addresses though you should think about going with multiple subnets.
If you are using public space it get a lot more complicated. You would need to get another network from ARIN.

Author Comment

ID: 24061354

We're using Private 192.168.x.x but it also connects to other NATed devices on the Public space.
Using 192.168.1. 1 -as our gateway, how can you double that...give me a little 102 guide.  


Expert Comment

ID: 24062141
So right now you are using a mask, correct.
If you change your mask to your usable range will be 192.168.1-2.x
Just change the mask on all your clients and begin using the additional space no further changes would be required.
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Expert Comment

ID: 24062167
Your usable rage will be 192.168.0-1.x
You still will not need to make other changes.

Author Comment

ID: 24071536

I think our biggest problem is how to go about notifying other parties and locating devices that are still pointing to the old address.    It's a very scary thing to do on a live production network and because no one the tech team is well equipped to handle this kind of infrastructure change, I think a qualified contractor is best suited for this.   Does anybody else think otherwise?  Let me hear your opinion, I need to meet with our IT manager who has no IT technical background at all, and give him my suggestions.    We run a 24/7 operations center and anything we do, will affecting more people and has a potential of shutdown our network for days if not weeks.  Is there a workaround? Can add to what we have without interrupting or touching our current IP configuration?   A lot of questions to............

Accepted Solution

Sniper98G earned 500 total points
ID: 24071957
None of your old addresses should change if you just alter your subnet mask. Your current space will be left entirely intact and you will simply have additional addresses. If you have firewalls, ACLs or firewall holes along the way they will also need to have their subnet/wildcard masks changed. But; once you pass the device that does your NAT noone will even know the differance.

Author Closing Comment

ID: 31566288
seems that the answer may not be straight forward but will do more research to come up with complete solution.  

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