Broadband install: need to change IP ranges

[Asreal]

Okay guys, newbie question for the geniuses:

 

Situation:

New broadband installation is imminent, only I have been told that because our new firewall & filtering is hosted externally (by new ISP) I am going to have change our entire network address range so that it doesn't conflict with another schools network.

(Never thought this would be a problem being a private range, how wrong I was...)

 

Question:

For someone who's never done anything like this before, what's the best way of going about making all of these changes?

Are there any things I need to really watch out for?

 

Any advice anyone could give would be much appreciated!

[Michael]

The biggest headache will be to do it in the correct order, but realistically out of hours is best.

 

Change your server static IP configuration first, then DHCP, and then printers and any admin workstations with a static configuration.

[djm968]

I would install a NAT box and use your own private IP range for your LAN this will only be a little bit more work and you will never have this issue again if your ISP changes the IP range/

[Arcath]

I did this not that long ago for one of my schools (went from a /24 to a /22) and it wasnt that bad.

 

My process was:

 

1. Statically set a laptop my current range and run Angry IP Scanner on the current range (just to get everything)
   
2. Change the servers IPs to the new range
   
3. Change the DHCP scope to the new range
   
4. Change any reservations
   
5. Turn the switches off/on again (This causes a re-lease on every device)
   
6. Re Run the IP Scan
   
7. Change the important devices in the left overs list first
   
8. Change the IP Printer ports on the print server
   
9. Re Run the IP Scan
   
10. Plod through the remaining devices and change them
    
11. Repeat Steps 9 & 10 until the IP Scan returns only the laptop you set statically
    

 

 

In all it took me not much more than on hour to do, most things had a reservation so it was nice and easy.

Edited March 10, 2014 by Arcath
List syntax was wrong

[pete]

Ensure any IP-based ACLs are updated before swapping the ranges.

[fairm010]

I did this not that long ago for one of my schools (went from a /24 to a /22) and it wasnt that bad.

 

My process was:

 

1. Statically set a laptop my current range and run Angry IP Scanner on the current range (just to get everything)
   
2. Change the servers IPs to the new range
   
3. Change the DHCP scope to the new range
   
4. Change any reservations
   
5. Turn the switches off/on again (This causes a re-lease on every device)
   
6. Re Run the IP Scan
   
7. Change the important devices in the left overs list first
   
8. Change the IP Printer ports on the print server
   
9. Re Run the IP Scan
   
10. Plod through the remaining devices and change them
    
11. Repeat Steps 9 & 10 until the IP Scan returns only the laptop you set statically
    

 

 

In all it took me not much more than on hour to do, most things had a reservation so it was nice and easy.

 

I'll be doing this soon, cheers for the list. Does this have any adverse effect on DNS?

[Michael]

I'll be doing this soon, cheers for the list. Does this have any adverse effect on DNS?

 

Yes - that's why it's crucial to switch all servers first. Everything in your network relies on DNS. If it fails or it's not working, you will notice problems.

 

When changing the IP config, it's important to re-register with DNS manually to speed up the process (via the command prompt). This will then replicate through to other DNS servers on your network.

[fairm010]

So any clients picking up an IP on the new range will register in DNS ok, providing the servers are all ok first? Also will I have to change my subnet mask?

[Michael]

So any clients picking up an IP on the new range will register in DNS ok, providing the servers are all ok first? Also will I have to change my subnet mask?

 

Correct and possibly. When you're given a new range to play with, all details will be provided. Of course the other crucial part of DNS is your Forwarders. Most LAs setup their own, however you have a choice between the new nameservers at your ISP, or alternatively Google DNS or Open DNS which are generally pretty reliable.

[Arcath]

Yeah my issues in the week or so afterwards where all down to devices using ip addresses in paths etc... but it didn't cause any major disruption.

 

I actually ended doing it twice at one site in less than a month. Our LEA didn't record that we had been given a new range and gave it to someone else, then when we did swap to it (after sitting on the job for 6 months) we had a painful connection with things just not working. I was no impressed when the LEA said I had to change it all again.

[fairm010]

We've just had our lovely new boradband installed but i've noticed recently we are low on IP's and ideally I want to separate out server and printer ranges. We are currently running on the old LA provided range (255.255.255.0) but can move onto a new one now.

 

Just realised I've hijacked the thread, perhaps I should go start my own! Apologies OP

[Asreal]

NP! You're asking thing's I've missed

(Plus, I'm glad it's not just me!)

[Michael]

Yeah my issues in the week or so afterwards where all down to devices using ip addresses in paths etc... but it didn't cause any major disruption.

 

I actually ended doing it twice at one site in less than a month. Our LEA didn't record that we had been given a new range and gave it to someone else, then when we did swap to it (after sitting on the job for 6 months) we had a painful connection with things just not working. I was no impressed when the LEA said I had to change it all again.

 

Sounds as though it was a bit poorly managed and I agree - not good changing twice in a short period! Again the slowness can be caused by DNS. If we didn't have DNS we'd have to remember incredibly long strings of numbers!

 

I've said to a lot of teachers - Can you remember all the names in your class? 'Yes' - Can you remember all their phone numbers? 'No' - that's what DNS is for

[Asreal]

Thanks btw folks; has been a great help!

 

Rumour has it that some of our extreme switches have had their IPs configured manually - anyone had to do this very much?

[Michael]

We've just had our lovely new boradband installed but i've noticed recently we are low on IP's and ideally I want to separate out server and printer ranges. We are currently running on the old LA provided range (255.255.255.0) but can move onto a new one now.

 

Just realised I've hijacked the thread, perhaps I should go start my own! Apologies OP

 

A subnet of 255.255.255.0 will be a Class C network, giving you 254 IPs. Depending on the size of your school, it most likely isn't enough. You have to take into account many users connect their Smartphones to the WiFi too and it soon adds up!

 

Try reducing the lease time down to 3 days in DHCP Server, so it frees up more IPs in a shorter period of time.

[fairm010]

Yeah thats it! We are nearly at capacity as is but we are due to extend soon. The lease time is currently at 24 hours.

[Michael]

This great tool allows you to calculate an appropriate IP range

 

From what you're saying, either 510 or 1022 hosts/unique IPs would be more appropriate than the max 254 on Class C. You can then relax DHCP and set it to 3 days or more.

[fairm010]

Thanks Michael, that helps a lot!

[Snuffkins]

Thanks btw folks; has been a great help!

 

Rumour has it that some of our extreme switches have had their IPs configured manually - anyone had to do this very much?

 

I'm assume you know the IP address of your switches to Telnet onto them? Alternatively you'd need a serial cable for the console. Either way login and "show vlan". That'll show you all of the vlans and what IPs are configured for them. If your network is flat, this will be easier for you as you'll only need to change the one address. If you have multiple vlans listed with IP addresses then you've got a little more work to do and it won't be as simple as just changing an IP address.

 

 

To change the address it would be "Configure 'VLAN_NAME' ip address 'NEW_IP_ADDRESS'

[IrritableTech]

I'd change your ranges as suggested by your ISP. Adding another NAT device in the mix is asking for headaches. Double NATing isn't going to be fun.

 

We changed our range a couple of years ago to expand our LEA supplied subnet. I was quite nervous about it, but actually it wasn't too difficult.

 

I changed the IPs on the servers but placed the old IP address in as an alternative. That way I could create and configure ranges (in DNS, dhcp etc.) before the switch over day.

 

One important thing to remember I haven't seen mentioned is to add your new range to the sites and subnets area of active directory.

 

After you've switched over try to periodically sniff the packets on your network (I use wireshark). You can then identify the devices you missed in your planning. It's amazing where software/hardware/profiles etc. hide these settings. Then once you're confident you've found everything, you can delete the old - alternative - IP address from your servers.

[Marshall_IT]

All I'd add to this is if you have got multiple VLANs you'll need to look at your core switch and the routing /ip helpers.

 

Other than that everything is covered here already.