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Windows Thread, Help in changing live DHCP Scope in Technical; We currently have a DHCP scope of 1024 address’s but this range is now nearing its functionality as we soon ...
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    tosca925's Avatar
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    Help in changing live DHCP Scope

    We currently have a DHCP scope of 1024 address’s but this range is now nearing its functionality as we soon be adding 200 clients on the network and our range will not cope. So, I need to either change the DHCP scope all together or super-scope. I am thinking of completely setting up a new range that is on private address’s. WE currently have our range supplied by the LEA and all schools are on a WAN. All secondary schools have 1024 ip allocated but most are no where near using them.

    The range currently in use is 172.18.244.* to 172.18.247.*. I am going to go over to 10.10.10.1 to 10.10.20.1. What is the best way to do this? Can it be done live or do I need all the clients off etc.

    Could someone give me advice on how I should plan this and best case options? I also intend to set a new ISA box up that will act as the Gateway to all clients.

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    Re: Help in changing live DHCP Scope

    Hi,

    What i would do is decrease the lease time on the existing scope to say 1 hour and then do deploy a startup script that will release and renew the ip address on the fly. The purpose of doing this is all the clients will then need to renew the IP address as it will be within their 50% of the lease time so when you setup a new scope and activate it the clients will try to get the IP address from the new scope(s).

    Otherwise what you may find is that client sticks to their old IP address because of the lease period is not within the 50% when they usually try to renew it.

    I woudl create the new scope and set all the options up but don't activate it. When all the clients are booted up and the start-up script has run, deactivate the old scope and activate the new scope.

    There might be more eligant ways of doing it but this has worked for us. Also you may find that some clients will stick to their IP even after renewal, if this is the case set that client on any static IP address and commit it and then set it back to obtain ip from DHCP and it should pick up the ip address from the correct scope.


    HTH,

    Ash.

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    Re: Help in changing live DHCP Scope

    We have just done this during half term for exactly the same reasons - used up our 1024. This was particularly bad when we were setting up new kit while the old kit was still in place so doubling up on the addresses (plus when we were setting up wireless laptops with a hardwire they were obvisouly grabbing two leases - one for each nic)

    After looking at all the options we (us and the LEA together) decided the best way forward was to extend the LEA scope.

    This was pretty painless - especially during the holiday - It actually only took us half an hour or so - not including re-assiging all the ports on the print queues.

    This was all we had to do was update anything static (servers) and then set up the new scope on the DHCP server.

    It is worth cutting down the length of your DHCP lease on the "soon to be extinct" scope a few days before the change over to a very short period of time (a couple of hours) this way the clients will be looking for an address much more frequently - i.e. if you set it to two hours then the longest it will take a client to pick up an address from the new scope is two hours because it will pick up a new one as soon as its lease runs out. The Clients will be out of action if they have an old IP address after the change has been made.

    We had a few months to plan for ours and over that time made sure as much kit as possible was using DHCP for its IP address rather than static - this meant that we did not have to visit any of it to get it onto the new scope. We can now go back at our leisure and make any static that we want to.

    A few machines needed a DNS flush (ipconfig /flushdns) to address a few issues so we put this command into the login script for a couple of days to make sure it was done easily globally.

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    Re: Help in changing live DHCP Scope

    What considerations do i need to take into account for DNS?

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    Re: Help in changing live DHCP Scope

    I've just done this.
    The clients on dhcp should just pickup the new ip address. Dns will update on its own. The only main problem I had was with print servers. I had to go around and reconfigure them. They were on static but now they work on dhcp with resevered addresses.

    Have you looked at subnetting/vlaning your network off? You broadcast domain will be getting a bit big with all them clients.

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    Re: Help in changing live DHCP Scope

    I've done this as well, I just increased the subnet to 255.255.252.0 on dhcp and all machines. Took less than 30 minutes to do. Worst thing was changing the networked printers via their web interfaces.

    We don't have any LEA involvement in our internal ip range. Just out of interest why would they be involved?

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    Re: Help in changing live DHCP Scope

    Quote Originally Posted by ittech
    We don't have any LEA involvement in our internal ip range. Just out of interest why would they be involved?
    Presumably if they are acting as the ISP for local schools

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    Re: Help in changing live DHCP Scope

    Quote Originally Posted by NetworkGeezer
    Quote Originally Posted by ittech
    We don't have any LEA involvement in our internal ip range. Just out of interest why would they be involved?
    Presumably if they are acting as the ISP for local schools
    RM dictate our IP range and I still don't know why exactly. I assume it's so they can snoop on us if they want. Internet is the only thing we use from RM (apart from SuccessMaker) and that's only because our LEA forces it upon us.

    It took over a month to get a new range organised when we wanted to go from 1024 to 2048 addresses! We had to use an entirely different range when in theory, if they didn't have control over it, we could have just changed the subnet to 255.255.248.0 etc.

    We had two ranges before we merged networks (one for admin and one for curriculum) and it was a nightmare getting all of our open ports changed to the new range since we had to put in a request for each one and then wait weeks for them to get changed. We also had to make sure that the old ranges and port forwarding were still functional until we joined the networks.

    HBJB

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    Re: Help in changing live DHCP Scope

    [quote="Ittech"[I've done this as well, I just increased the subnet to 255.255.252.0 on dhcp and all machines. Took less than 30 minutes to do. Worst thing was changing the networked printers via their web interfaces.

    We don't have any LEA involvement in our internal ip range. Just out of interest why would they be involved?[/quote]

    in our case (and in many other LEA's) our network is a subnet of their network.

    If we just changed the network mask then there would be all sorts of problems because the extended subnet would be duplicating the IP Addresses of other PC's in the LEA.

    It is not like a normal ISP where they give you perhaps one static IP address for your entry point and then from there you control it (although we could if we wanted to probably). They control our router and therefore our subnet information and our default gateway.

    Makes things like remote support and video conferencing easier for them and us to make happen and it is only really a problem when you want to change something like in this instance.

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