DHCP Scope

Dr Zoidberg · 7 Oct 2008 at 12:58

I am running out of IP address in the current scope and am looking for some confirmation on what i can / cannt do to add more.

If for example our current scope is 192.168.10.XX
With the start IP at 192.168.10.21 and the end IP at 192.168.10.199

Can i change the start IP to 192.168.9.1 so the pool covers the range 192.168.9.1 to 192.168.10.199 ?

We have 1 subnet set up and i understand you can only have 1 scope per subnet?
That is why i would prefer to enlarge our current scope, rather than add a 2nd subnet.

Thanks
Keith

wij · 7 Oct 2008 at 13:05

If your hardware supports it a class b subnet may be an easy option.

WILD9 · 7 Oct 2008 at 13:14

as wij mentioned a class b subnet is what your after, 65534 addresses should last you a while

. Im assuming (by your example of a 192 address) your running NAT rather than just allocating from a range supplied by your ISP.

If your in doubt a class b would give you : 192.168.xxx.xxx with a subnet of 255.255.0.0

bigredshark · 7 Oct 2008 at 13:23

WILD9 said:
as wij mentioned a class b subnet is what your after, 65534 addresses should last you a while . Im assuming (by your example of a 192 address) your running NAT rather than just allocating from a range supplied by your ISP.

If your in doubt a class b would give you : 192.168.xxx.xxx with a subnet of 255.255.0.0

Though arguably you should never have a scope that big, it's just bad design.

wij · 7 Oct 2008 at 13:30

Indeed, using a 20bit subnet still gives you over 4000 hosts and 16 subnets. (Is that still bad design, works well for me

)

bigredshark · 7 Oct 2008 at 13:39

wij said:
Indeed, using a 20bit subnet still gives you over 4000 hosts and 16 subnets. (Is that still bad design, works well for me )

I don't think I'd ever create a scope larger than a /23, maybe a /22, anything else gives you huge broadcast domains and shouldn't be necessary in a well designed network. Ideally I stick to /24s for client access.

WILD9 · 7 Oct 2008 at 13:52

bigredshark said:
Though arguably you should never have a scope that big, it's just bad design.

Yes, obviously scale it as you need more addresses, dont just jump from 254 to 65000 odd

Dr Zoidberg · 7 Oct 2008 at 13:53

Thanks i think you are right, done a little more reading into it.

I think it is going to be a major job to change, once i confirm the hardware is up to it,
Currently we start with 192. which cant be used in a class B subnet ? so all our 'static' IP will need changing, and then im sure there will be issues to sort out with lotus notes etc etc.

I just need to add a 2nd range at the 3rd octet as noted in my first post.

But first we have to check other group sites are not using a range we want to move into.

I want to have a clear idea of what needs to be done and how we are going to do it before i go higher with it.

Looks like i have some more reading to do and a lot of work ahead.

bigredshark · 7 Oct 2008 at 13:57

I strongly suggest you don't just change your entire network to a class B, putting more than 250 odd devices in a broadcast domain is a BAD idea for scalability and performance. If you really need more than 254 addresses for your kit, I'd start deviding your network up properly, set up a second class C for servers, maybe use mutliple class C ranges for client machines in different operational areas or geographic locations. Just expanding it to a class B is very very bad practice though.

Dr Zoidberg · 7 Oct 2008 at 15:24

bigredshark said:
I strongly suggest you don't just change your entire network to a class B, putting more than 250 odd devices in a broadcast domain is a BAD idea for scalability and performance. If you really need more than 254 addresses for your kit, I'd start deviding your network up properly, set up a second class C for servers, maybe use mutliple class C ranges for client machines in different operational areas or geographic locations. Just expanding it to a class B is very very bad practice though.

I agree with you after doing som emore google seaching and reading,

For now we are going to try a short term fix and expand our current scope which only goes to .199
There are devices above this but scattered around all over the place, they can be re-configured towards the top end and then we should be able to add around 30 more IP to the current scope as soon as i find out if it is possible to alter an existing scope.

But long term we will still need to look at expanding and will look into a 2nd Class C subnet,
The extra 30 IP we can get now will only cover devices that are on or going to be placed on order at the moment so no long term room left.

Tui · 7 Oct 2008 at 17:31

If you're looking at increasing the current scope, you can add the 192.168.11.X range if available. The network will be 192.168.10.0/23, usable range 192.168.10.1 - 192.168.11.254

You'll need to change the mask of all your fixed IP devices (router, servers etc) and what DHCP hands out to 255.255.254.0

In a Windows environment, you should exclude from being used what would be a class C network or broadcast address, in this case 192.168.10.255 and 192.168.11.1
Increase the allocated range as required.