Superscoping 1

[lbarron]

Hi,

Does anyone have any experience of superscoping?

We have a single subnet 192.168.0.x and are fast running out of capacity. All our IP's are static at the moment.

If we were to setup DHCP and setup a superscope we could effectively setup another scope and bind them together?

If we did this would we keep the single default gateway and use the same dns server?

Or is there some other configurastion that would need to be done?

Thanks

Lee

 

[burtsbees]

You could bind 192.168.0.0 and 192.168.1.0 together with a /23 (255.255.254.0), if that's what you mean...

Burt

 

[VinceWhirlwind]

Reducing the size of your subnet mask by one bit will double the number of addresses available to that subnet.

On the other hand, it might be nice to keep with the /24 subnet and create a new /24 subnet if it is on a physically separate switch.

This keeps the size of your broadcast domain down.

Also, it means you can look at an IP address and say:
"192.168.1.42 - that one must be in Building B".

 

[burtsbees]

Vince---I think the user wants to create two separate subnets, but supernet them for DHCP only. At least that is my take on it...

Burt

 

[sixteamparlay]

You'll need a DHCP server on the second subnet, or a DHCP Relay agent pointing to the main DHCP server.

If a relay is used then the main DHCP server needs a new subnet allocation range for the new subnet.

 

[VinceWhirlwind]

Lol!

I should have googled "Superscoping" first.

I just googled for it then and found this:

http://support.microsoft.com/kb/186341

Maybe that article is very old or something:

"Supernetting is used when multiple, consecutive network addresses of the same Class are combined into blocks. For example, if you need to assign 199.1.1.x and 199.1.2.x to the same physical network and want to change subnet mask. You would use the subnet mask of 255.255.254.0..."

Wrong! (Unless you use Jurassic-era network devices).

The answer to the original question is "Don't do it".
I read

http://support.microsoft.com/kb/161571/EN-US/

and "multiple logical subnets on one physical network" is not good practice.

Keep things simple.

 

[burtsbees]

Again---only for DHCP so the server can hand out dhcp to both subnets without a relay agent! The user HAS 2 separate subnets!
Look at it like actual supernetting---a router running EIGRP can summarize networks as a supernet to reduce the routing table size...there are still separate networks!

Burt

 

[VinceWhirlwind]

I don't get you.
He said "If we did this would we keep the single default gateway and use the same dns server?"
At that point, he's thinking of Supernetting not Superscoping.
And from reading the MS KB articles, Superscoping seems to insist on "multiple logical subnets on one physical network", which he should not introduce to his network design which currently is a single subnet.
The easiest would be for him to simply follow your first suggestion.

 

[burtsbees]

I read it like he wants to set up another scope (but meant subnet) and bind them together for DHCP.
I did not address the issue of the same gateway---I wanted him to clarify what I thought he was saying first. If he confirmed what I thought, then I actually would have suggested VLANs in layer 3 switches, since the gateway thing would fit that scenario. But then if he would say "we only have L2 switches", I would assume at least five 48-port switches and one 24-port switch, if an entire subnet was almost out. See where I'm going with this? I just needed additional info from him, and sometimes I derive this info in offbase ways, I admit...

Burt

 

[burtsbees]

Crap---my 4 year old hit "post" before I proof-read that...hope you understand what I'm saying...

Burt

 

[VinceWhirlwind]

Yes, I know what you mean. An idea of his physical topology would help. And switch models.

But basically, to have the same default GW for old & new devices, follow Burtsbees initial suggestion of creating a DHCP scope with 192.168.0.0/23.

You should reconfigure all your static devices' IP options to make them DHCP as well. Otherwise, connectivity between new and old devices will be either odd or broken.

If you want to learn about VLANs, let us know and we can explain something completely different.

 

[sixteamparlay]

most newer switches have the ability to act as the DHCP relay agent so take advantage of it. Set the switch to relay to your main DHCP server

 

[Torturednacho]

router on a stick