Supernetting...

[Bubbagump210]

I have been given the task of expanding our /24 network to a /22.The network is currently 192.168.15.0/24. 192.168.2-30 are reserved for static IPs, the rest are fair game in DHCP. here's the rub so far as I understand... the third octet must be divisible by 4 to get to a /22. Is that correct? If so, I am sort of screwed as I will have to go to 192.168.12.0/22 to try to maintain some continuity. So what is the easy way out of this as?

My thinking... set the DHCP leases to like an 1 hour expiration and wait for things to cycle once (currently it is 7 days I think... Microsoft default). On the router change the default gateway subnet mask to 255.255.252.0 but leave the IP as is. Update routes to reflect the new super net. Change the existing static IP hosts to the new subnet mask leaving IPs alone. Wait a day and be sure all DHCP leases have cycled. Change the DHCP scope to 192.168.12.0 with a subnet mask of 255.255.252.0. Profit??? Does this sound right or am I out of order somewhere?

 

[lif_andi]

You mean that 192.168.15.2-30 are reserved right ?

First of all, from the network perspective, expanding the subnet to a /22 is not recommended. It would be better to use VLANs. Whether that is the recommended course for you depends on the size and budget of your firm.

That out of the way, you're thinking it alright. Its not a best practice network, in case of a failure it might cause a lot of grief, but what you are thinking will work.

Be aware though that if you have 150-200 hosts or more, things might get crowded on the wire, and if there is a NIC failure or some such, it can cause a lot of problems.
If your network is 10/100 (Mbps) recommend to your bosses to invest in a L3 switch and a capable person to set it up. It will save money in the long run.

 

[imagoon]

Yes x.x.15.x would be in x.x.12.x.

Also /22 works just fine as long as your network is configured for it. I have several /22 in my 65+ site environment. Honestly I wouldn't be all that concerned with lif andi's concerns. Most of our /22 networks have 400-500 hosts on the system. Everything from desktops to cell phones. From my experience /22 is the commonly accepted max currently.

I have seen a couple of people try and say "Windows can't handle /22" or "Linux is fine with even larger" or other random generalities that don't often seem found in fact.

 

[Mir96TA]

It will work. But why ? its your Lan Design it better.
(L3) Core Switch => (L3) distribution => (L2) Access Switch
or
Core Switch (L3) => Access Switch (L2) (Vlan)
BTW SuperNeting SUCKS

 

[Railgun]

It will work. But why ? its your Lan Design it better.

It has nothing to do with designing it "better." It's about the environment it supports, scalability, and a whole lot of other things that you can't possibly know about to suggest "design it better."

I too have retrofitted a few /24s into /22s. Not an issue at all.

BTW SuperNeting SUCKS

So design it correctly.

 

[Genx87]

Why does Supernetting suck?

 

[imagoon]

Could go even as far as "what is supernetting" because it is a concept only related to classful networking which really hasn't been used in decades.

 

[Genx87]

I am a little confused by your current setup. When you say "192.168.2-30 are reserved for static" do you really mean 192.168.15.2-30?

If that is the case. You can certainly leave those static IP's, but change the subnet to /22 on those devices.
In your new DHCP scope exclude 192.168.15.2-30 from its range.

And yes you will be running a 192.168.12.0-192.168.15.255 range.
You are on the right path for how to handle the switchover by dropping lease times to 1 hour. This will get the clients to renew within 30 minutes.

 

[Mir96TA]

It has nothing to do with designing it "better." It's about the environment it supports, scalability, and a whole lot of other things that you can't possibly know about to suggest "design it better."

I too have retrofitted a few /24s into /22s. Not an issue at all.



So design it correctly.

I have subneted /20 to /26 and it worked and perform lot better

 

[Mir96TA]

Why does Supernetting suck?

Cause its lot of broadcast and network comtablity to apps issues.
That is why we going to words ipv6

 

[Genx87]

ipv6 will solve app compatibility?

I haven't had any issues using supernetting nor have I heard of anybody else having issues who has done the same. Of course that doesn't mean there aren't issues. But what issues have you run across when implementing supernetting?

 

[xSauronx]

Could go even as far as "what is supernetting" because it is a concept only related to classful networking which really hasn't been used in decades.

i blame education for still teaching subnet classes and classful routing. or at least, they were teaching 6 years ago when i was in school.

when that is the first part of it you are taught, its hard not to think of subnets in those terms

 

[Mir96TA]

ipv6 will solve app compatibility?

How did you come to think like that?
iPv6 will slove lot iP4 problem like subneting and
Reason we do subnet aka broadcast