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/24 network running out of free IP addresses

Posted on 2014-02-09
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Last Modified: 2014-02-12
Hi Experts,

Our 192.168.0.0 /24 network is running out of IP addresses.

What's the easiest way to get more addresses without changing the whole class (to 10.0.0.0 /8 or similar).

Can I just change the network mask on all devices and servers to /22?
That seems like the easiest way to go, I just wonder if that will work.

Please notice that we have a SAN network on 192.168.100.0 /24 - I want to make sure it won't be affected.

Let me know what you think.
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Question by:itorana
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by:computication
computication earned 250 total points
ID: 39846443
The easiest way to go is to change your network to a /23. Or /22 if you feel, you need the extra IP addresses. This will not interfere with your SAN.

You could also go for VLAN separation but that requires more work and layer 3 switches.

Kind regards,

M
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by:Surrano
ID: 39846670
With these restrictions you can go as high as /18 (192.168.0.0-63.255) but I'd say that there must be something strange in your network topology. Slicing into smaller subnets would likely improve routing performance as well, even if you need to add another router.

Try to reorganise the IP addresses into subnets of <256 by means of
- physical topology (e.g. server room A = 1.0/24, server room B = 2.0/24
- logical topology (e.g. finance = 1.0/24, production = 2.0/24, development = 3.0/24)
and have common networking like the main route towards the external world is 0.0/24

Even if you have some (or even hundreds of) virtual interfaces on same piece of cable you could easily achieve different subnets used by different virtual interfaces on same physical interface. E.g. if you have a virtualisation server with 200 vms and 5 virtual interfaces each (o&m, app, db, cluster interconnect, backup) then you can configure the 200 O&M interfaces to use 1.0/24, the 200 app interfaces to use 2.0/24 etc.

Just make sure that the routers they are connected to also receive messages on all of these subnets.
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Author Comment

by:itorana
ID: 39846677
Hi Surrano,

Thanks for detailed reply! We don't have any routers or even layer 3 switches to do routing. Could that cause problems in the future if we just changed the mask to /23? (500 addresses is more than enough).
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Expert Comment

by:pergr
ID: 39846726
I recommend changing to /23.
You will keep using the same default gateway as before.

Generally, just change the /23 in your DHCP settings, and do not worry too much about migration. Catch up with all statically configured devices afterwards.
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Surrano earned 250 total points
ID: 39846761
subnets should work with plain old "dumb" hubs or switches as well. Those that are so dumb that they don't know anything about netmasks :)

as a gradual approach, if you change the netmask to /23 or even wider then you can proactively distribute the static IP addresses and define the dynamic ranges in a way that later on, if you think it's worth the effort, you can change from one wide netmask to several narrower ones. But the simplest solution for the time being is indeed to simply change the netmask but make sure you do it everywhere.
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by:Soulja
ID: 39847434
What type of device is providing the routing for your network? You can just go to that interface and configure a secondary subnet on it.  This way you don't have to make any changes to your existing devices.
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