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Subnet help

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Last Modified: 2020-01-16
Hi,

I've been given the below from my network team.

192.168.10.0/20 – they've asked me to subnet accordingly and re-address your VLANs with.

Can someone advise what is required

Thanks in advance
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Fred MarshallPrincipal
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Commented:
First of all, 192.168.10.0/20 resolves out to 192.168.0.1 to 192.168.15.254 (4094 addresses)
And, just for fun, 192.168.10.0/23 resolves out to 192.168.10.1 to 192.168.11.254 just in case that's what they meant. (512 addresses).

"To subnet accordingly" must mean to break it up into suitable subnets for your situation.
To "readdress your VLANs with" must mean to assign various of those subnets to existing VLANs.

What is required:
First, confirm that the address specification is what was intended because 192.168.10.0 is in the MIDDLE of a /20 range.  So, that's an odd way of putting it and does need to be checked out.

/20 has 16 /24 subnets.  /24 is pretty common.  So, if you stick with /24 subnets, you have room for 16 of them.
If 16 is too many then consider 8 /23 subnets of 512 each,  or 4 /22 subnets of 1024 each.
Some will tell you that this is starting to get a bit big but modern switches make that less likely a problem.
And, you can split 4096 up into odd sizes like:
1024, 512, 512, 256, 256, 256, 256.  But I'd NOT do this unless absolutely necessary.  Having them all the same size with the same subnet mask is less troublesome.
A good rule of thumb is to provide plenty of extra space relative to your immediate needs.  A factor of 2 isn't too much.
So, if you need 256 hosts, set the subnet size at 512.
As the subnet gets larger, you may taper off on the margin you provide - just think *absolute* numbers instead of percentages / factors.
This is excellent thank you!
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