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I have two /16 networks which I want to divide : 10.84.0.0/16 and 10.94.0.0/16. I divided the first one in 4 equal subnets /18. But for the second I want a quarter of it in the first subnet, and all other IPs in a second subnet :

10.94.0.0/18  => 16382 IPs
10.94.64.0 ?? => all the remaining 49152 IPs

Is it possible ?

EDIT: to clarify, I have servers with databases. Each server has a primary IP address on interface eth0. Then on each servers I have several databases, each listening on there own IP address. I want to filter so that only secured workstations in a specific VLAN can access the main servers IP's (eth0) on port 22, and only applications in some VLANs can access databases IP's on DB ports (like 5432, 3306, 1521, etc.). So I have X IPs for servers, and a few times X IPs for databases. It's not a quarter, probably more like 5 to 10 databases per server. I could not find a solution by dividing a network, but I wondered if it was possible.

Jean Coiron
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1 Answers1

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Short answer: no, this is not possible from subnetting perspective. You can do /18, /18 and /17. /18 and "all the rest" is not possible.

Long answer: depending on your topology and goals it may be possible to use /18 and /16 range at the same time. E. g. you create one space as 10.94.0.0/18, and the second one as 10.94.0.0/16. Make sure that you actually allocate to 10.94.0.0/16 starting from 10.94.64.0. This way if packet comes to 10.94.0.0 - 10.94.63.255, it will be routed to 10.94.0.0/18 because this route is more specific. If packet comes to 10.94.64.0 - 10.94.255.255, it will be routed to 10.94.0.0/16. As long as real allocations (hosts, nested subnets, etc.) don't overlap, this will work just fine.

ar_
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