Should we go for /16 or /24 while designing the segment?

Castlewood used Ask the Experts™
We just acquired a new facility and are re-assigning a new IP segment for it. There are about 90 users and 120 computers/network devices in that facility.
Based on what we have now we would like to assign the segment My boss tends to use for it but instead of such a big segment I suggest using three smaller segments: for data for VPN for voip

Can you comment on the above two proposals and give your suggestion please? Thanks.
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Scott CSenior Engineer
I'd go with the 3 smaller segments.  One of our customers has a large segment and has some devices that are killing network performance for everyone.

If the devices were on their own segment, I feel that the entire network would not have been impacted.
Ken BooneNetwork Consultant
Definitely 3 /24 segments.  For a myriad of reasons.

It is a whole lot quicker to scan a /24 than a /16 if you are looking for something.
You mentioned voice.  Best practice is to ALWAYS have voice on its own network segment.
Management - Much easier to identify what traffic is what when they are broken out.  
Security - You can put ACLs on the vlans to limit traffic flows between vlans if you need to.
With that amount of devices, I think that /16 is overkill. 3 smaller subnets is MORE than adequate. What I might be tempted to do if it were me though, is create the subnets as:- - DATA - VPN - VOIP

That way, if ever you want to expand your data scope, you could re-subnet as:- - that way you would have DATA addresses from - and wouldn't have to worry about re-subnetting VPN or VOIP
I will give my take too.  /16 is overkill, however, if you have multiple facilities I recommend a /16 for site.  This will make the route tables smaller for remote sites connecting, they know that is new facility.

Then in the new facility use 3 subnets,,, ect......   You can add more subnets in the future with ease,
Similar to Bryant's comment, if you decide on three /24 subnets, then I'd suggest a /22 for the whole site, which you can break up into four /24 subnets.  Then you only have one routing table entry for the whole site.

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