segmentation

[jqadir]

Does any body know if there's an official size to when a flat network should be segmented?

i.e. If you have 100 IP address then you should be introducing routers…

Or does it solely depend on using network analysis tools to determine broadcast and collisions on the network.

[thisisshanky]

As long as you use a switch, each port is in its own collision domain. Now comes broadcasts. When the number of pc's in a segment increases, the number of broadcasts seen and processed by all of them also increases. Routers segment the networks into broadcast domains. Same is the case of vlan. A Vlan is one broadcast domain.

Segmentation of a network can be decided, based on a traffic analysis, how chatty the protocols being used are

[konigl]

And while there is no definitive rule as to how many devices a broadcast domain can support, the Cisco Press book "Top-Down Network Design" recommends (on page 103) the following maximum sizes based on desktop protocol(s) in use:

IP* - 500

NetWare - 300

AppleTalk - 200

NetBIOS - 200

Mixed - 200

*=If IP users are running multimedia applications with high-bandwidth and low-latency requirements, and/or a high level of broadcast or multicast packets, the maximum number of workstations should be reduced to 200.

Using that information as a guideline, if you set up your user VLANs so they each use an IP subnet mask of 255.255.255.0, or /24, you should be fine. This gives you 253 usable IP addresses plus one for the default gateway, per VLAN.