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How to segment a /16 network?

Hi Experts,


My boss told me that they were on a /16 network before yet they are segmented. How did they do that? Is it even possible as I imagine all of their network devices will be on a single broadcast domain? This is possbile for statically assigning IPs but how about with DHCP involved? Im really puzzled or confused. Any idea how they did that?


Thank you so much in advanced!



Georg Pauwen
VIP Expert



I am not really clear on what you are asking. A /16 network has 65534 host addresses, so even if you use smaller subnets derived from that range, you can still be all on the same broadcast segment...

Hi George,

Yes, I understand that that will be the case. Apologies for the confusion but what I would like to know is how they did the segmentation with DHCP servers involved as I dont think they will assign static IP addresses to their devices all through out. Any thoughts?


Joseph W. Doherty
Hall of Fame Expert

Much depends on what your boss means by segmented.

Yes, it's possible a single /16 is one broadcast domain. How well it would work would depend much on the volume of broadcast traffic, which often ties into how many hosts are actually active within the /16.

As to unicast traffic, it might be "segmented" by using bridges, the most common of these would be L2 switch, which is also a multi-port bridge.

Hi Joseph,

Please excuse my ignorance as I just started learning Cisco. Can you explain more how an L2 switch can help with the segmentation? Also, how do you think they did the DHCP IP assignment between network segments? Im pretty sure they wont do it statically throughout all their devices. Can an L2 switch be configured as the DHCP server for each network segment? Or it can only do IP Helper from a DHCP server?

Thank You!


Depends on what you mean by "segmentation". I recall it meant, in fact, segmenting a L2 media using bridges, this to limit unicast from flowing out of the bounds of a segment if the destination MAC was within that segment. Again, as a L2 switch is a multi-port bridge, it does this too, and I recall switches were also known to "micro-segment", since individual hosts were often connected to single ports. BTW, L2 segmentation, also limited the L2 half duplex collision domain and further allowed extension of segments beyond the limitations imposed Ethernet timing requirements.

As far as DHCP is concerned, logically the forgoing segments are still on the same logical wire. (Remember, broadcasts will span bridge segments, as will MACs not on the local segment.)