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Subnetting scheme for 3550 L3 in the wiring closet

We have a C6000 backbone to aggregate 16 wiring closets containing clustered C3550s. I plan to use the C3550 L3 for inter-VLAN routing only. Does anybody have a good addressing scheme? One subnet per switch? How do you handle spanning VLANs? I would like to come up with a scheme where the subnetting could identify the physical floor or link or switch.

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New Member

Re: Subnetting scheme for 3550 L3 in the wiring closet

The first thing that you need to do is to determine how many VLANs you need. You do this by looking at logical separations such as by department, building, floor, etc. The number of VLANs will tell you how many subnets you need (one per VLAN). You then have to look at each VLAN to see how many users will be connected to them. Having done this you will know how many subnets you need and how many host per subnet. For example: Lets assume that your 16 switches are spread over 8 floors, two per floor, and you have decided that separation of VLANs by floor (one VLAN per floor) is the best method. Lets ferther assume that no floor will have more than 200 hosts (servers, workstations, printers, etc.). You now know that you need 8 VLANs with 200 hosts per VLAN. The next step is to develop an addressing scheme. A simple method would be to use 192.168.X.X/24. This would give you 254 subnets with 254 hosts per subnet. If you feel that you would like to have more spare host addresses for growth, you might try 172.16.X.X/23. This would give 126 subnets, each with 510 hosts. As you can see, there are many ways to achomplish the required result. Your preference will dictate the exact scheme that you use. I hope that this helps.

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