Case Study (Corporate Headquarters)

IP Addressing Plan for IP Telephony

The objective of the IP addressing plan for IP telephony is to use a network range which is scalable, and also not currently being used in XYZ network. There is an assumption that there is no need for this address range to be advertised to the outside world. As a result, RFC 1918 private addresses can be utilized. The 10.x.x.x/8, Class A address range meets these requirements.

Subnets will be created in this address range based on the following:

       Number of subnets per hub site

       Number of IP phones per subnet

       Number of core routes

       IP route summary plan

Based upon the above requirements, the following IP addressing plan is proposed:

Subnet the 10.x.x.x/8 range to Class B addresses and assign a Class B address to each hub site.

For example:

New Jersey        

New York          

Washington D.C.



Los Angeles       



This allows 256 subnets (Class C), each with 254 hosts, per hub site. Several Class C subnets can also be combined to get larger number of hosts. For example, consider the New York block: will provide a subnet with 8,000 hosts and also in addition will have 224 Class C subnets left.

In the extreme case, when all the subnets in the Class B address range for the hub site are used, additional Class B address can be used for that particular hub site. 

This plan also will lead to good route summarization, since each hub site will only have one Class B route associated with it.

IP Addressing Plan

The Class B address has been reserved for IP Telephony in New York. The first 100 ( to will be reserved for the main 5x2 office. The XYZ offices off of HQ will be assigned IP addresses beginning from, and so on

Each floor in the building will have 2 IDF closets, with one or two Catalyst 4000 per closet. The IP Phones will be distributed to one of the closets, depending upon their geographical location.  Each Catalyst switch will have an exclusive aux Vlan for IP Phones. This Vlan will have a 25 bit 10.2.x.x address associated with it. This allows for 126 devices per Vlan. So, this allows for approximately 250 voice devices to be operational per floor. The Class B address has been reserved for IP Telephony in New York.  


Floor Number

IDF Closet 1

IDF Closet 2

Floor 37 *R

Floor 36

Floor 35

Floor 34

Floor 33

Floor 32

Floor 31

Floor 30

Floor 29

Floor 28

Floor 27

Floor 26

Floor 25

Floor 24

Floor 23 *R

Floor 22

Floor 21

Floor 20

Floor 19


Floor 17

Floor 16 *R

Floor 15

Floor 14

Floor 13

Floor 12

Floor 11

Floor 8

Floor 7

Floor 6

Floor 5

Floor 4

Floor 3

Level C-1

Level C-2


IP Addressing Plan for Medium Branch Office will be assigned to the medium branch office.


IP Addressing Plan for Small Branch Office

5 class C blocks will be reserved for small branch -