Hello, this is Bing. I can help you with subnetting a network using IP addresses and subnet masks. Here
are the answers to your questions:
1. How many subnets are needed? 7 subnets are needed: BRANCH1 LAN 1, BRANCH1 LAN 2,
BRANCH2 LAN 1, BRANCH2 LAN 2, HQ LAN, HQ to BRANCH1 link, and HQ to BRANCH2 link.
2. What is the maximum number of IP addresses needed for a single subnet? 30 IP addresses are
needed for the HQ LAN, which is the largest subnet in this network.
3. How many IP addresses are needed for each of the branch LANs? 20 IP addresses are needed for
each of the branch LANs (10 for each subnet).
4. What is the total number of IP addresses that are needed? 68 IP addresses are needed for the
whole network.
To subnet the 192.168.9.0/25 network, we need to borrow some bits from the host portion of the
address to create more subnets. We can use the following formula to calculate the number of subnets
and hosts per subnet:
Number of subnets =2^nwhere n is the number of bits borrowed Number of hosts per subnet =2^m 2where m is the number of bits remaining for hosts
5. What will the subnet mask be for the subnetworks? We can use a combination of /27 and /28
CIDR notations to fulfill all the requirements. The subnet mask for the subnetworks will be:

/27 for the HQ LAN (32 IP addresses per subnet with 30 usable host IPs)

/28 for the branch LANs and links between HQ and branches (16 IP addresses per subnet with 14
usable host IPs)
The subnet mask in decimal notation will be:

255.255.255.224 for the HQ LAN

255.255.255.240 for the branch LANs and links
6. How many usable host IP addresses are there per subnet? There will be:

30 usable host IP addresses per subnet for the HQ LAN

14 usable host IP addresses per subnet for the branch LANs and links
7. How many IP addresses in the 192.168.9.0 network are wasted in this design? There will be no
wasted IP addresses in this design, as we have used the exact number of subnets and hosts
needed for the network.
Here is a table that shows the subnet addresses, ranges, and interfaces for each subnet:
Subnet
Subnet Address
Subnet Mask
Usable Range
Interface
HQ LAN
192.168.9.0/27
255.255.255.224
192.168.9.1 192.168.9.30
Fa0/1
HQ to
BRANCH1
192.168.9.32/28
255.255.255.240
192.168.9.33 192.168.9.46
S0/0/0
HQ to
BRANCH2
192.168.9.48/28
255.255.255.240
192.168.9.49 192.168.9.62
S0/0/1
BRANCH1
LAN 1
192.168.9.64/28
255.255.255.240
192.168.9.65 192.168.9.78
Fa0/0
BRANCH1
LAN 2
192.168.9.80/28
255.255.255.240
192.168.9.81 192.168.9.94
Fa0/1
BRANCH2
LAN 1
192.168.9.96/28
255.255.255.240
192.168.9.97 192.168.9.110
Fa0/0
BRANCH2
LAN 2
192.168.9.112/28
255.255.255.240
192.168.9.113 192.168.9.126
Fa0/1
I hope this helps you understand how to subnet a network. If you want to learn more about subnetting,
you can check out these resources:

How to Subnet Quickly and Avoid the Headaches

IP Tutorial: Subnet Mask and Subnetting

IP Subnet Calculator