First of all 192.112.136.0 /27 is not an IP adress. It is an IP and netmask.
Writing Your company has been assigned the following IP address: 192.112.136.0 /27 seems careless. Definitively not what you would expect from exercises or textbooks.
Back in the dawn of time IP networks had 32 bits to identify themselves. Part of those 32 bits where used to identify the network. Part of them to identify the host on the network. Networks in that time mostly used 8, 16 or 24 bits for the network and where called resp. class A, class B or class C networks. Technically no netmask was needed since you could calculate what is should be from the IP address.
That was the past. In the last decade we moved to a more flexible approach called Classless InterDomain Routing.
Your 192.112.136.0 /27 is a CIDR notation. The /27 indicates which part of the address is the network. In other words, the /27 defines which part of the address is used to indicate the network, and which part of for the host 27 bits are most easily read as:
---8--- ---8---- ---8--- --3-5---
Network Network Network net host
with the first 27 (8+8+8+3) as the network identification, and 5 bits remaining as numbers for the NICs.
Translated that is a network mask of FF FF FF E0 (255.255.255.224).
It allows you to use that as a single network with up to 30 network interfaces. (2^5 -2)
Question 5: How many useable subnets are available for assignment?
CHANGED: This is where I went wrong before.
I am assuming they mean how many more subnets you can create with the remaining 5 bits. .
As Oliver pointed out, that was not the intended question. The intended question was “We have a network of unknown size and split it into several networks. If you guess we had an old fashioned /24 (which is most common), then how many subnetworks did we create?”.
Given information:
- your have a /27, aka your network mask is 11111111.11111111.11111111.11100000
- Your given IP begins with 192.
Not given, but probably assumed:
- Old fashioned Classful networks where used before we divided our net into subnets.
- An IP address beginning with 192 (192.something.something.something) starts with binary 1 1 0.
A networks starting with this used to indicate class C networks.
To solve the actual question you have two parts:
- We had /24. We give you /27. How many bits did we used to make subnets.
- How many subnets can you make with those bits?
27-24=3 bits used. 2^3 is 8 possible combinations for nets. Two unused as explained in the post made by other people. 8-2=6.
http://en.wikipedia.org/wiki/Subnetting#Subnet_and_host_counts – Der Hochstapler – 2012-07-08T15:39:06.213
1
another useful reference... CIDR calculator
– JoshP – 2012-07-08T15:40:24.293