SubNet_Chat - The Cisco Learning Network

navybeansvietnameseNetworking and Communications

Oct 24, 2013 (3 years and 8 months ago)

91 views


1

Ths is an Internet Protocol (IPv4) Subnet Chart. You can use this to quickly look up how your
might need to subnet your network. At the bottom there is a quick how
-
to on calculating
subnets.

For more information on subnetting, see
RFC 1817

and
RFC 1812
.

Class address ranges:



Class A = 1.0.0.0 to 126.0.0.0



Class B = 128.0.0.0 to 191.255.0.0



Class C = 192.0
.1.0 to 223.255.255.0

Reserved address ranges for private (non
-
routed) use (see
RFC 1918
):



10.0.0.0
-
> 10.255.255.255



172.16.0.0
-
> 172.31.255.255



192.168.0.0
-
> 192.168.255.25
5

Other reserved addresses:



127.0.0.0 is reserved for loopback and IPC on the local host



224.0.0.0
-
> 239.255.255.255 is reserved for multicast addresses

Chart notes:



Number of Subnets
-

"( )" Refers to the number of effective subnets, since the use o
f
subnet numbers of all 0s or all 1s is highly frowned upon and RFC non
-
compliant.



Number of Hosts
-

Refers to the number of effective hosts, excluding the network and
broadcast address.


Class A

Network Bits

Subnet Mask

Number of Subnets

Number of Hosts

/8

255.0.0.0

0

16777214

/9

255.128.0.0

2 (0)

8388606

/10

255.192.0.0

4 (2)

4194302

/11

255.224.0.0

8 (6)

2097150

/12

255.240.0.0

16 (14)

1048574

/13

255.248.0.0

32 (30)

524286

/14

255.252.0.0

64 (62)

262142

/15

255.254
.0.0

128 (126)

131070

/16

255.255.0.0

256 (254)

65534


2

/17

255.255.128.0

512 (510)

32766

/18

255.255.192.0

1024 (1022)

16382

/19

255.255.224.0

2048 (2046)

8190

/20

255.255.240.0

4096 (4094)

4094

/21

255.255.248.0

8192 (8190)

2046

/22

255.255.252.0

16384 (16382)

1022

/23

255.255.254.0

32768 (32766)

510

/24

255.255.255.0

65536 (65534)

254

/25

255.255.255.128

131072 (131070)

126

/26

255.255.255.192

262144 (262142)

62

/27

255.255.255.224

524288 (524286
)

30

/28

255.255.255.240

1048576 (1048574)

14

/29

255.255.255.248

2097152 (2097150)

6

/30

255.255.255.252

4194304 (4194302)

2

Class B

Network Bits

Subnet Mask

Number of Subnets

Number of Hosts

/16

255.255.0.0

0

65534

/17

255.255.12
8.0

2 (0)

32766

/18

255.255.192.0

4 (2)

16382

/19

255.255.224.0

8 (6)

8190

/20

255.255.240.0

16 (14)

4094

/21

255.255.248.0

32 (30)

2046

/22

255.255.252.0

64 (62)

1022

/23

255.255.254.0

128 (126)

510

/24

255.255.255.0

25
6 (254)

254

/25

255.255.255.128

512 (510)

126

/26

255.255.255.192

1024 (1022)

62

/27

255.255.255.224

2048 (2046)

30

/28

255.255.255.240

4096 (4094)

14


3

/29

255.255.255.248

8192 (8190)

6

/30

255.255.255.252

16384 (16382)

2

Cl
ass C

Network Bits

Subnet Mask

Number of Subnets

Number of Hosts

/24

255.255.255.0

0

254

/25

255.255.255.128

2 (0)

126

/26

255.255.255.192

4 (2)

62

/27

255.255.255.224

8 (6)

30

/28

255.255.255.240

16 (14)

14

/29

255.255.255.248

32 (30)

6

/30

255.255.255.252

64 (62)

2



Supernetting (CIDR) Chart




CIDR
-

Classless Inter
-
Domain Routing.



Note: The Number of Class C networks must be contiguous.

For example, 192.169.1.0/22 represents the following block of addresses:

192.169.
1.0, 192.169.2.0, 192.169.3.0 and 192.169.4.0.

Class C

CIDR Block

Supernet Mask

Number of Class C Addresses

Number of Hosts

/14

255.252.0.0

1024

262144

/15

255.254.0.0

512

131072

/16

255.255.0.0

256

65536

/17

255.255.128.0

128

32768

/
18

255.255.192.0

64

16384

/19

255.255.224.0

32

8192

/20

255.255.240.0

16

4096

/21

255.255.248.0

8

2048

/22

255.255.252.0

4

1024

/23

255.255.254.0

2

512


4




Quick Subnetting How
-
To (Thanks to
Jason
@

GeekVenue.)



[Understanding decimal
-

Base 10]


The first thing you must know is that the common number system used world wide is the
decimal system

(otherwise known a
s
base 10
). What makes the decimal system a base 10
system is that it is
based on grouping numbers by 10's
. It is believed that the system
evolved because we have ten fingers and ten toes which over the years we have used for
counting. I use mine all the t
ime (grin). We name the ten digits: zero, one, two, three, four,
five, six, seven, eight and nine.


The decimal system has a
1
's place, a
10
's place, a
100
's place, a
1000
's place and so on.
We say the number places are grouped by 10's because
multiplying
each number place by
10 gives you the next number place
. So: 1x10=10 (the 10's place), 10x10=100 (the 100's
place), 100x10=1000 (the 1000's place) etc.


Let's look at the decimal number
103

by place.


103

<
-

read from right to left


We have a
3

in the
1's
place

We have a
0
in the
10's place

We have a
1

in the
100's place


Thus:
100+0+3=103


By now you probably feel like you have attended Kindergarten for the second time in your life?
Sorry about that but it is very important that you understand the concept o
f what a number
system is, and what it is based on before we look at binary.



[Understanding binary
-

base 2]



Binary is a
base 2

system, and thus groups numbers by 2's and not by 10's like the decimal
system. We name the two digits: zero and one. The b
inary system has a
1
's place, a
2
's place,
a
4
's place, an
8
's place, a
16
's place and so on. We say the number places are grouped by
2's because
multiplying each number place by 2 gives you the next number place
. So:
1x2=2 (the 2's place), 2x2=4 (the 4's
place), 4x2=8 (the 8's place), 8x2=16 (the 16's place)
etc.


Let's look at the decimal number Let's look at the decimal number
103

in
binary format
:


01100111

<
-

read from right to left


We have a
1

in the
1's place

We have a
1

in the
2's place

We have a
1

in the
4's place

We have a
0

in the
8's place

We have a
0

in the
16's place

We have a
1

in the
32's place

We have a
1

in the
64's place


5

We have a
0

in the
128's place


Thus:
0+64+32+0+0+4+2+1=103


Okay, Let's test your skills. Here is a list of binary nu
mbers, try converting them to decimal
and check your answers at the end of this post.


10000000

11000000

11100000

01000000

10000011

10010001

11111111


If you were able to convert these numbers to decimal then congratulations! You're ready to
move on

to the next section.



[Understanding a subnet mask]


Now that you understand what binary is, let's have a look at our two subnet masks from the
beginning of my post:


192.168.1.0 / 255.255.255.0

192.168.1.0/24


The concept of a subnet mask is simple. Yo
u have a network and you have hosts on the
network (anything with an IP address is a host).
The subnet mask determines what
portion of the TCP/IP address represents your network and what portion can be
used for your hosts
. Because I am a simple person, I t
hink of it like this; The network
number represents the street I live on, and the host portion is used for the numbers on all the
houses on my street.


A subnet mask of
255.255.255.0

means that the first
three

octets of the address will be used
for the ne
twork, and thus our network number is
192.168.1
. This means we can have
254

computers on this network, because the fourth octet is not being used by the network portion
of the address. We know this because of the
0
in the subnet mask (255.255.255.
0
).


We
call each of the number sections an
octet

because we think of them in binary, and there
are eight possible bits in each section. Eight bits is an octet.
11111111

in binary is
255

in
decimal (did you do the conversions?). So our decimal subnet mask 255.255.
255.0 displayed
in binary is going to be:


11111111.11111111.11111111.00000000


If you count all the ones, you will find that there are
24

of them. Now look at the subnet mask
examples again.


192.168.1.0/255.255.255.0

192.168.1.0/24


Do you see why
both
subnet masks are the same
? The number
24

is the number of
bits

used
in the network portion of the address, and is short
-
hand for writing the address/subnet mask
combination. It becomes important to understand this when you start dividing your network
into
multiple sub networks.




6

[Understanding Subnetting]


Before reading this section, you should have a
good understanding

of what a subnet mask is
and how binary bits represent the subnet mask.


Simply put, subnetting is
dividing your network into
multiple s
ub networks
. To go back to
my silly example about houses and streets, subnetting gives you multiple streets in your
neighborhood.


There are
two methods

for dividing your network into multiple sub networks; One is to simply
change your network numbers keep
ing the same subnet mask. The other is to subnet your
network into smaller sub networks.


Keeping the same mask:

Your network could be divided into two or more networks by changing the network portion of
the address such as
192.168.1

and
192.168.2

and keep
ing the same subnet mask.


Example:

192.168.1.0/255.255.255.0

192.168.2.0/255.255.255.0


Doing this would give you
two separate networks

with
254 hosts per network
. This is a
very common method of dealing with multiple networks. However, back in the good o
ld days
you had to pay for every IP address you used, and if you had 25 computers on your network
you probably would not want to pay for 254 addresses! The answer to the problem
is...subnetting.


Subnetting a network:

Subnetting is when you use bits from t
he host portion of your address as part of
your network number
. This let's you subdivide your network at the cost of host addresses,
which is great if you're paying for every host IP address. It will save you money because you
pay for fewer TCP/IP addresse
s. Confused? Here is where understanding binary is important.


Lets look at a new subnet mask:

255.255.255.224


As you can see in the fourth octet, some of the host portion of this subnet mask is now being
used for part of the network address. Which means
we are
now using some of the binary
bits in the fourth octet for our network numbers
, and that gives us fewer hosts than our
old mask (which gave us 254), but gives us more networks (which is why we call it
subnetting).


How can we tell how many networks
and hosts per network this new subnet mask will give us?
Well... we shall have to use some of our newly acquired binary skills.


The
first task

is to find out
how many bits in the fourth octet are being used
? The
decimal number is 224, what is the decimal
number 224 as represented in binary?


The decimal number
224

in binary is:

11100000


We have a
0

in the
1's place

We have a
0

in the
2's place

We have a
0

in the
4's place

We have a
0

in the
8's place

We have a
0

in the
16's place

We have a
1

in the
32's
place

We have a
1

in the
64's place


7

We have a
1

in the
128's place


Thus: 128+64+32+0+0+0+0+0=
224



So our complete subnet mask in binary is:

1111111.11111111.11111111.
11100000


We now know that three bits from the fourth octet are used. How can we tell ho
w many sub
networks we're going to have? This requires some math
-

sorry. The formula is:
2
n
-
2
, where
n

is the
number of bits being used from the host portion

of our subnet mask.


Note:

We
subtract 2 from the total

because you do not count all 0's or all 1
's.


The formula for
three bits

is:

2
3
-
2
=6


In simpler terms:

(2x2x2)
-
2
=6


So our network is
sub divided into 6 networks
. Next, we want to know what the network
numbers are, and how many hosts we can have on each of the 6 networks?


What is the first subne
t? Let's have a look at the bits in our
fourth octet

again. The bit that
gives us the answer is the
(1) closest to the first zero
, and in this case it is the 3rd bit from
the left.


11
1
00000


The 3rd bit will
start our first network
, and the 3rd bit is in
the
32
's place (remember binary).
Start adding the value 32 to itself six times to get the six network numbers.


Note:

A quicker way to find our starting network number is to
subtract our mask from 256
.

256
-
224
=32


Here are our network numbers:


32

64

96

1
28

160

192


A better way to display this is:


192.168.1.
32

192.168.1.
64

192.168.1.
96

192.168.1.
128

192.168.1.
160

192.168.1.
192


The host addresses will
fall between the network numbers
, so we will have
30

hosts per
network. You're probably wondering why i
t's
not

31? The answer is that the last address of
each subnet is used as the
broadcast address

for that subnet.


Example:

Subnet:
192.168.1.32 / 255.255.255.224


8

Address Range:

192.168.1.33 through 192.168.1.62 (30 hosts)

Subnet Broadcast Address:
192.168.1
.63


Quiz:

Let's test your skills
-

write the address range and broadcast address for the following subnet.
You will find the answer at the end of this post.


Subnet:

192.168.1.128 / 255.255.255.224

Address Range
?

Subnet Broadcast Address
?


If we we're pa
ying for our TCP/IP addresses, we would only pay for one network and host
combination, thus paying for 30 hosts and
not

254. It could mean some real savings, it also
frees up the remaining addresses for other organizations to use.


Let's look at another su
bnet mask:

255.255.255.240


How many bits are used from the host portion? To find this out, we need to know how the
decimal number 240 is represented in binary.


The answer is:

11110000


So four bits are taken from the host portion of our mask. We do the
same math as before:


2
4
-
2
=14


In simpler terms:

(2x2x2x2)
-
2
=14


We will have
14 sub networks
, and what will the network numbers be? Look at the
fourth
bit
, it's in the 16's place:

111
1
0000


Note:

A quicker way to find our starting network number is to
su
btract the value of our mask
from 256
. So:
256
-
240
=16


Start adding 16 to itself
-

fourteen times to get all 14 network numbers:


16

32

48

64

80

96

112

128

144

160

176

192

208

224


A better way to display our subnets is:


192.168.1.16


9

192.168.1.32

192.168.1
.48

192.168.1.64

192.168.1.80

192.168.1.96

192.168.1.112

192.168.1.128

192.168.1.144

192.168.1.160

192.168.1.176

192.168.1.192

192.168.1.208

192.168.1.224


The host addresses fall between the network numbers. So we will have 14 host addresses on
each of ou
r 14 sub networks (
remember
: the last or 15th address is the broadcast address for
that subnet).


If you had a small company with 10 hosts and needed to have a static IP address for all of
your hosts, you would be assigned a network/subnet mask and a valid

IP address range.


Here is an example of what that might look like:


Network
: 205.112.10.16/.255.255.255.240

Address Range
: 205.112.10.17 through 205.112.10.30

Subnet Broadcast Address
: 205.112.10.31



[Answers to Binary Conversions]


10000000 = 128

1100
0000 = 192

11100000 = 224

01000000 = 64

10000011 = 131

10010001 = 145

11111111 = 255



[Answer to Subnet Question]


Subnet:
192.168.1.128 / 255.255.255.224

Address Range:

192.168.1.129 through 192.168.1.158

Subnet Broadcast Address:

192.168.1.159