DCN286 INTRODUCTION TO DATA COMMUNICATION TECHNOLOGY

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DCN286
INTRODUCTION TO DATA
COMMUNICATION TECHNOLOGY


IP Routing and subnet


TCP/IP model

Application

Transport

Internet

Network

Interface

Application

Presentation

Session

Transport

Network

Data Link

Physical

TCP/IP protocol suite

TCP/IP Internet Layer


Defines how to deliver data from one host to
another on various physical networks:

1.
Logical addressing

2.
Routing and routing protocol

3.
Main protocols: IP, ARP, RARP (Reverse Address
Resolution Protocol), ICMP (Internet Control
Message Protocol) and router protocols such as
RIP (Routing Information Protocol) and OSPF
(Open Shortest Path First).

4.
PDU (Protocol Data Unit) is packet in layer 3

Switching

1.
Switching is redirecting according to MAC
address.

2.
Switching is functioning only in Ethernet.
(Please recall that Data Link header is also
called as Ethernet header.)

3.
Switching is in layer 2 Data Link layer

4.
Switching is faster than routing

5.
Switch can separate collision domain.


Routing


If all traffics are in the same LAN (subnet), no
routing is required. The computers talk to
each other over network cable directly.


Only internetwork (between different
networks), the routing is required.


Router can divide broadcast domain.


Router can offer stronger security protection.


Routing table could be updated by i) network
engineer manually, or ii) routing protocols
dynamically.

Routable and routing procotol


Routable protocol: To redirect (forward)
traffic to other networks according to the
routing path defined by routing protocol.
Example: TCP/IP, IPX/SPX.


Routing protocol: To dynamically define,
update and distribute the best (lowest cost)
routing path between networks. Example:
RIP, IGRP, EIGRP, OSPF and BGP, etc, etc.


Routing table is to contain the final
information. It is possible to have multiple
entries with same routing costs.

Routing table


is a small in
-
memory database
managed by the
router's built
-
in
hardware and
software


Contains
destination
network
information

Example of routing table

Router


Router (pronounced
/'rautər/

in the USA
and Canada, pronounced
/'ru:tə/

in the UK
and
Ireland
, or either pronunciation in
Australia): a
networking

device whose
software and hardware are usually tailored
to the tasks of
routing

and
forwarding

information.


To be able to route packets, a router must
know, at a minimum, the following:



Destination address


Neighbor routers from which it can learn
about remote networks


Possible routes to all remote networks


The best route to each remote network


How to maintain and verify routing
information

Routing process (1)

2. Router de
-
encapsulate packet (TTL
-
1)

Ethernet Header

IP Packet

Trailer

Preamble

7 bits

SFC

1 bit

Destination

6

Source

6

Length

2

Data and
Pad

46
-
1500

FCS

4

1. Router receive frame

Routing process (2)

4. Find out MAC address of destination interface by ARP

3. Router review routing table and find the right path
including the next interface to which the packet
needs to be sent to

5. Re
-
encapsulate the IP packet in a new frame with the
new source and destination MAC address. In the new
frame, IP address information does not have change.

6. Send out the frame from the destination interface

Static routing


Routing table could be updated by i) network engineer
manually, or ii) routing protocols dynamically.


Static route is to use command manually create or update
routing entries in routing table.


Pros:

1.
Securer (Only network engineer can modify)

2.
Faster (No need for any further processing or calculation)

Cons


Hard to expand


Wrongly configure is hard to troubleshooting


Routing table fields

1.
Source

2.
Subnet

3.
Mask

4.
Out Int (Output Interface)

5.
Next
-
Hop (forward destination)

IP Route command (1)
-

Optional

To specify routes by output interfaces:


router>en

Router#conf t

Router(config)#ip route 10.1.10.0
255.255.255.0 s0/0



IP Route command (2)
-

Optional

Determine next hope


router>en

Router#conf t

Router(config)#ip route 10.1.10.0
255.255.255.0 10.1.11.1

IGP
(Interior Gateway Protocols)
/
EGP
(Exterior Gateway Protocols)



Routing protocols could be divided in Interior
or Exterior routing protocols.

1.
IGP (Interior Gateway Protocols) works in a
single Autonomous System (AS). Examples
are RIP, OSPF, IGRP, EIGRP, etc, etc.

2.
EGP (Exterior Gateway Protocols) works
between Autonomous Systems. The only
viable example is BGP (Border Gateway
Protocol)

Route table calculation (optional)


Each

router


contains


two


lists:


Tentative



and


Confirmed


Each


list


contains


a


set


of


triples
-

(Destination,


Cost,


NextHop)


Note


that


"NextHop"


is


the


first


router


on


the


path


from


the


source


S


to


Destination


After calculation, each router would build up
its own list.



Routing updates


Periodically update



Declare route unusable without updates



Remove route entry after it was not usable
for sometimes.


VLSM (Variable Length Subnet
Mask)


Different to traditional classful subnet mask
(class A


255.0.0.0; class B


255.255.0.0;
class C


255.255.255.0), VLSM is to support
subnet and it is classless as its network mask
could be 255.255.224.0.


Old routers only support classful routing. The
network mask is not included in routing update
information. New router supports VLSM and
mask is a part of update information.

Valid network mask



Binary value

Decimal value

00000000

0

10000000

128

11000000

192

11100000

224

11110000

240

11111000

248

11111100

252

11111110

254

11111111

255

IP address class

Traditionally, the IP address was classified in classes:

Class A: network 1


126 with subnet mask 255.0.0.0
(Initial bit starts as 0)

Class B: network 128


191 with subnet mask
255.255.0.0 (Initial bit starts as 10)

Class C: network 192


223 with subnet mask
255.255.255.0 (Initial bit starts as 110)

Class D: network 224


239 (Initial bit starts as 1110)
for multicast IP address

Class D: network 240


255 (Initial bit starts as 1111)
experimental use

The
special
network 0 and127 are not in
cluded in

those official classical IP address
. 127.0.0.1 is the
loopback address which is used to test TCP/IP
stacks.

Subnet


Subnet is to logically divide your network into many
sub networks.


In the same subnet, traffic is “local” and not gateway
(router) is required. Network hosts would use ARP
table for the MAC

address of the destination machine
and send the packet to it accordingly. If it is not local,
packets would be forwarded to default gateway for
future routing (redirecting).


In addition, the broadcast would be limited to the small
subnets leading to less “noise” in the network traffic.


You can also use subnet to logically specify hosts for
different departments. (for security control, connection,
asset management, etc, etc)

Power calculation of 2

The powers of 2

Decimal value

Binary Value

2^0

1

00000001

2^1

2

00000010

2^2

4

00000100

2^3

8

00001000

2^4

16

00010000

2^5

32

00100000

2^6

64

01000000

2^7

128

10000000

2^8

256

100000000

2^9

512

1000000000

2^10

1024

10000000000

2^11

2048

100000000000

2^12

4096

1000000000000

2^13

8192

10000000000000

Subnet calculation


Network address design would decide how
many subnets would be yield for the
additional subnet mask.


Or, network design needs to make sure how
many hosts could be placed in each subnet.


Based on subnet calculation, find out
network address and broadcast in each
subnet. (Those two IP address cannot be
used by any host.)

Several terms


Subnet number: The numerically lowest number in a
subnet to present the IP Subnet.


Subnet broadcast address: The numerically highest
number in a subnet. If a packet is sent to this address, it
would be forwarded to all hosts in the IP Subnet.


Subnet zero (zero subnet): The numerically smallest
subnet number in any subnet scheme. It has all “0” in
subnet portion. With classful IP addressing, it is one of the
two reserved subnets and should not be used.


Broadcast subnet: The numerically largest subnet number
in any subnet scheme. It has all “1” in subnet portion. With
classful IP addressing, it is one of the two reserved
subnets and should not be used.


Define subnet number


Subnet bits (“1”) can tell how many subnet could be produced by the
mask. The formula is 2^(number of subnet “1” bits)
-

2

Original classfull network mask:


Class A network has the form N.H.H.H, the default subnet mask is 8 bits
long.


Class B network has the form N.N.H.H, the default subnet mask is 16
bits long.


Class C network has the form N.N.N.H, the default subnet mask is 24
bits long.


The additional subnet bits can generate subnet. For instance, You have an
IP of 156.233.0.0 with a subnet mask of 7 bits. How many hosts and
subnets are possible?


There is additional 7 bits to the default subnet mask.
The total number of
bits in subnet are 16+7 = 23.

This leaves us with 32
-
23 =9 bits for
assigning to hosts.
7 bits of subnet mask corresponds to (2^7
-
2)=128
-
2
= 126 subnets.

9 bits belonging to host addresses correspond to (2^9
-
2)=512
-
2 = 510 hosts.

Define host number in each subnet


Subnet bits (“0”) can tell how many host could be contained in each
subnet. The formula is 2^(number of host “0” bits)
-

2

Original classfull network mask:


Class A network has the form N.H.H.H, the default host mask is 24 bits
long.


Class B network has the form N.N.H.H, the default host mask is 16 bits
long.


Class C network has the form N.N.N.H, the default host mask is 8 bits
long.


The additional subnet bits can generate subnet. For instance, You have an
IP of 156.233.0.0 with a subnet mask of 7 bits. How many hosts and
subnets are possible?


There is additional 7 bits to the default subnet mask. The total number of
bits in subnet are 16+7 = 23.
This leaves us with 32
-
23 =9 bits for
assigning to hosts.

7 bits of subnet mask corresponds to (2^7
-
2)=128
-
2
= 126 subnets.
9 bits belonging to host addresses correspond to (2^9
-
2)=512
-
2 = 510 hosts.

Increment Number in Class C


Increment number (magic #) is 2^(8
-
number_of_subnet_bits). Or, 256


subnet
mask.

For instance, You have an IP of 192.168.42.0 with
a subnet mask of 3 bits. What is the increment
number?


Beside the traditional class C network mask
255.255.255.0. The 3 bits means that the mask
is 255.255.255.224. Increment number is 256


224 = 32.

Or, 2^(8
-
3) = 32


Increment Number in Class B (1) optional

Class B


borrowing in the 3rd octet




156.233.0.0 Borrow 3 bits Subnet Mask = 255.255.224.0



Number of networks created 2^3
-
2 = 6 (Microsoft way is 2^3=8)


Number of useable networks created 2^3 = 8


2 = 6



Number of host per network 2^5 X 256 = 8192



The increment for each network is 32 in the 3rd octet (the number of unmasked bits
in the 3rd octet is 5, this is the octet we borrowed from)



If you need to determine the network number of subnet 6, multiply 6 X 32 = 192.
The subnet 6 network address would be 156.233.192.0




If you are borrowing in the 3rd octet, just ignore the 4
th

octet to determine your
network numbers.

Increment Number in Class B (2) optional


Class B


borrowing all the 3rd octet



156.233.0.0 Borrow 8 bits Subnet Mask = 255.255.255.0



Number of networks created 2^8 = 256


Number of useable networks created 2^8
-

2 = 256


2 = 254



Number of host per network 2^0 X 256 = 256



The increment for each network is 256 in the 3rd octet. (The number of unmasked
bits in the 3rd octet is 0, this is the octet we borrowed from. This means that the
value of the 3rd octet increases by one each time.)



If you need to determine the network number of subnet 26, simply insert that
number into the 3rd octet slot. The subnet 26 network address would be
156.233.26.0



If you need to determine the network number of subnet 100, simply insert that
number into the 3rd octet slot. The subnet 100 network address would be
156.233.100.0

Increment Number in Class B (3) optional


Class B


borrowing in the 4th octet






156.233.0.0 Borrow 11 bits Subnet Mask = 255.255.255.224



Number of networks created 2^11
-
2 = 2046 (or 2^3 X 256
-
2 = 2048
-
2 = 2046)


Number of useable networks created 2^11
-
2 = 2048


2 = 2046


Number of host per network 2^5 = 32


The increment for each network is 32 in the 4th octet. (The number of masked bits in the 4th octet is 3, the
number of unmasked bits in the 4th octet is 5, this is the last octet we borrowed from. This means that the
value of the 4th octet increases by the increment value.)

1.

If you need to determine the network number of subnet 325, do the following:


Divide the desired subnet by 2 raised to the masked bits in the 4th octet


325 / 2^3 or 325 / 8 = 40 remainder 5


The 40 is the value of the 3rd octet
--

156.233.40.?


To find the value of the 4th octet multiply the remainder (5) times the increment (32)


32 X 5 = 160 This is the value of the 4th octet


The subnet 325 network address would be 156.233.40.160


--------------------------------------------------------------------------------

2.

If you need to determine the network number of subnet 40, do the following:


Divide the desired subnet by 2 raised to the masked bits in the 4th octet


40 / 2^3 or 40 / 8 = 5 remainder 0


The 5 is the value of the 3rd octet
--

156.233.5.?


To find the value of the 4th octet multiply the remainder (0) times the increment (32)


32 X 0 = 0 This is the value of the 4th octet


The subnet 40 network address would be 156.233.5.0

Find the subnet address info


Increment number (magic #) is 2^(8
-
number_of_subnet_bits). Or, 256


subnet mask.


The zero subnet is as same as the original
classful network address


Add increment number to the zero subnet will get
1
st

subnet number, adding increment number to
1
st

subnet will get 2nd subnet number, etc, etc,.


Broadcast address of each subnet is the address
before next subnet number.


After define the subnet number and broadcast
address in the subnet, the address range for the
host will be defined in the subnet.


Subnet calculation example

192.168.10.0/27 (255.255.255.224)

2^3


2 = 6 subnets

Increment number is 256
-
224=32



# of subnet

Subnet

Lowest HOST IP
address

Highest HOST IP
address

Broadcast
address

0

192.168.10.0

192.168.10.1

192.168.10.30

192.168.10.31

1

192.168.10.32

192.168.10.33

192.168.10.62

192.168.10.63

2

192.168.10.64

192.168.10.65

192.168.10.94

192.168.10.95

3

192.168.10.96

192.168.10.97

192.168.10.126

192.168.10.127

4

192.168.10.128

192.168.10.129

192.168.10.158

192.168.10.159

5

192.168.10.160

192.168.10.161

192.168.10.190

192.168.10.191

6

192.168.10.192

192.168.10.193

192.168.10.222

192.168.10.223

Broadcast
subnet

192.168.10.224

192.168.10.225

192.168.10.254

192.168.10.255

Boolean AND

When two bits (binary numbers) are in such
logical calculation:

If both bits are 1, final result is 1. Otherwise,
final result is 0.


For example, 1 + 1 = 1; 1 + 0 = 0; 0 + 1=0


0 + 0 =0


Find resident subnet


Convert the questioned host IP address and subnet mask
into binary. Add them together by using Boolean AND
calculation. Convert binary result to decimal value and it
presents the resident subnet of the host.

Which subnet is 192.168.10.100 in when subnet mask is
255.255.255.224?


1
st

Octet

2
nd

Octet

3
rd

Octet

4
th

Octet

IP address
192.168.10.100

11000000

10101000

00001010

01100100

Mark
255.255.255.224

11111111

11111111

11111111

11100000

Calculation Result

11000000

10101000

00001010

01100000

Decimal of the
subnet number

192

168

10

96

Subnet calculation clarification

In real world, you may hear the argument of
subnet calculation:


Microsoft: Number of subnets: 2^(number
-
of
-
subnet
-
bits) This is the number of
subnets that are created.



Cisco: Number of subnets: 2^(number
-
of
-
subnet
-
bits


2) This is the number of
subnets you can use to connect devices.

Network address questions

W
rite the subnet, broadcast address, and valid
host range for each of the following:


1.
172.16.10.5 255.255.255.128


2.
172.16.10.33 255.255.255.224


3.
172.16.10.65 255.255.255.192


4.
172.16.10.17 255.255.255.252


5.
172.16.10.33 255.255.255.240


6.
192.168.100.25 255.255.255.252


7.
192.168.100.17, with 4 bits of subnetting


8.
192.168.100.66, with 3 bits of subnetting


9.
192.168.100.17 255.255.255.248


10.
10.10.10.5 255.255.255.252

Answer of q1

1.
172.16.10.5 255.255.255.128: Subnet is
172.16.10.0, broadcast is 172.16.10.127, and
valid host range is 172.16.10.1 through 126.
You need to ask yourself,

Is the subnet bit in
the fourth octet on or off?


If the host address
has a value of less than 128 in the fourth octet,
then the subnet bit must be off. If the value of
the fourth octet is higher than 128, then the
subnet bit must be on. In this case, the host
address is 10.5, and the bit in the fourth octet
must be off. The subnet must be 172.16.10.0.

Answer q 2 and 3

2.
172.16.10.33 255.255.255.224: Subnet is
172.16.10.32, broadcast is 172.16.10.63, and
valid host range is 172.16.10.33 through 10.62.
256

224
=
32. 32
+
32
=
64

bingo. The subnet
is 10.32, and the next subnet is 10.64, so the
broadcast address must be 10.63.

3.
172.16.10.65 255.255.255.192: Subnet is
172.16.10.64, broadcast is 172.16.10.127, and
valid host range is 172.16.10.65 through
172.16.10.126. 256

192
=
64. 64
+
64
=
128, so
the network address must be 172.16.10.64, with a
broadcast of 172.16.10.127.

Answer of Q4
-
6

4.
172.16.10.17 255.255.255.252: Subnet is 172.16.10.16,
broadcast is 172.16.10.19, and valid hosts are
172.16.10.17 and 18. 256

252
=
4. 4
+
4
=
8, plus 4
=
12, plus 4
=
16, plus 4
=
20

bingo. The subnet is
172.16.10.16, and the broadcast must be 10.19.

5.
172.16.10.33 255.255.255.240: Subnet is 172.16.10.32,
broadcast is 172.16.10.47, and valid host range is
172.16.10.33 through 46. 256

240
=
16. 16
+
16
=
32,
plus 16
=
48. Subnet is 172.16.10.32; broadcast is
172.16.10.47.

6.
192.168.100.25 255.255.255.252: Subnet is
192.168.100.24, broadcast is 192.168.100.27, and
valid hosts are 192.168.100.25 and 26. 256

252
=
4.
4
+
4
=
8, plus 4
=
12, plus 4
=
16, plus 4
=
20, plus 4
=
24, plus 4
=
28. Subnet is 100.24; broadcast is 100.27.


Answer of Q7
-
8

7.
192.168.100.17, with 4 bits of subnetting:
Subnet is 192.168.100.16, broadcast is
192.168.100.31, and valid host range is
192.168.100.17 through 30. 256

240
=
16.
16
+
16
=
32. Subnet is, then, 100.16, with a
broadcast of 100.31 because 32 is the next
subnet.

8.
192.168.100.66, with 3 bits of subnetting:
Subnet is 192.168.100.64, broadcast is
192.168.100.95, and valid host range is
192.168.100.65 through 94. 256

224
=
32.
32
+
32
=
64, plus 32
=
96. Subnet is 100.64,
and broadcast is 100.95.

Question

Any question?



If you do not have question, please
search internet and collect more
information of router and its
manufacturers.

1.
Please be comfortable to introduce
routing protocols.

2.
Please be familiar with subnet
calculation.