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network tut


tcp/ip layers

  1. Physical Layer
  2. Data Link Layer (MAC)  = ppp framing ,ethernet  IEEE 802.2 framing
  3. Network/Internet Layer(IP) = ip,icmp,arp
  4. Transport Layer(TCP/UDP)
  5. Application Layer = http/s, ntp, ssh


 OSI layers

  1. physical layer
  2. Data link layer : media access control (MAC) and logical link control (LLC).
  3. Network layer
  4. Transport layer
  5. Session layer
  6. Presentation layer
  7. Application layer


ipv4 address  length = 32 bit
ipv6 length = 128 bit

mac address length = 48 bit


c:> ipconfig /all

Physical Address(mac). . . . . . . . . : B6-97-B1-6E-AB-B1

DHCP Server(ipv4) . . . . . . . . . . . :

IPv6 Address. . . . . . . . . . . : 2400:1a00:bd20:7939::3(Preferred)

 IPv6 Address. . . . . . . . . . . :  2400:1a00:bd20:7939:3436:ce31:2aa:1607(Preferred)  

port length = 16-bit integer,

Well known Ports    0 – 1023
Registered Ports    1024 – 49151
Ephemeral Ports    49152 – 65535

assined by iana ,  On Unix-like operating systems, a process must execute with superuser privileges to be able to bind a network socket to an IP address using one of the well-known ports. On most systems, registered ports can be used without superuser privileges.

c:> netstat -a

browse using ipv6 

According to RFC2732, literal IPv6 addresses should be put inside square brackets in URLs




nslookup google.coom      

Address:  2400:1a00:0:32::165                                                                                                                Non-authoritative answer:
Addresses:  2404:6800:4002:82f::200e                                                                      


 ARP stands for Address Resolution Protocol
It is used to convert an IP address to its corresponding physical address(i.e., MAC Address). 
ARP is used by the Data Link Layer to identify the MAC address of the Receiver’s machine. 


RARP stands for Reverse Address Resolution Protocol
As the name suggests, it provides the IP address of the device given a physical address as input. But RARP has become obsolete since the time DHCP has come into the picture. 


classful addressing

  • Class A
  • Class B
  • Class C
  • Class D
  • Class E

Classes D and E are reserved for multicast and experimental purposes respectively.

 IPv4 address is divided into two parts:

  • Network ID (NID)
  • Host ID (HID)




IP addresses are globally managed by Internet Assigned Numbers Authority(IANA) and regional Internet registries(RIR).


Class A

IP address belonging to class A are assigned to the networks that contain a large number of hosts.

NID=8bit HID=24 

The higher order bit of the first octet in class A is always set to 0

The default subnet mask for class A is 255.x.x.x

2^7-2= 126 network ID(Here 2 address is subtracted because and 127.x.y.z are special address. )

2^24 – 2 = 16,777,214 host ID

 IP addresses belonging to class A ranges from 1.x.x.x – 126.x.x.x


Class B

IP address belonging to class B are assigned to the networks that ranges from medium-sized to large-sized networks.

NID=16bit HID=16

The higher order bits of the first octet of IP addresses of class B are always set to 10

The default sub-net mask for class B is 255.255.x.x.

2^14 = 16384 network address
2^16 – 2 = 65534 host address 

IP addresses belonging to class B ranges from 128.0.x.x – 191.255.x.x.


Class C

IP address belonging to class C are assigned to small-sized networks.

NID=24bit HID=8

The higher order bits of the first octet of IP addresses of class C are always set to 110.

The default sub-net mask for class C is 255.255.255.x.

    2^21 = 2097152 network address
    2^8 – 2 = 254 host address

IP addresses belonging to class C ranges from 192.0.0.x – 223.255.255.x.


class D

The higher order bits of the first octet of IP addresses belonging to class D are always set to 1110

The remaining bits are for the address that interested hosts recognize

IP addresses belonging to class D ranges from –


class E

The higher order bits of first octet of class E are always set to 1111

IP addresses of class E ranges from –


special ip range – : Link local addresses – : Loop-back addresses – : used to communicate within the current network.


host id rules

all 0  host ID is used to represent the network ID of the IP address

all 1 host ID is reserved as a broadcast address to send packets to all the hosts present on that particular network.

the host ID must be unique to the network


network id rules

 The network ID cannot start with 127 because 127 belongs to class A address and is reserved for internal loop-back functions.

all 1 is reserved for  IP broadcast address

all 0 denote a specific host on the local network and are not routed






 ipv4 header

VERSION: Version of the IP protocol (4 bits), which is 4 for IPv4

HLEN: IP header length (4 bits), which is the number of 32 bit words in the header. The minimum value for this field is 5 and the maximum is 15.

Type of service: Low Delay, High Throughput, Reliability (8 bits)

Total Length: Length of header + Data (16 bits), which has a minimum value 20 bytes and the maximum is 65,535 bytes.

Identification: Unique Packet Id for identifying the group of fragments of a single IP datagram (16 bits)

Flags: 3 flags of 1 bit each : reserved bit (must be zero), do not fragment flag, more fragments flag (same order)

Fragment Offset: Represents the number of Data Bytes ahead of the particular fragment in the particular Datagram. Specified in terms of number of 8 bytes, which has the maximum value of 65,528 bytes.

Time to live: Datagram’s lifetime (8 bits), It prevents the datagram to loop through the network by restricting the number of Hops taken by a Packet before delivering to the Destination.

Protocol: Name of the protocol to which the data is to be passed (8 bits)

Header Checksum: 16 bits header checksum for checking errors in the datagram header

Source IP address: 32 bits IP address of the sender

Destination IP address: 32 bits IP address of the receiver

Option: Optional information such as source route, record route. Used by the Network administrator to check whether a path is working or not.


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