CCNA community: CCNA(4th class)

TCP/IP model

è Model developed by DoD(Department of Defence).

è OSI model was not developed for TCP and IP but this model solely focus on TCP/IP.

è Basically functions are same but layers are less.

Carrier Sense Multiple Access/Collision Detection(CSMA/CD)

è Listens to one for any signals.

è Jam signal is sent on collision.

è Now, sender invokes random time collapsing

è At the end of random timer, they again start listening from the wire for any data.

è If present, donot send if not start sending.

Cabling Standard

Straight Cable

è Used to connect dissimilar devices.

è Example: PC-switch, Router- switch, etc.

è A-A B-B

Cross Cable

è Used to connect similar devices

è Example: PC-PC, Switch-Switch, Router-Router, PC-router, etc.

è A-B B-A

Note:

Port with auto MDIX feature automatically detects the required cable connection type and configure the connection appropriately.

Communication:

1. Half duplex

è Either send or receive at a time

è Example: Walky Talky

2. Full duplex

è Both send and receive at the same time

è Example: Telephone

Broadcast

è One to many (all) communication

è Example: ARP broadcast

Multicast

è One to group communication

è Example: routing protocol

Unicast

è One to one communication

CISCO 3 Hierarchial model

Access layer	Where end device ends
Distribution layer	Responsible for routing, filtering, security, network policy, etc.
Core(backbone) layer	Responsible for transporting large amount of data forward the traffic as fast as possible

Collapse layer

è A layer where core and distribution layers functions together.

IPv4 addressing

- It is a 32- bit addressing scheme represented in dotted decimal format

- Consists of 4 octets each separated by periods(.)

- Example: 192. 168.1.19

Classes of IP

Class	First octet	Default subnet mask	N/H ratio
A	1-126	255.0.0.0	N.H.H.H
B	128-191	255.255.0.0	N.N.H.H
C	192-223	255.255.255.0	N.N.N.H
D	224-239	Multicast purpose
E	240-255	Reserved for experimental purpose