IP Subnet Table

Class A

Number of bits borrowed	Number of usable subnets	Number of usable IPs	Subnet Mask
2	4	4mt	255.192.0.0
3	8	2mt	255.224.0.0
4	16	1mt	255.240.0.0
5	32	524t	255.248.0.0
6	64	262t	255.252.0.0
7	128	131t	255.254.0.0
8	256	65,536	255.255.0.0

Class B

Number of bits borrowed	Number of usable subnets	Number of usable IPs	Subnet Mask
2	4	16,380	255.255.192.0
3	8	8,190	255.255.224.0
4	16	4,094	255.255.240.0
5	32	2,046	255.255.248.0
6	64	1,022	255.255.252.0
7	128	510	255.255.254.0
8	256	254	255.255.255.0

Class C

Number of bits borrowed	Number of usable subnets	Number of usable IPs	Subnet Mask
2	4	60	255.255.255.192
3	8	30	255.255.255.224
4	16	14	255.255.255.240
5	32	6	255.255.255.248
6	64	2	255.255.255.252

TCP/IP Subnet Table

Prefix	Subnet Mask	Number of Hosts	Networks (Class B) *	Networks (Class C) *	Inverse Mask +	Notes
/16	255.255.0.0	65534	1		0.0.255.255	Class B
/17	255.255.128.0	32766	0+1		0.0.127.255	In Class A networks, CIDR, or subnet-zero enabled networks only
/18	255.255.192.0	16382	2+1		0.0.63.255
/19	255.255.224.0	8190	6+1		0.0.31.255
/20	255.255.240.0	4090	14+1		0.0.15.255
/21	255.255.248.0	2046	30+1		0.0.7.255
/22	255.255.252.0	1022	62+1		0.0.3.255
/23	255.255.254.0	510	126+1		0.0.1.255
/24	255.255.255.0	254	254+1	1	0.0.0.255	Class C
/25	255.255.255.128	126	510+1	0+1	0.0.0.127	in class B or larger networks, CIDR, or subnet-zero enabled networks only
/26	255.255.255.192	62	1022+1	2+1	0.0.0.63
/27	255.255.255.224	30	2046+1	6+1	0.0.0.31
/28	255.255.255.240	14	4090+1	14+1	0.0.0.15
/29	255.255.255.248	6	8190+1	30+1	0.0.0.7
/30	255.255.255.252	2	16382+1	62+1	0.0.0.3
/31	255.255.255.254	0				Invalid mask since it leaves no host bits
/32	255.255.255.255	1			0.0.0.0	Special single host mask

www.mindflip.com

OSI Diagram

OSI Network Architecture

Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary architectural model for inter-computing and inter-networking communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, dividing the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained, so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.

The specific description for each layer is as follows:

Layer 7: Application Layer

• Defines interface-to-user processes for communication and data transfer in network
• Provides standardized services such as virtual terminal, file and job transfer and operations

Layer 6: Presentation Layer

• Masks the differences of data formats between dissimilar systems
• Specifies architecture-independent data transfer format
• Encodes and decodes data; encrypts and decrypts data; compresses and decompresses data

Layer 5: Session Layer

• Manages user sessions and dialogues
• Controls establishment and termination of logic links between users
• Reports upper layer errors

Layer 4: Transport Layer

• Manages end-to-end message delivery in network
• Provides reliable and sequential packet delivery through error recovery and flow control mechanisms
• Provides connectionless oriented packet delivery
• Device used - PC
  

Layer 3: Network Layer

• Determines how data are transferred between network devices
• Routes packets according to unique network device addresses
• Provides flow and congestion control to prevent network resource depletion
• Device used - Router
  

Layer 2: Data Link Layer

• Defines procedures for operating the communication links
• Frames packets
• Detects and corrects packets transmit errors
• Device used - Bridge/Switch
  

Layer 1: Physical Layer

• Defines physical means of sending data over network devices
• Interfaces between network medium and devices
• Defines optical, electrical and mechanical characteristics
• Device used - Repeater/NIC, Hub/Tranceiver
  

www.networkdictionary.com

Rollover Cable

Rollover cable (also known as Cisco console cable) is a type of null-modem cable that is most commonly used to connect a computer terminal to a router's console port. This cable is typically flat (and has a light blue color) to help distinguish it from other types of network cabling. It gets the name rollover because the pinouts on one end are literally rolled over when RJ45 plugs are used at both ends.

www.wikipedia.org

Devices can be connected by Roll-over:

Console port to Switch

Console port to Router

Cross Over Cable

Crossover Cable

Crossover cable that maps all output signals on one electrical connector to the input signals on the other connector, allowing two electronic devices to perform full-duplex communication. Most commonly, the term refers to the Ethernet crossover cable, but other cables follow the same principle. It also allows devices to communicate without a switch, hub, or router. Cross-Over cables are used to connect two computers directly through NICs without the use of a Hub or Switch or to uplink two or more hubs, switches or routers. The Pins of the RJ-45 Connectors at both ends of a cross-over cable are connected as follows:

Pin 1 ----------- Pin 3
Pin 2 ----------- Pin 6

www.wikipedia.org

Crossover used to connect same devices.

Devices can be connected by Crossover:

PC to PC

Router to Router

Switch to Switch

Hub to Hub

PC to Router