NETWORK FUNDAMENTALS

OSI vs TCP/IP model

1.   OSI model borrows its roots from ISO whereas TCP/IP originated from research performed by DOD USA.

2.   OSI consists of 7 layers whereas TCP/IP consists of 4 layers only.

3.   OSI is a reference model whereas TCP/IP is an implementation of OSI model.

4.   When it comes to reliability, TCP/IP is most reliable than OSI.

5.   TCP/IP is protocol dependent model. On the other hand OSI is protocol independent.

6.   In OSI, data coming from the Application layer is handed over to the Presentation layer, Session layer & then to the Transport layer. But in TCP/IP, data coming from Application layer is directly handed over to the Transport layer.

TCP vs UDP protocol

1.   TCP stands for Transmission Control Protocol, UDP stands for User Datagram Protocol.

2.   TCP is connection oriented whereas UDP is connectionless protocol.

3.   TCP performs 3-way handshake. No such thing in case of UDP.

4.   TCP performs re-transmission where UDP don't perform re-transmission.

5.   TCP demands acknowledgment message whereas UDP doesn't demand acknowledgement message.

6.   TCP performs guaranteed delivery of data whereas UDP performs best effort delivery.

7.   TCP is a reliable protocol, UDP is unreliable.

8.   TCP is relatively slow. On the other hand, UDP is comparatively fast.

Impact of infrastructure components in an enterprise network

1.   Firewalls: designed to prevent unauthorized access to your network.

·     ASA (Adaptive Security Appliances): A security device that combines firewall, antivirus, intrusion prevention, and virtual private network (VPN) capabilities. It provides threat defense that stops attacks before they spread through the network.

·     NGFW (Next Generation Firewall): A next-generation firewall combines a traditional firewall with other network device filtering functionalities such as IPS (Intrusion Prevention System)

·     Next Generation Intrusion Prevention System – NGIPS

·     Firepower

2.   Access Points: allow wireless devices to connect to a wired network.  The access point itself connects to the network via a wired connection. Wireless devices connect wirelessly to the access point and can be segregated from each other.

3.   Wireless controllers:  Network admins use these to manage many different access points.  When access points are configured to pull their configuration from a wireless controller they are called lightweight access points.  A wireless controller can manage a large number of access points at once, which reduces the amount of management overhead required.

COLLAPSED CORE vs 3-TIER MODEL

Many small enterprise networks do not grow significantly larger over time. Therefore, a two-tier hierarchical design where the core and distribution layers are collapsed into one layer is often more practical. A “collapsed core” is when the distribution layer and core layer functions are implemented by a single device. The primary motivation for the collapsed core design is reducing network cost while maintaining most of the benefits of the three-tier hierarchical model.

Compare & contrast network topologies

v Star topology

Ø Advantages:

·     Due to its centralized nature, this topology offers the simplicity of operations.

·     It assures isolation of each device.

·     Modification in the network is quite easy as it can be done without affecting the entire network.

·     Due to its centralized nature, it is easy to troubleshoot the faults.

Ø Disadvantages:

·     Network operation depends upon a central device. Hence the failure of that device can cause the failure of the entire network.

·     Expansion of network totally depends upon the capacity of the central device.

·     The setup cost is too high.

v Mesh

Ø Advantages:

·     The arrangement of network nodes makes it possible to transmit data from one node to multiple nodes at the same time.

·     Failure of a single node doesn't cause failure of the entire network.

·     Can handle heavy traffic due to the presence of dedicated paths between nodes.

Ø Disadvantages:

·     A lot of cabling is required, so the setup cost is too high.

·     Due to its complexity, troubleshooting is quite difficult.

v Hybrid

·     A hybrid topology is formed by combining merits/advantages of multiple topologies.

Cabling

1.   Media can be of two types:

·     Wireless. Wireless media doesn't require any physical medium to communicate. Ex: Bluetooth, Infrared, NFC (Near Field Communication), Wi-fi, Hotspot, Satellite communications.

·     Wired:  Wired media requires physical cables to communicate.

2.   Categories of wired media;

·     Copper cable & Fiber optic cable.

·     Copper cable was subdivided into:

v Co-axial cable & Twisted pair cables

·     Twisted pair cable was further divided into two types:

v STP (Shielded Twisted Pair)

v UTP (Unshielded Twisted Pair)

v NOTE: There is no such difference between STP & UTP. There is one extra layer of coating in STP as compared to UTP.

3.   STP & UTP can be further classified into:

·     Straight cable: used to connect different NIC class devices.

·     Cross-over cable: used to connect different NIC class devices.

·     Roll-over cable: used only for configuration purpose not for data transfer.

4.   Color coding scheme: There are various color coding scheme for different cable types.

·     T568B standard: Color coding is as such:

§  Pin1 White Orange

§  Pin 2 Orange

§  Pin 3 White Green

§  Pin 4 Blue

§  Pin 5 White Blue

§  Pin 6 Green

§  Pin 7 White Brown

§  Pin 8 Brown

·     T568A standard: Color coding is as such:

·     Pin1 White Green

·     Pin 2 Green

·     Pin 3 White Orange

·     Pin 4 Blue

·     Pin 5 White Blue

·     Pin 6 Orange

·     Pin 7 White Brown

·     Pin 8 Brown

5.   In Straight cable, both end follows T568B standard.

6.   In Cross cable, one end follows T568B standard while other end follows T568A standard.

7.   In Roll-over cable, one end follows T568B standard while on other end, color coding scheme is as such:

·     Pin 1 Brown

·     Pin 2 White Brown

·     Pin 3 Green

·     Pin 4 White Blue

·     Pin 5 Blue

·     Pin 6 White Green

·     Pin 7 Orange

·     Pin 8 White Orange

8.   Ethernet connectors: Commonly used connectors are RJ 11, RJ 45.

OSI LAYER FUNCTIONS & PROTOCOLS

1.   Physical Layer: Concerned with receiving and sending raw bit data over a physical medium in the form of electrical signals. Protocols used are:

·     Digital Subscriber Line

·     Integrated Services Digital Network

·     Universal Serial Bus

·     Bluetooth

·     Ethernet

2.   Data Link Layer: Link establishment and termination, frame sequencing, receives/provides frame acknowledgement, error checking, flow control. Protocols used are:

·     CDP (Cisco Discovery Protocol)

·     ARP (Address Resolution Protocol)

·     VLAN (Virtual Local Area Network)

·     VTP (VLAN Trunking Protocol)

·     DTP (Dynamic Trunking Protocol)

·     PPP (Point to Point Protocol)

·     LLDP (Link Layer Discovery Protocol)

·     STP (Spanning Tree Protocol)

·     Frame Relay

·     LACP (Link Aggregation Control Protocol)

·     PAP (Port Aggregation Protocol)

·     NDP (Neighbor Discovery Protocol)

3.   Network Layer: It provide best physical path to the data to reach its destination, to perform routing. Protocols used are:

·     IP (Internet Protocol)

·     IPSec (Internet Protocol Security)

·     IPv4, IPv6

·     ICMP (Internet Control Management Protocol)

·     IGMP (Internet Group Management Protocol)

·     IGRP (Interior Gateway Routing Protocol)

·     EIGRP (Enhanced Interior Gateway Routing Protocol)

·     RIP (Routing Information Protocol)

·     IS-IS (Intermediate System to Intermediate System)

·     OSPF (Open Shortest Path First)

·     BGP (Border Gateway Protocol)

4.   Transport Layer: Segmentation, Sequencing. Ensures end to end delivery of data. Protocols used are:

·     TCP (Transmission Control Protocol)

·     UDP (User Datagram Protocol)

·     GRE (Generic Routing Encapsulation)

5.   Session Layer: Create, maintain & terminate the session, Encapsulation.

6.   Presentation Layer: This layer converts different forms of data into a single form, Encryption, Compression, Encoding. Protocols used are:

·     SSL (Secure Socket Layer)

·     TLS (Transport Layer Security) both are cryptographic protocols.

7.   Application Layer: This layer provides a user interface so that user can access network services. Protocols used are:

·     DNS (Domain Name System)

·     DHCP (Dynamic Host Configuration Protocol)

·     FTP (File Transfer Protocol)

·     HTTP (Hypertext Transfer Protocol), HTPs

·     NTP (Network Time Protocol)

·     TFTP (Trivial File Transfer Protocol)

·     SFTP (Secure File Transfer Protocol)

·     SSH (Secure Shell)

·     Telnet

·     SNMP (Simple Network Management Protocol)

·     SMTP (Simple Mail Transfer Protocol)

LIST OF PORT NUMBERS

Ø 20/21 FTP (TCP)

Ø 22 SSH (TCP)

Ø 23 TELNET (TCP)

Ø 25 SMTP (TCP)

Ø 53 DNS (TCP/UDP)

Ø 67/68 DHCP (UDP)

Ø 69 TFTP (UDP)

Ø 80 HTTP (TCP)

Ø 110 POP3 (TCP)

Ø 115 SFTP (TCP)

Ø 123 NTP (UDP)

Ø 161 SNMP (TCP/UDP)

Ø 179 BGP (TCP)

Ø 443 HTTPS (TCP)

Ø 520 RIP (UDP)

IP BASICS

1.   The IP address is a 32-bit field divided into 4 octets.

2.   Each octet is of 8-bits.

3.   Minimum possible value of each octet is 0 in binary.

4.   Maximum possible value of each octet is 1 in binary.

5.   Minimum possible value of each octet is 0(00000000) in decimal.

6.   Maximum possible value of each octet is 255(11111111) in decimal.

7.   The IP address is divided into 5 classes:

·     Class A (1-126)      Unicast range

·     Class B (128-191)   Unicast range

·     Class C (192-223)   Unicast range

·     Class D (224-239)  Multicast range

·     Class E (240-255)   Broadcast, R&D purpose

·     NOTE: 0 & 127 have been reserved for some special purpose. 127 range has been reserved for loopback purpose.

8.   Private IP range:

·     Class A (10.0.0.0 – 10.255.255.255)

·     Class B (172.16.0.0. – 172.31.255.255)

·     Class C (192.168.0.0. – 192.168.255.255)

9.   IPv4 address type;

·     Unicast: one to one communication.

·     Multicast: one to many but not all communication.

·     Broadcast: one to all communication.