02 - Basic Networking

Network Topologies

A review of networking technologies is helpful and an important part of understanding the attacks and defenses. Network topologies represent the physical side of the network, and they form part of the foundation of our overall system. The physical layout of a network relates directly to the wiring and cabling that connects devices. Some of the common layouts we’ll cover are the bus, ring, star, mesh, and hybrid topologies.

Bus - A bus network is a network topology in which nodes are directly connected to a common linear (or branched) half-duplex link called a bus. The bus is the common link to all devices and cables. The downside to its simplicity is its vulnerability, all connectivity is lost if the bus backbone is damaged.


Ring - A ring network is a network topology in which each node connects to exactly two other nodes, forming a single continuous pathway for signals through each node.some ring layouts use a concentric circle design to provide redundancy if one ring fails.
Star - Alternatively referred to as a star network, star topology is one of the most common network setups. In this configuration, every node connects to a central network device, like a hub, switch, or computer. The central network device acts as a server and the peripheral devices act as clients. The Disadvantage is that if the hub or switch joining everything together fails, then the network will fail.


Mesh - A mesh network is a local network topology in which the infrastructure nodes connect directly, dynamically and non-hierarchically to as many other nodes as possible and cooperate with one another to efficiently route data from/to clients. The largest network in the world, the Internet, which was designed to survive a nuclear attack, is built as one large mesh network.

Hybrid - A hybrid topology is a type of network topology that uses two or more differing network topologies. These topologies include a mix of bus topology, mesh topology, ring topology, star topology, and tree topology. It takes the best of other layouts and uses them to its advantage.


OSI Model

No network discussion or network device explanation would be complete without Open Systems Interconnection (OSI) model. The Open Systems Interconnection (OSI) model defines a networking framework to implement protocols in layers, with control passed from one layer to the next. It conceptually divides computer network architecture into 7 layers in a logical progression.

 Layer 
 Function 
 Example 
Application  
Services that are used with end-user Applications.  
SMTP  
 Presentation 
Formats the data so that it can be viewed by the user Encrypt and Decrypt. 
JPG, GIF, HTTPS, SSL, TLS  
 Session 
Establishes / ends connections between two hosts  
NetBIOS , PPTP  
Transport 
Responsible for the Transport protocol and error handling  
TCP, UDP  
Network 
Reads the IP Address from the packet  
Routers, Layer 3 Switches  
 Data Link 
Reads the MAC Address from the Data Packet  
Switches  
Physical 
Send data on the Physical wire  
Hubs , NICS,Cable 

Some Well Known Ports

Port Number Service Name 
21 FTP 
22 SSH 
23 Telnet
25 SMTP 
43WhoIs 
53
DNS 
67 DHCP Server 
68 DHCP Client 
80 HTTP 
115 
SFTP 
161 SNMP 
389 LDAP
443 HTTPS 
445SMB

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