What is a Firewall?
A Firewall is used to protect unauthorised access to a computer or a computer network.
The firewall does this by sitting between the external network (e.g. the Internet) and the internal network or computer that it is protecting by filtering the packets sent to or from a network.
Open System Interconnect (OSI) Firewall Model
The Open Systems Interconnect model is conceptual and was created to characterise and standardise the architecture that provides communication of a telecommunication system or a computer or network and is the standard for communication protocols.
The OSI model was developed during the late 1970s in order to support the different types of computer networking methods that were appearing nationally within the United States, France and the United Kingdom
During the 1980s, the model was produced by the Open Systems Interconnection Group at the International Organisation for Standardisation (ISO).
The Open Systems Interconnect model provides 7 layers that are summarised below:
Physical – Layer 1
This layer defines the physical network including the cabling, connectors, interface, and the network topology.
Data Link – Layer 2
The Data Link Layer connected the physical layer to the data layer and allows data to be transmitted across the network.
The Data Link Layer is split into 2 sublayers, being the Logical Link Control Sublayer and the Media Access Control Sublayer.
The Logical Link Control Sublayer determines which mechanisms are used for controlling the data that is exchanged and controls the synchronisation, flow rate and error check functions of the data link.
The Media Access Control Sublayer (MAC address) is a 12 digit unique address that is programmed into the network controller and provides access to the network hardware.
Network – Layer 3
The Network Layer manages the best path for data to be transferred by assigning the source and destination IP addresses.
Transport – Layer 4
The Transport Layer carries the data across the network from the source to the destination host using:
i. Segmentation – breaks the data down into more manageable blocks so that the connection and network can handle it;
ii. Service Addressing – Ensures that any data sent is passed to the correct service and to the correct port;
iii. Error Checking – Verifies that the data that has been sent or received was correct.
The transport layer also handles the flow control of data which determines how that data is received. The layer does this through Buffering, where data is temporarily stored within a buffer and waits for the recipient to be able to receive it, and through Windowing, where data is grouped together within agreed blocks when the connection is made.
Session Layer – Layer 5
The Session Layer makes, maintains and ends the connection between the devices and is responsible for the transfer of data.
Presentation – Layer 6
The Presentation Layer converts the data from the application layer into a format that can be transferred across a network. This is also the layer where the encryption and decryption of data is completed.
Application – Layer 7
The top of the OSI model is the application layer that accepts data from the user and passed to the other layers of the model for transmission and where the data responses are then passed and displayed to the user.
About Athena Forensics
For information on our digital forensic services or if you require any advice or assistance please contact a member of our team on 0330 123 4448 or via email on email@example.com, further details are available on our contact us page.
Our client’s confidentiality is of the utmost importance. All correspondence is treated with discretion, from initial contact to the conclusion of any computer forensic investigation.
Our digital forensics experts are fully aware of the significance and importance of the information that they encounter and we have been accredited to ISO 9001 for 10 years.
Our forensic experts are all security cleared and we offer non-disclosure agreements if required. Our premises along with our security procedures have been inspected and approved by law enforcement agencies.
Athena Forensics do not disclose personal information to other companies or suppliers.