Objective 1.1 (Compare and contrast the Open Systems Interconnection (OSI) model layers and encapsulation concepts)

TCP Flags

-total of 8 bits for 8 flags 1) CWR- congestion window reduced (rarely used) 2) ECE- ECN-echo explicit congestion notification (rarely used) 3) URG- urgent 4) ACK- acknowledgement 5) PSH- push 6) RST- reset 7) SYN- synchronize 8) FIN- finish "unskilled attackers pester real security folk"

How does a 3-way handshake work?

1. The first device (client) sends a SYN packet. *starting the conversation 2. The second device (server) sends a SYN/ACK. *Acknowledges it received the SYN 3. 1st Device (client) sends ACK *Officially starts data transfer

What is the default MTU

1500 bytes

TCP (Transmission Control Protocol)

A connection-oriented, guaranteed-delivery protocol used to send data packets between computers over a network like the Internet.

This process involves unwrapping PDUs that were sent from a device to yours

Decapsulation

Ethernet Header What parts make up the ethernet Header? In Order?

Destination MAC Address: The MAC address of the device to which the frame is being sent. Source MAC Address: The MAC address of the device sending the frame. EtherType or Length Field: Indicates either the type of payload encapsulated within the frame or the length of the data in the frame. Optional VLAN Tag: If the frame is part of a Virtual LAN (VLAN), this field contains VLAN identification information. Frame Check Sequence (FCS): A field containing a checksum or cyclic redundancy check (CRC) value, used for error detection in the frame.

This process involves encasing different PDUs as it travels from a one device to another.

Encapsulation

What section of the UDP Header lets the segment know where to go?

Source Port: A 16-bit field indicating the port number of the sending application. Destination Port: A 16-bit field indicating the port number of the receiving application.

What section of the TCP Header lets the segment know where to go?

Source Port: Specifies the source port number, identifying the sending application on the local host. Destination Port: Specifies the destination port number, identifying the receiving application on the remote host.

What is a IP header? What parts of the IP header let the packet know where to go?

The IP header is a fundamental component of an IP packet, containing essential information for the routing and delivery of data across IP networks. Source IP address Destination IP address

Layer 7 - Application Layer

The highest layer of the OSI model, where network services and applications interact with the network infrastructure and end-users, providing functions such as file transfer, email, web browsing, and remote access.

MTU (maximum transmission unit)

The largest IP packet size in bytes allowable by routers in a path without fragmentation and excluding the frame size.

Layer 6 - Presentation Layer

The layer responsible for data translation, encryption, compression, and formatting, ensuring that data sent by the application layer is presented in a readable format to the receiving application.

Layer 3 - Network Layer What PDU is used at this layer?

The layer responsible for logical addressing, routing, and forwarding of data packets between different networks, enabling end-to-end communication across multiple networks. PDU = Packets

Layer 4- Transport Layer What PDU is used at this layer?

The layer that ensures reliable and efficient data transfer between end systems, providing services such as segmentation, reassembly, error recovery, and flow control. PDU depends on the protocol being used TCP = Segments UDP = Datagrams

Layer 5 - Session Layer

The layer that establishes, maintains, and terminates communication sessions between applications, facilitating dialogue control and synchronization between devices.

Layer 2 - Data Link What PDU is used at this layer?

The layer that provides error-free transmission of data frames between adjacent nodes over a physical link, handling framing, error detection, and flow control. This layer is used for LAN connectivity. PDU = Frames

What happens if one device is using an MTU of 1500 bytes and another device communicating to that device has a custom MTU of 9000 bytes?

The slowest MTU becomes the MTU of all the packets

What transport protocol would most suitable for a voice/video calls?

UDP (User Datagram Protocol)

What is fragmentation?

When packets are too and are chopped into smaller pieces

UDP (User Datagram Protocol)

connectionless protocol that does not require a connection to send a packet and does not guarantee that the packet arrives at its destination

Layer 1 - Physical layer What PDU is used at this layer?

physical and electrical medium for data transfer, includes but is not limited to cables, jacks, patch pannels, punch blocks, hubs, and MAUs. PDU=bits