The Bits and Bytes of Computer Networking - Week 3
What is a Port?
A 16-bit number that is used to direct traffic to specific services running on a networked computer
What is a Sequence number?
A 32-bit number that's used to keep track of where in a sequence of tcp segments this one is expected to be.
What is a Data offset field?
A 4-bit number that communicates how long the tcp header for this segment is
What is a firewall?
A device that blocks traffic that meets a certain criteria
What is a URG (urgent)?
A value of one here indicates that the segment is considered urgent and that the urgent pointer field has more data about this.
What does the value of one in an ACK control flag represent? - The acknowledgment number field should be examined. + There is one packet to deliver. - It is the first transmission. - There is one more packet to be transmitted.
A value of one in the ACK flag field means that the acknowledgement number field should be examined.
What is a ACK (acknowledgment)?
A value of one in this field means that the acknowledgment number field should be examined
Connection-oriented protocols protect against dropped data by forming connections and using what type of constant stream? Approvals Acknowledgements Verifiers Checks
Acknowledgements - Connection-oriented protocols protect against dropped data with a constant stream of acknowledgements.
Connection-oriented protocols protect against dropped data by forming connections and using what type of constant stream?--------- Approvals - Acknowledgments - Verifiers - Checks
Acknowledgements; Connection-oriented protocols protect against dropped data with a constant stream of acknowledgements.
What is an Ephemeral Port?
An Ephemeral Port is a communications endpoint (port) of a transport layer protocol of the Internet Protocol Suite that is used for only a short period of time for the duration of a communication session.
What is a TCP segment?
Made up of a TCP header and a data section
A device that blocks traffic that meets certain criteria is know as a ________.
- Firewall; A firewall is used to block certain defined types of traffic.
What is a Presentation layer?
Responsible for making sure the unencapsulated application layer data is able to be understood by the application in question
What port does the File Transfer Protocol (FTP) typically listen on?
21; FTP typically listens on port 21.
What is a Source port?
A high numbered port chosen from a special section of ports known as ephemeral ports
What is a handshake?
A way for two devices to ensure that they're speaking the same protocol and will be able to understand each other
An example of something that operates at the application layer is:
A web browser; Web browsers and servers operate at the application layer.
What is a RST (reset)?
One of the sides in a TCP connection hasn't been able to properly recover from a series of missing or malformed segments.
What is a TCP checksum?
Operates just like the checksum fields at the IP and Ethernet level.
How many bits are reserved for the Transmission Control Protocol (TCP) flags?
- 6; 6 bits are reserved for the 6 TCP control flags.
HTTP is an example of a(n) _______________ layer protocol.
- Application; There are lots of application layer protocols, but HTTP is one of the most common ones.
A device receives a Transmission Control Protocol (TCP) packet. The device understands where the actual data payload begins. Which portion of the TCP header provides this information?
- Data offset; The data offset field communicates how long the TCP header for a segment is. This causes the receiving network device to understand where the actual data payload begins
Ports that are generally used to establish outbound connections are known as ______________ ports.
- Ephemeral; The exact ports used are different, depending on the operating system, but they're all known as ephemeral ports.
A network has the ability to direct traffic toward all of the receiving services. What provides this ability in the transport layer?
- Multiplexing; Multiplexing in the transport layer means that nodes on a network have the ability to direct traffic toward many different receiving services.
If the transmitting device would like for the receiving device to push currently buffered data to the application on the receiving end immediately, it would set the ___________ flag.
- PSH; The PSH flag ensures that the receiving end doesn't wait for any further data.
Please select all valid TCP control flags. WAIT, URG, ACK, LISTEN, RST, CLOSE
- RST, - ACK, - URG
Ports 1 - 1023 are known as ______ ports.
- System; System ports are used for very well-known services.
The concept of taking traffic that's all aimed at the same node and delivering it to the proper receiving service is known as _________. multiplexing demultiplexing routing encapsulation
Demultiplexing allows traffic intended for many different services to be delivered to the same node.
A Transmission Control Protocol (TCP) connection is in working order and both sides can send each other data. What is the TCP socket state? SYN_RECEIVED ESTABLISHED LISTEN SYN_SENT
ESTABLISHED - The ESTABLISHED state means that the TCP connection is in working order and both sides are free to send each other data.
What is a Connection orientation protocol?
Establishes a connection and uses this to ensure that all of the data has been properly transmitted
What is a Session layer?
Facilitating the communication between actual applications and the transport layer
A device involved in a Transmission Control Protocol (TCP) connection is ready to close the connection. The other device in the connection agrees. What has occurred? Handshake Four-way handshake Two-way handshake Three-way handshake
Four-way handshake - A four-way handshake occurs when the session is closed.
What is a Options field?
It is sometimes used for more complicated flow control protocols
What is a SYN (synchronize)?
It's Used when first establishing a TCP connection and makes sure you be receiving end knows to examine the sequence number field.
If the transmitting device would like for the receiving device to push currently buffered data to the application on the receiving end immediately, it would set the ____ flag
PSH The PSH flag ensures that the receiving end doesn't wait for any further data.
You are sending a very small amount of information that you need the listening program to respond to immediately. Which Transmission Control Protocol (TCP) flag will be used?
PSH; The PSH flag will be used to push the information immediately.
Which ports are Ephemeral Ports?
Ports 49152 - 65535 are known as ephemeral ports . Another name for it is private ports . It's called so because this range of ports can't be registered with IANA.
What is the typical range of ephemeral ports?
The default ephemeral port numbers are in the range 1024 - 65535.
What is a Acknowledgment number?
The number of the next expected segment
Application layer data lives in the _____ section of the transport layer protocol. data payload header footer flags
The payload section of one layer contains the content of the layer above it.
What is a Destination Port?
The port of the service the traffic is intended for
Unlike our five-layer model, the OSI network model adds two more layers on top of the Application Layer. Select examples of these new layers below.
The presentation layer; The presentation layer might handle things like compression or encryption. The session layer; The session layer handles the delivery of data from the transport layer to applications themselves.
What is a PSH (push)?
The transmitting device wants the receiving device to push currently-buffered data to the application on the receiving end as soon as possible
A connection, at which layer, implies that every segment of data sent is acknowledged? Data link Transport Network Application
Transport layer - A connection at the transport layer implies that every segment of data sent is acknowledged. This way, both ends of the connection always know which bits of data have definitely been delivered to the other side and which haven't.
What is a Urgent pointer field?
Used in conjunction with one of the TCP control flags to point out particular segments that might be more important than others.
What is a FIN (Finish)?
When this flag is set to one, it means the transmitting computer doesn't have any more data to send and the connection can be closed
A device involved in a Transmission Control Protocol (TCP) connection is ready to close the connection. The other device in the connection agrees. What has occured?
four-way handshake; A four-way handshake occurs when the session is closed.
What's the standard number for a TTL field?
- 64; While this value can be set to anything from 0 to 255, 64 is the recommended standard.
How many bits are used to direct traffic to specific services running on a networked computer?
- 16; A port is a 16-bit number that's used to direct traffic to specific services running on a networked computer.
Transport layer protocols, like TCP and UDP, introduce the concept of a port. How many bits is a port field?
16 bits; A TCP or UDP port is a 16-bit number, meaning there are theoretically 65,535 possible values it can have.
How many bits are in the checksum field in a Transmission Control Protocol (TCP) header? 12 8 16 4
16-bit The checksum field is a 16-bit field and is used to make sure no data was lost or corrupted during transmission.
How many Transmission Control Protocol (TCP) control flags are there?
6
How many bits are reserved for the Transmission Control Protocol (TCP) flags? 10 4 8 6
6 bits are reserved for the 6 TCP control flags.
HTTP is an example of a(n) ______ layer protocol. transport data-link application network
Application There are lots of application layer protocols, but HTTP is one of the most common ones.
A device receives a Transmission Control Protocol (TCP) packet. The device understands where the actual data payload begins. Which portion of the TCP header provides this information? Checksum Data offset Acknowledgement number Sequence number
Data Offset Field - The data offset field communicates how long the TCP header for a segment is. This causes the receiving network device to understand where the actual data payload begins.
Ports 1024-49151 are known as ______ ports. - system - registered - destination - source
Registered:
Which Transmission Control Protocol (TCP) flag is used to make sure the receiving end knows how to examine the sequence number field? URG ACK PSH
SYN The SYN flag is used to make sure the receiving end knows how to examine the sequence number field.
One side in a Transmission Control Protocol (TCP) connection has not been able to properly recover from a series of malformed segments. Which Transmission Control Protocol (TCP) flag will be used? FIN SYN RST PSH
SYN flag - The SYN flag is used to make sure the receiving end knows how to examine the sequence number field.
What ordering of TCP flags makes up the Three-way Handshake?
SYN, SYN/ACK, ACK; The computer that wants to establish a connection sends a packet with the SYN flag set. Then, the server responds with a packet with both the SYN and ACK flags set. Finally, the original computer sends a packet with just the ACK flag set.
A communication sent through Transmission Control Protocol (TCP) arrives out of order. What allows the data to be put back together in the correct order? Sequence numbers Acknowledgement number Checksum Preamble
Sequence numbers - Sequence numbers allow the data to be put back together in the correct order.
What is a TCP window?
Specifies the range of sequence numbers that might be sent before and acknowledgment is required.
In which scenario should you use the User Datagram Protocol (UDP)? When you make a phone call When you are using instant messaging with a co-worker When you are sending an email When you are streaming a video
Streaming a video through a connectionless protocol, such as UDP, will require less traffic, which will provide a faster connection.
Which field in a Transmission Control Protocol (TCP) header is not typically used in modern networking? Acknowledgment Number Urgent Pointer Sequence Number Checksum 8
The Urgent Pointer field is not typically used in modern networking. This field points out particular segments that might be more important than others but is a feature of TCP that hasn't really ever been adopted.
A connection, at which layer, implies that every segment of data sent is acknowledged?
transport; A connection at the transport layer implies that every segment of data sent is acknowledged.