IT2050 - Computer Networks Lecture 5

Questions and Answers

What is the range of byte numbers for Fragment 3?

5920 to 5999

2960 to 4439 (correct)

4440 to 5919

1480 to 2959

What is the offset value for Fragment 2?

185 (correct)

555

370

What happens to fragmented packets as they travel to their destination?

They combine into a larger packet.

They travel through the same route.

They may travel through different routes. (correct)

They are defragmented during transmission.

How are fragmented packets reassembled at the destination?

Using the OFFSET values. Signup and view all the answers

Which of the following statements about the Time To Live (TTL) is correct?

TTL decreases with each router it passes. Signup and view all the answers

What can occur if there is a problem in a routing table?

Packets can be sent in the wrong direction. Signup and view all the answers

What is the offset value of the last fragment (Fragment 5)?

740 Signup and view all the answers

What indicates that fragmented packets may arrive out of order?

They travel independently. Signup and view all the answers

What makes IP an unreliable protocol?

It does not reorder packets at the destination. Signup and view all the answers

What is the purpose of the 'Identification' field in an IP packet?

To allow the receiver to reassemble packets correctly. Signup and view all the answers

If an original IP packet has 6000 bytes of data, what must be done if it exceeds the Maximum Transmission Unit (MTU)?

It must be fragmented into smaller packets. Signup and view all the answers

What is the significance of the 'Fragmentation offset' in an IP packet?

It identifies the order of fragments. Signup and view all the answers

In the context of IP, what does the acronym MTU stand for?

Maximum Transmission Unit. Signup and view all the answers

How do IP packets originating from the same source reach their destination?

They can take different routes and arrive at different times. Signup and view all the answers

What happens to the identification number of fragmented packets?

All fragments retain the same identification number as the original packet. Signup and view all the answers

Which of the following statements about TCP/IP and UDP/IP is true?

TCP/IP is reliable while UDP/IP is unreliable. Signup and view all the answers

What is the maximum value for the Time To Live (TTL) parameter in an IP packet?

255 Signup and view all the answers

What happens to an IP packet when its TTL value reaches zero at a router?

The packet is discarded and an ICMP message is sent back. Signup and view all the answers

How is the TTL value affected as an IP packet travels through routers?

It is decremented by 1 at each router. Signup and view all the answers

How can the header length (HLEN) of an IP packet be calculated?

Header size in bytes = HLEN x 4. Signup and view all the answers

What value would HLEN be if the standard header size is 20 bytes?

5 Signup and view all the answers

What is the purpose of the Precedence field in the Service Type of an IP packet?

It defines the priority of the packet. Signup and view all the answers

Which two IP versions are represented in the Version (VER) field of an IP packet?

IPv4 and IPv6 Signup and view all the answers

If a packet loops through routers multiple times, what mechanism prevents it from circulating indefinitely?

The TTL value is decremented until it reaches zero. Signup and view all the answers

What happens if a packet is discarded by a router due to TTL reaching zero?

An error message is sent back to the transmitting router. Signup and view all the answers

How many bits are used to represent the Version (VER) field in the IP header?

4 bits Signup and view all the answers

What does the total length field in an IP packet indicate?

The combined length of data and header Signup and view all the answers

Which field determines if an IP packet can be fragmented?

Flags Signup and view all the answers

How is the Fragmentation Offset field expressed?

As a 13-bit number Signup and view all the answers

What is the maximum number of hops defined by the Time To Live (TTL) field?

An 8-bit value indicating maximum hops Signup and view all the answers

Which protocol types can be identified by the protocol field in an IP packet?

UDP, TCP, ICMP, IGMP, EGP Signup and view all the answers

What does the Identification field in an IP packet signify?

The serial number for the IP packet Signup and view all the answers

What happens if errors are found in the header of an IP packet during checksum verification?

The whole IP packet is discarded Signup and view all the answers

What does the Destination IP Address field store?

The IP address of the receiving device Signup and view all the answers

Study Notes

Overview of IP

IP serves as the network layer protocol within the TCP/IP suite.
Lacks error control, flow control, and congestion control, making IP an unreliable protocol.
Combination of TCP with IP ensures reliability, whereas the UDP with IP remains unreliable.
IP packets function as datagrams, potentially taking different routes and arriving out of order.

Identification

Each IP packet has a unique serial number called "Identification."
This number aids in the correct reassembly of packets at the receiver's end, despite possible out-of-order arrival.

Maximum Transmission Unit (MTU)

Defines the maximum amount of data that can be accommodated within a frame.

Fragmentation

IP packets larger than the MTU need to be fragmented.
The fragmentation process involves separating the data from the header, breaking data into MTUs, and adding a 20-byte header to each fragment.

Fragmentation Offset

Each fragmented IP packet retains the original packet's identification number.
Offset values are crucial for ordering fragments, as displayed by the byte range examples.

Time To Live (TTL)

TTL prevents packets from circulating indefinitely in the network.
Set by the transmitting router and decremented by each router it passes through.
If TTL reaches zero, the packet is discarded, and an ICMP message is sent back to the source.

IP Header Structure

The header consists of multiple fields, each serving different purposes, such as:
- Version: Indicating the IP version used (IPv4 or IPv6).
- Header Length (HLEN): Indicates the number of 4-byte units in the header.
- Service Type: Defines the priority and type of service for the packet.
- Total Length: The combined length of the header and data.
- Identification, Flags, Fragmentation Offset: Manage packet fragmentation and reassembly.
- Time To Live (TTL): Defines maximum hops allowed.
- Protocol: Indicates the type of data contained in the packet (UDP, TCP, etc.).
- Header Checksum: Validates header integrity; errors lead to packet discard.
- Source IP Address: 32-bit field containing the sender's IP.
- Destination IP Address: 32-bit field containing the receiver's IP.

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Description

This quiz covers Lecture 5 of the IT2050 Computer Networks course, focusing on the Internet Protocol (IP). It provides insights into the network layer protocol of TCP/IP, detailing its functionalities like the absence of error and flow control. Test your understanding of these essential networking concepts.