IP packet structure in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

📋 Factual

intermediate

Identify the correct size of the IP header without options

What is the size in bytes of a standard IPv4 header without any options included?

A 40 bytes

B 24 bytes

C 32 bytes

D 20 bytes

💡 Hint

Think about the minimum fixed length of the IPv4 header fields.

The standard IPv4 header without options is always 20 bytes long. Options, if present, increase this size.

🧠 Conceptual

intermediate

Purpose of the Time To Live (TTL) field in an IP packet

What is the main purpose of the Time To Live (TTL) field in an IPv4 packet header?

A To indicate the packet's priority level for routing

B To specify the maximum number of hops a packet can take before being discarded

C To identify the source IP address of the packet

D To specify the total length of the IP packet

💡 Hint

Consider how networks prevent packets from circulating endlessly.

The TTL field limits how many routers (hops) a packet can pass through. Each router decreases TTL by one. When TTL reaches zero, the packet is discarded to avoid infinite loops.

🔍 Analysis

advanced

Determining the payload size from IP header fields

Given an IPv4 packet with a Total Length field value of 60 bytes and an Internet Header Length (IHL) of 5, what is the size of the payload (data) in bytes?

A 40 bytes

B 20 bytes

C 60 bytes

D 80 bytes

💡 Hint

Remember that IHL is measured in 32-bit words and Total Length includes header and data.

IHL of 5 means header length is 5 × 4 = 20 bytes. Total Length is 60 bytes, so payload = 60 - 20 = 40 bytes.

❓ Comparison

advanced

Difference between IPv4 and IPv6 header sizes

Which statement correctly compares the header sizes of IPv4 and IPv6 packets?

A IPv4 header is variable length, minimum 20 bytes; IPv6 header is fixed length of 40 bytes

B IPv4 header is fixed length of 40 bytes; IPv6 header is variable length, minimum 20 bytes

C Both IPv4 and IPv6 headers have fixed length of 20 bytes

D Both IPv4 and IPv6 headers have variable length depending on options

💡 Hint

Consider how options affect header length in IPv4 and IPv6.

IPv4 headers can vary in length due to optional fields, starting at 20 bytes minimum. IPv6 headers have a fixed length of 40 bytes, with extension headers handled separately.

❓ Reasoning

expert

Effect of incorrect checksum in IP header

What happens when an IPv4 packet arrives at a router with an incorrect header checksum?

A The router sends the packet back to the sender

B The router corrects the checksum and forwards the packet

C The router discards the packet and does not forward it

D The router forwards the packet without checking the checksum

💡 Hint

Think about how routers ensure data integrity before forwarding.

Routers verify the header checksum to detect errors. If the checksum is incorrect, the packet is considered corrupted and discarded to prevent forwarding bad data.