Question:medium

Consider a network that uses Ethernet and IPv4. Assume that IPv4 headers do not use any options field. Each Ethernet frame can carry a maximum of 1500 bytes in its data field. A UDP segment is transmitted. The payload (data) in the UDP segment is 7488 bytes. Which ONE of the following choices has the CORRECT total number of fragments transmitted and the size of the last fragment including IPv4 header?

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Remember: Max IP data per Ethernet frame = 1500 – 20 = 1480 bytes, and fragment size must be a multiple of 8 bytes.
Updated On: Feb 9, 2026
  • 5 fragments, 1488 bytes
  • 6 fragments, 88 bytes
  • 6 fragments, 108 bytes
  • 6 fragments, 116 bytes
Show Solution

The Correct Option is D

Solution and Explanation

Step 1: Find the size of the original IP packet. 
The UDP payload is $7488$ bytes, and the UDP header adds another $8$ bytes.
So, the total data handed over to IP is:

\[ 7488 + 8 = 7496 \text{ bytes} \]

Since the IPv4 header has no options, its size is $20$ bytes.
Therefore, the total size of the original IP datagram becomes:

\[ 7496 + 20 = 7516 \text{ bytes} \]

Step 2: Determine how much data each fragment can carry.
The maximum transmission unit (MTU) of Ethernet is $1500$ bytes, which includes both IP header and data.
After accounting for the IP header, the usable data per fragment is:

\[ 1500 - 20 = 1480 \text{ bytes} \]

This value is suitable for fragmentation since it is a multiple of 8, as required by IPv4.

Step 3: Calculate the number of fragments.
The total IP data that must be fragmented is $7496$ bytes.
The number of complete fragments is:

\[ \left\lfloor \frac{7496}{1480} \right\rfloor = 5 \]

The remaining data for the final fragment is:

\[ 7496 - (5 \times 1480) = 96 \text{ bytes} \]

Thus, the total number of fragments formed is:

\[ 5 + 1 = 6 \]

Step 4: Find the size of the last fragment.
The last fragment carries only $96$ bytes of data.
Including the IP header, its total size is:

\[ 96 + 20 = 116 \text{ bytes} \]

Step 5: Match with the given choices.
Options with fewer than 6 fragments are incorrect.
Options with an incorrect final fragment size do not match the calculation.
The only consistent choice is the one stating 6 fragments with the last fragment size of 116 bytes.

Step 6: Final conclusion.
The correct result is:

\[ \boxed{\text{6 fragments, last fragment size } = 116 \text{ bytes}} \]

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