Questions related to IP fragmentation and reassembly: (1) Consider IP datagram a

Question

Questions related to IP fragmentation and reassembly:

(1) Consider IP datagram as illustrated in Figure 6 of RFC 791, except that the total length field is 1200. If this datagram were to traverse a local network that had a maximum transmission unit size of 500 bytes it would have to be fragmented. Assume it is fragmented into three smaller datagrams according to the algorithm presented Section 3.2 (see subsection titled ``An Example Fragmentation Procedure'') of RFC 791. With this technique, each fragment (except the last) is made the maximum allowable size. What are the values of the header length, total length, identification, flags, and fragment offset fields for all three fragment headers?

(2) Assume that the datagram fragments from the previous problem finally reach the destination host which has to reassemble them into a single datagram before passing them

Explanation / Answer

(1)

Fragment 1----                         
Header Length = 5
Total length = 500
Identification = 111
Flags = 001
Fragment offset = 0

Fragment 2----
Header Length = 5
Total length = 500
Identification = 111
Flags = 001
Fragment offset = 480

Fragment 3----
Header Length = 5
Total length = 260
Identification = 111
Flags = 000
Fragment offset = 960

2)

The last bit in the Identification filed denotes whether the fragment is last fragment(0) or more fragments are to follow(1) in a datagram. Length of the fragment is known by the total length. Fragmentation offset gives the position of the fragment in the datagram .

Related Questions

Navigate

• Browse (All)
• Browse Q
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.