# Homework3

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1. Find all the Fragments and Field Values for Fragment Headers in Slide 20 of our notes.

Original Datagram (=Packet) = 404 Octets/Bytes
Offset = 0
More = 0

Fragment (Data+IP Header=Payload) Limit = 208 Bytes
With a minimum 20 bytes Header Size
• *IMPORTANT: Offset calculation is done on the Data Payload ONLY!!!
• --> Offset = Payload / 8

Original datagram payload = Data(384bytes) + Header(20bytes)

• 1st Fragment:
• Length = 208 Bytes
• Offset = 0
• More = 1

• 2nd Fragment:
• Length = 208 Bytes
• Offset = (208-20)/8 = 23.5 bytes
• More = 1

• 3rd Fragment:
• Payload = (384 - (188+188)) = 8bytes left
• = 8 + 20 = 28bytes
• Length = 28 bytes
• Offset = 8(payload) / 8 = 1
• More = 0
2. An IP Datagram of length 4326 Bytes needs to be sent on a LAN (Local Area Network) that uses CSMA/CD Protocol. How many fragments will need to be sent for this original IP Datagram? Mention all needed fields for all resulting fragments
• Original Datagram (=Packet) = 4326 Bytes
• Max Payload of Ethernet = 1500 Bytes
• Max IP packet size = 1500 = Data(1500-20 = 1480 bytes) +Header(20 bytes)

• 1st Fragment:
• Length = (1480+20) = 1500 bytes
• Offset = 0
• More = 1

• 2nd Fragment:
• Length = 1500 bytes
• Offset = (1500 - 20)/8 = 185 bytes
• More = 1

• 3rd Fragment:
• Length = 4306(original) - 1480 - 1480 = 1346bytes
• = 1346 + 20 = 1366 bytes
• Offset = 4326(original)-1346(length)=2980
• = (2980 - 20) / 8 = 370 bytes
• More = 0
3. Find the Number of Networks and Number of Hosts that can be supported by a Class A, Class B and Class C (used for unicast) IP Address Type.
• Clss | Lft Bits | NetID | HostID | #Networks | #Hosts
• A 0xxx 8 24 ~27 (-2) ~224 (-2)
• B 10xx 16 16 ~214 (-2) ~216 (-2)
• C 110x 24 8 ~221 (-2) ~28 (-2)
4. Read RFC-791, RFC-1071 and RFC-790. What are they, what is their significance?
• RFC-791 refers to the Internet Protocol (IP): Forwarding and Addressing in the Internet, focusing on IPv4. It revises aspects of addressing, error handling, option codes, and the security,
• precedence, compartments, and handling restrictions features of the Internet
• Protocol.

• RFC-1071 refers to the computing
• of Internet Checksum that is used by the standard Internet protocols IP, UDP,
• and TCP. It informs about the techniques and algorithms for efficiently
• computing the Internet Checksum, considering that the efficiency of checksum
• implementation is critical to a good performance.

• RFC-790 refers to the Assigned
• Network Numbers/Assigned Numbers. This Network Working Group Request for
• Comments documents the currently assigned values from several series of numbers
• used in network protocol implementations.

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 Author: erika01 ID: 111812 Filename: Homework3 Updated: 2011-10-24 20:47:48 Tags: Kumar CNP Folders: Description: Problems and Solutions Show Answers:

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