The Presentation contains slides describing the details of IPv4 Header Format

1. IPv4 Header
Deconstruction
Pouyan Zamani

2. Sample Packet

3. Version

4. IHL (Internet Header Length) * 4 =in
bytes

5. ToS (Type of Service)

6. ToS (Type of Service)
• 1000: Minimize delay
• 0100: Maximize throughput
• 0010: Maximize reliability
• 0001: Minimize monetary
cost
• 0000: Normal service
• RFC 1349 > Obsolete!
• 11: Congestion Experienced
• 10: ECN Aware
• 01: ECN Aware
• 00: No ECN
• RFC 3168 > Newer!

7. ToS (Type of Service)

8. IP Datagram Length (Total Length)

9. IP ID (Identification)

10. Flags (3 bit)

11. Flags (3 bit)
• DF (Do not Fragment) :
• 0 means allow
fragmentation;
• 1 means do not allow
fragmentation.
0 :
Reserved, must be
zero.
• MF (More Fragments) :
• 0 means that this is the
last fragment of the
datagram;
• 1 means that additional
fragments will follow.

12. Fragmentation Offset (13 bit) * 8 = in
bytes

13. Fragmentation

14. Fragmentation

15. Fragmentation

16. Fragmentation

17. Fragmentation

18. Fragmentation

19. Fragmentation

20. Fragmentation

21. Questions About Fragments

22. Questions About Fragments

23. Questions About Fragments

24. IDS/IPS Challenges for
Fragmentation

25. Ping of Death

26. Teardrop

27. TTL (Time to Live)

28. Protocol

29. Protocol (https://www.eit.lth.se/ppplab/IPHeader.htm#Protocol)
Protocol Description
0 Reserved
1 Internet Control Message Protocol (ICMP)
2 Internet Group Management Protocol (IGMP)
3 Gateway-to-Gateway Protocol (GGP)
4 IP (IP encapsulation)
5 Stream
6 Transmission Control Protocol (TCP)
8 Exterior Gateway Protocol (EGP)
9 Private Interior Routing Protocol
17 User Datagram Protocol (UDP)

30. Header Checksum

31. Header Checksum
• 4500 0073 0000 4000 4011 b861 c0a8 0001
c0a8 00c7 0035 e97c 005f 279f 1e4b 8180
• 4500 + 0073 + 0000 + 4000 + 4011 + c0a8 + 0001 + c0a8 +
00c7 = 2479C
• 2 + 479C = 479E (if another carry is generated by this addition,
another 1 must be added to the sum)
• 479E > 1st complement (Binary) = B861

32. Header Checksum

33. Source IP

34. Destination IP

35. IP Options