1. Lesson 4
IPv4&v6, The
IP Packets
their Headers

2. Lesson Objectives Structure of an IPv6 packet IPv4 header IPv6 header
IPv6 extension headers
IPv6 MTU
Upper layer checksums

3. IPv4與IPv6 封包結構

4. IPv6 vs. IPv4 Packet structure (IP封包結構)
maximum
65535 octets
minimum
20 octets
Upto
40 octets
payload
Option
Header
Transport-level PDU
IPv4 Header
Data Field
IHL (Header length)
payload Maximum
65535 octets
這是 IPv4 和 IPv6 PDU 之比較圖示, IPv4 和 IPv6 PDU之最大長度皆為 octets, 其中 IPv4 packet header 之長度最少為 20 octets, 而 IPv6 packet header 則固定為 40 octets, 但其後接有 0 個或 0 個以上之 Extension header.
Fixed
40 octets
0 or more
IPv6 Header
Extension
Header
Extension
Header
Transport-level PDU
IPv6 PDU

6. IPv4 vs. IPv6 Header IPv4 Packet Header IPv6 Packet Header
Service
Type
Traffic Class
Ver IHL
Total Length
Ver
Flow Label
Next Header
Hop Limit
Identification
Flags
Offset
Payload Length
TTL
Protocol
Header Checksum
Source Address
Source Address
Destination Address
Options + Padding
這是 IPv4 和 IPv6 packet Header 之比較圖示, 其中 IPv4 之 Source 及 Destination address 皆為 32 bits, 而 IPv6 則皆為 128 bits, 且 IPv4 packet header 之長度為變數 (最少為 20 bytes), IPv6 packet header 則固定為 40 bytes, 原因在於 IPv6 header 有 Options + Padding 之變動長度欄位, 而 IPv6 則將之移至後續之 Extension header 內了 .
32 bits
Destination Address

7. Header Options (0~40 bytes)
IPv4 Packet Header
Ver
IHL
Service Type
Total Length
Identification
Flags
Offset
TTL
Protocol
Header Checksum
Source Address
Destination Address
Header Options (0~40 bytes)

8. IPv4表頭結構及選項Option

9. Structure of the IPv4 Header
Version
Internet Header Length
Type of Service
Total Length
Identification
Flags
Fragment Offset
Time to Live
Protocol
Header Checksum
Source Address
Destination Address
Options
(5 to 15-4 byte as a unit~ 5*4 to 15*4)
(three bits Precedence + TOS bits)
(~65536 bytes)
Flags:XDM 3bits: D=1means must not Fragment, M=1 not the last frag. M=0, means is the last.
(1, ICMP, 2, IGMP, 6,TCP, 17 UDP, 89, OSPF)
. . .

10. Type of Service D T R C
Type of Service: 8 bits, how the datagram should be handled by the routers
This field is divided into 2 subfields: precedence (3 bits ) and TOS service type (4 bits)
Precedence is a 3-bit subfield ranging from 0 to 7, defines the priority of the datagram.
TOS bits is a 4-bit subfield, each bit having a special meaning. D: minimize delay,
T: Maximize throyghput, R: maximize the reliability, C: minimize cost.
Application programs can request a specific type of service. However, the defaults
for some applications: e.g., TELNET, minimize delay, FTP (data) Max. throught,
FTP(control) minimize delay, SMTP(control) minimize delay, ,…

11. 練習:
What is the length of the data field given an IHL value of 12 and total length value of 40000?
The IP header size?
A best-effort delivery service such as IP does not include: a) error checking, b) error correction, c) datagram acknowledgement, d) all of the above.
The checksum in the IP packet covers: a) just the header, b) just the data, c) the header and the data.
An IP datagram has arrived with the following information in the header (in hexadecimal): C 4E B4 0E 0F 02 a. Are there any options? b.Is the packet fragmented? c.What is the size of the data? d.Is a checksum used? e. How many more routers can the packet travel to? f.what is the type of service?
What is the max. number of IP address recorded if the value of the length field in the record route option is 27?

12. 問題 電腦甲欲送IP封包到電腦乙 over Ethernet: 請問 整個IP 封包，經幾次Ethernet傳送?
第二次Ethernet傳送時，之MAC frame之欄位值 內容為何?
所有Ethernet傳送中，整個IP 封包表頭，表頭之欄位值 內容為何?

13. Checksum: data integrity check:
The packet is divided into k sections, each of n bits. (n=16)
All sections are added together using one’s complement arithmetic. (checksum with zeros filled)
The final result is complemented to make the checksum.
Question: Compare with parity check which is better?

14. IP Packet Example with checksum
For Example; (For the following IP header without option) 4 5 1 28 17

15. Fragmentation in IPv4 protocol MTU Hyperchannel 65,535
IP datagram
Header
MTU in a frame
Trailer
Fields related to fragmentation (router to host)
Identification: source host mark this fields
Flags: three bits, xDM,
x: reserved
D: don’t fragment bit stands for don’t fragment ,
0 can if necessary.
M: stands for more fragments, means the datagram is not the last,
0 means the last or only fragment.
fragmentation offset: 13-bit shows the relative position of this fragment.
protocol
MTU
Hyperchannel
65,535
Token ring (16Mbps)
17,914
Token ring (4Mbps)
4,464
FDDI
4,352
Ethernet
1,500
X.25
576
PPP
296 (1500)

16. Fragmentation example
Offset = 0000/8 =0
Byte 0000
Byte 1399
Offset = 0000/8 =0
Offset = 1400/8 =175
Byte 0000
Byte 3999
Byte 1400
Byte 2799
Offset = 2800/8 =350
Assume:
MTU equals 1420 bytes
The value of offset is measured in units of eight bytes
Byte 2800
Byte 3999

17. fragment example (without considering options and upper layer header)
????
??? ?
14567
4020
000 SA DA
Fragment 1
?????
??? ?
Byte 0000~3,999
Fragment 2
?????
??? ?
Original datagram
(total 4020 bytes)
Fragment 3

18. Detailed IP fragment Byte 0000~3,999 Original datagram 14567 1420 000
820
175 1
14567
4020
000
Fragment 1
14567
1420
175 1
Fragment 2.1
14567
620
275 1
Byte 0000~3,999
Fragment 2
14567
1220
350
Original datagram
Fragment 2.2
Fragment 3

19. IPv4 Header Option (40=60-20 bytes)
Option format
Code
8 bits
Length
8 bits
Data Variable length
Number
End of Option (one byte)
No operation (one byte)
Loose source route (multiple bytes)
Timestamp (multiple bytes)
Record route (multiple bytes)
Strict source route (multiple bytes)
Copy
1 bit
Class
2 bits
Number
5 bits
Copy (when fragmented)
0 Copy only in first fragment
1 Copy into all fragments
Class
00 Datagram control
01 Reserved
10 Debugging and management
11 Reserved
Length: defines the total length of the option
including the code field and itself. (not all present)

20. Padding options No Operation: End of option:
a one-byte option used as a filler between options; coded as
End of option:
a one-byte option used for padding at the end of the option field. It can only be used as the last option. coded as if more than one byte is needed to align the option field, some no operations must be used followed by an end of option.

21. Record route concept
(code(1 byte)+length(1 byte)+pointer(1 byte)+data field)
Max. record route number :(40-4)/4, 9
Code: 1 (NOP)
Code: 7
Length
(Total length)
Pointer
First IP address (Empty when started)
Second IP address (Empty when started)
Last IP address (Empty when started)
Op: length >= pointer? If yes, stop, else put the outgoing IP address
to the field, pointed by pointer and then pointer value plus 4.

22. Strict source route concept
Dictation of a route use strict source route options as follows:
Code: 137
Length
(Total length)
Pointer
First IP address (filled when started)
Second IP address (filled when started)
Last IP address (filled when started)
Op: while (length>=pointer) to the ip address pointed by pointer, place
the outgoing IP address to the field, and then the pointer value plus 4.

23. Loose source route concept
Loose dictation of a route use loose source route options as follows:
Code: 131
Length
(Total length)
Pointer
First IP address (filled when started)
Second IP address (filled when started)
Last IP address (filled when started)
Op: Each router in the list must be visited, but the datagram can visit other
Routers as well.

24. Time Stamp Concept First IP address (filled when started) Timestamp 1
O-Flow:
Add the number of routers that could not add their timestamp due to no more fields available.
Code: 68
Length
(Total length)
O-Flow
4 bits
Pointer
Flags
4 bits
First IP address (filled when started)
Timestamp 1
Flags:
0: add for each router the timestamp
1: add the timestamp and the outgoing IP address
3: the IP address is given, each router check IP address, if match, the same operation as in flag 1.
Last IP address (filled when started)
Timestamp last

25. Practice Quiz
For an the following IP header plus Record route option :
Problem 1: What is the value of header length?
Problem 2; What is the value of check sum? 4 ?
2450 1 4 17 ?
Code: 7 15 4
First IP address (Empty when started)
Second IP address (Empty when started)
Last IP address (Empty when started)

26. In IPv4, router perform the following:
Checksum Verification [may skip it]
Verify the version
Decrement the value of TTL field.
If it is less than 1, send an ICMPv4 Time Exceeded-Time to Live to source packet, if not, place the new value in the TTL field,
Check for the presence of IPv4 header option,
Determine a forwarding interface and a next-hop IPv4 address:
Use the value of the destination address field and the contents of the local routing table to,
MTU check:
If MTU is less than the value of total length, perform IPv4 fragmentation. Recalculate the new header checksum,

27. IPv6表頭結構

28. Structure of the IPv6 Header
Destination Address
Source Address
Ver
Flow Label
Payload Length
Next Header
Hop Limit
Traffic Class
IPv6 Packet Header
Ver: 4 bits
(0110 for IPv6, 0100 for IPv4),
Traffic Class: 8 bits
with Service type in IPv4 Structure
Flow Label: 20 bits
with Label ID to attend the Qos Service
Payload length: 16 bits
length number exclude the 40 byte header.
Next Header: 8 bits
Hop Limit: 8 bits

29. Values of the Next Header Field
Hop-by-Hop Options Header 6
TCP 17
UDP 41
Encapsulated IPv6 Header 43
Routing Header 44
Fragment Header 50
Encapsulating Security Payload 51
Authentication Header 58
ICMPv6 59
No next header 60
Destination Options Header

30. Comparing the IPv4 and IPv6 Headers
IPv4 Header Field
Change in IPv6
Version
New value of 6
Internet Header Length
Removed
Type of Service
Traffic Class field
Total Length
Payload Length field
Identification
Removed to Fragment header
Fragmentation Flags
Fragment Offset
Time to Live
Hop Limit field
Protocol
Next Header field
Header Checksum
Source Address
Same, new 128-bit length
Destination Address
Options
Removed (extension headers)
增加 Flow Label 20 bits

31. In IPv6, router perform the following:
Verify the value of Version field
Decrement the value of Hop Limit Field,
if minus…send ICMPv6…, if not, place the new value
Check the next Header field for a value of 0,
if 0, process the Hop-by-Hop Options header
Use the value of Dest. Address and the contents of routing table to determine a forwarding,
If the link MTU of the forwarding is less than 40+payload, send an ICMPv6 TOO Big
Forwarding

32. IPv6 Extension Headers Hop-by-hop options header (NF=0)
40 octets
0 or more
IPv6 Header
Extension
Header
Extension
Header
Transport-level PDU
Hop-by-hop options header (NF=0)
Routing header (NF=43)
Fragment header (NF=44)
Authentication header (NF=51)
Encapsulating security payload header (NF=41)
Destination options header (NF=60)
這是 IPv6 Extension header 之示意圖, 其中 Extension header 掛在 IPv6 Header 之後, 它可以出現 0 個或0 個以上, 而它的型式有下面 6 種:
1. Hop-by-hop options header -- 定義一些需要 hop-by-hop 處理之特殊 options. Only one option is so far specified: the jumbo payload option, used to send IPv6 packets with payloads longer than 2^16 = 65,536 octets.
2. Routing header -- 提供 extended routing, 功能與 IPv4 source routing 相同,內容包括 packet 傳至 destination 所經過之一系列 nodes (IP addresses).
3. Fragment header -- 包括 fragment 及 reassembly 資訊, 內容包括 Fragment Offset (13 bits), M Flag (1 bit, more/last fragment), Identification (32bits).
4. Authentication header -- 提供 packet integrity (完整性) 及 authentication (認證) 之功能.
5. Encapsulating security payload header -- 提供 privacy (隱密) 之功能.
6. Destination options header -- 包括一些需要 destination node 來處理之 optional 資訊, 其 format 與 hop-by-hop options header 完全相同.

33. The Chain of Pointers Formed by the Next Header field
IPv6 Header
Next Header = 6 (TCP)
TCP Segment (header + data)
IPv6 Header
Next Header = 43 (Routing)
Routing Header
Next Header = 6 (TCP)
TCP Segment (header + data)
IPv6 Header
Next Header = 43 (Routing)
Routing Header
Next Header = 51 (AH)
Authentication Header
Next Header = 6 (TCP)
TCP Segment (header + data)

34. IPv6 Extension Headers IPv6 packet with all extension headers Octets:40
IPv6 specification recommended order:
IPv6 header
Hop-by-hop options header
Destination options header(for intermediate dest. When the routing header is present)
Routing header
Fragment header
Authentication header
Encapsulation security payload header
Destination options header
IPv6 header
Hop-by-hop options header
Variable
Variable
Routing header 8
Fragment header
Variable
Authentication header
Variable
Encap security payload header
Variable
Destination options header
這是 IPv6 packet 包括所有種類 header 之一例, 其中 IPv6 header 和每一 extension header 皆具一 next header field.
當有多個 extension header 出現時, IPv6 spec. 建議其排列次序如右.
20 (optional variable part)
TCP header
Application data
Variable
= Next header field
IPv6 packet with all extension headers

35. Structure of the Routing Header
The same as Record route, strict source, and loose source routing option in IPv4
Next Header
Header Extension Length
Routing Type
Segments Left
Routing type-specific data
. . .
Routing header: specify a source route which is a list of intermediate dest. For the packet to travel to on its path to the final dest.
HEL: 8-byte unit, not include self-8-byte.

36. Structure of the Routing Type 0 Header
Next Header
Header Extension Length
Routing Type
Segments Left
Reserved
Address 1
Address N
. . .
= 0 (loose source routing)
First IP address (filled when started)
Second IP address (filled when started)
Last IP address (filled when started)
Code: 131
Length
(Total length)
Pointer

37. Example Monitor Capture Ipv6: Routing ; Proto =ICMPv6: Len =40
Version =6, Traffic class =0, Flow Label=0, Payload Length=64, Next Header =43,…., Source address: fec0::2:2b0:d0ff:fee9:4143. Destination address: Fec2::2:260:97ff:fe02:6e8f
IPv6: Routing Header
IPv6:Next Header =58 (ICMPv6)
IPv6: Length =2,
IPv6: Type =0
IPv6: Segments Left =1
IPv6 : Reserved
IPv6: Route
IPv6: address = fec0::1:260:8ff:fe52:f9d8
IPv6: Payload: number of remaining =40

38. When the IPv6 packet reaches an intermediate destination, the routing header is processed and:
The current destination address and the address in the (N-Segments Left +1) position in the list of addresses are swapped
The Segments Left field is decremented
The packet is forwarded

39. Quiz(4_1)-loose source routing Example
G4_1: Fill out the loose source with three intermediate destination address: 2001::C001, 2001::C010, 2001::C122
Next Header
Header Extension Length
Routing Type
Segments Left
Reserved
Address 1
Address N
. . .
= 0 (loose source routing)

40. Structure of the Fragment Header (8 bytes)
Next Header
Reserved
Fragment Offset
More Fragments Flag
Identification
Used for IPv6 fragmentation and reassembly services

41. IPv6 Fragmentation Process
Original IPv6 Packet
Unfragmentable part
Fragmentable part
Unfragmentable part
Fragment header
First fragment
Unfragmentable part
Fragment header
Second fragment
Unfragmentable part
Fragment header
Third fragment

42. IPv6 Reassembly Process
Unfragmentable part
Fragment header
Fragmentable part
Unfragmentable part
Fragment header
Fragmentable part
Unfragmentable part
Fragment header
Fragmentable part
Unfragmentable part
Fragmentable part
Original IPv6 Packet

43. Quiz(4_2)-Example of fragment header
Q4-2: For a TCP segment of 4000 bytes, find the fragment header of IPv6 with MTU=1420 bytes.
How many IP datagram are needed?
What kind of IPv6 extension header are needed?
Marked the fields value for those IP datagram related to fragmentation ?
IPv6 Header
Extension
Header
Transport-level PDU

44. Structure of the Hop-by-Hop Options Header
Next Header
Header Extension Length
Options
. . .
Header Extension Length describes the number of 8-byte blocks, not including the first 8 bytes. E.g., for an 8-byte Hop-by-Hop, the value is 0, padding options are used.

45. Structure of an Option Option Type Option Length Option data . . .
An option is a set of fields that either describes a specific characteristic of the packet delivery or provides padding. Options are sent in Hop-by-Hop and Destination Options headers. Each option is encoded in the type-length-value (TLV) format.
Option type Field: option type field both identifies the option and determines the way it is handled.
Two high-order bits indicate how the option is handled by the node, 00 skip the option, 01 silently
Discard the packet, 10 discard the packet and send an ICMPv6 .., 11 discard the packet
and send an ICMPv6 .for not a multicast address. Third high-order bit indicates the option data
can (1) or can not be changed (0) in the path to the destination.

46. Structure of the Pad1 Option
Option Type
= 0
Option type Field:
[Two high-order bits indicate how the option is handled by the node, 00 skip the option, 01 silently Discard the packet, 10 discard the packet and send an ICMPv6 .., 11 discard the packet and send an ICMPv6 .for not a multicast address. Third high-order bit indicates the option data can (1) or can not be changed (0) in the path to the destination.]
Option type of 0: mean skipped if not recognized, not be changed,

47. Structure of the PadN Option
Option Type
Option Length
Option data
= 1
. . .
Option type Field:
[Two high-order bits indicate how the option is handled by the node, 00 skip the option, 01 silently Discard the packet, 10 discard the packet and send an ICMPv6 .., 11 discard the packet and send an ICMPv6 .for not a multicast address. Third high-order bit indicates the option data can (1) or can not be changed (0) in the path to the destination.]
Option type of 1: mean skipped if not recognized, not be changed,

48. Structure of the Jumbo Payload Option
Option Type
Option Length
Jumbo Payload Length
= 194
= 4
Option type Field:
The size in the IPv6 header is invalid, instead the jumbo payload length is used.
Option type of 194 ( ): indicates an ICMPv6 parameter problem if the option is not recognized and the destination address is not a multicast address.

49. Header Extension Length Options
Quiz (5_1)
Quiz (5_1): fill the hop-by-hop extension header with Jumbo Payload Option (value of 224 bytes). Fill out all the fields and draw block diagram i.e., structure between IPv6 header, extension header, and the Data.
IPv6 Header
Hop by hop
Header
Transport-level PDU
Next Header
Header Extension Length
Options
= 194
= 4
. . .

50. Structure of the Router Alert Option
Option Type
Option Length
Router Alert Value
= 5
= 2
= 0
This option Indicates to a router that the contents of the packet require additional processing
. Router Alert Option is used for Multicast Listener Discovery (MLD) and the Resource
ReSerVation Protocol (RSVP).

51. Monitor Capture (5_2) Ipv6: Version =6, Traffic class =0, Flow Label=0, Payload Length=32, Next Header =0,…. IPv6: Hop-by-Hop Options Header IPv6:Next Header =58 (ICMPv6) IPv6: Length =0, IPv6:Router Alert Option IPv6: Type =5 IPv6: Length =2 IPv6 Router Alert Value=0 IPv6: padding (2 bytes) IPv6: Type=1 (PadN) IPv6: length =0 IPv6: Palyload: number of remaining =24

52. Quiz (5_2)
Quiz (5_2): fill the values in the network capture in 5_2 into the relative fields in the hop-by-hop option. and draw the values and relation within the IPv6 header, extension header, and the Data.

53. Structure of the Destination Options Header
Next Header
Header Extension Length
Options
. . .
Dest. Options Header specify delivery parameters for either intermediate dest. Or The final dest.
If a routing header is present, it specifies delivery or processing options at each
Intermediate destination.
If no routing header is present, it specifies delivery or processing options at the final destination.
Dest. Options Header used to supports Mobility in IPV6

54. Structure of the Binding Update Option
Option Type
Option Length
Flags
Reserved
Prefix Length
Sequence Number
Lifetime
Sub-Options
= 198
Used by the mobile IPv6 node to update
another node with its new care-of-address
. . .

55. Structure of the Binding Acknowledgement Option
Option Type
Option Length
Status
Sequence Number
Lifetime
Refresh
Sub-Options
= 7
. . .
Used of acknowledge the receipt of
a binding update

56. Structure of the Binding Request Option
Option Type
Option Length
Sub-Options
= 8
. . .
Used to request the binding from a mobile node.

57. Structure of the Home Address Option
Option Type
Option Length
Home Address
Sub-Options
= 201
. . .
Used to indicate the home address of the mobile node.

58. Structure of the Authentication Header
Next Header
Payload Length
Reserved
Security Parameters Index
Sequence Number
Authentication Data
. . .

59. Structure of the ESP Header and Trailer
Security Parameters Index
Sequence Number
Payload Data
Padding
Padding Length
Next Header
Authentication Data
. . .
. . .
. . .

60. IPv6 MTU Link layer must support a 1280-byte MTU
Otherwise, link layer must use a transparent fragmentation and reassembly scheme
For configurable MTU link layers, MTU size of at least 1500 bytes
Example: Maximum Receive Unit (MRU) of a Point- to-Point Protocol (PPP) link
Path MTU Discovery process uses the ICMPv6 Packet Too Big message

61. Structure of the IPv6 Pseudo-Header
Source Address
Destination Address
Upper Layer Packet Length
Zero
Next Header
= 0

62. Internet 封裝 網際層訊框包裝(Ethernet II) Internet 封裝：網際層封包與 Ethernet 訊框包裝
Type 0800 ：IP v4 封包
Type 86DD: IP v6封包
Type 0806：ARP 封包
Type 0835：RARP 封包

63. Internet 封裝 網際層訊框包裝( IP in in 802.2+802.3 LLC/SNAP)
區域網路封裝：網際層封包與 802.2/802.3 訊框包裝

64. Ethernet II (DIX)Frame
Preamble
SFD
Destination
address
Source
Type
Data
CRC
Preamble: 56 bits of alternating 0s and 1s that alert the receiving system to the coming frame.
SFD: one-byte field( ) is used as a flag.
Destination address:
Source address:
Data: 46 bytes to 1500 bytes
CRC: CRC-32