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Understanding IPv6 Slide: 1

Lesson 4

The IPV4 AND IPv6Header


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Internet layer

Internet layer is responsible for source todestination delivery of a packet across differentnetworks.

Internet layer is not reliable transmission Examples of Network layer Routed protocols

are:

IP

IPX (internetwork packet exchange)

AppleTalk


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Internet layer


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IPv4 Header

Octet +0 Octet +1 Octet +2 Octet +3

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

VER(4) HLEN TOS(QOS) TOTAL LENGTH(16)

IDENTIFICATION(Sequential no.) D

F

M

FFRAGMENT OFFSET

TIME TOLIVE(8) PROTOCOL HEADER CHECKSUM

SOURCE ADDRESS OF HOST(32)

DESTINATION ADDRESS OF HOST(32)

OPTIONS and PADDING


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DSCP (Differentiated service code point)

Total 8 bits are available

First 6 bits are used for DSCP

ds5,ds4,ds3,ds2,ds1,ds0 ds5,ds4,ds3 are used for classes, Total

four classes are available

In each class there are 3 drop levels Low ,medium, high


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IPv4 packet processing

1. Verify the header checksum2. Verify the version field

3. Decrement the TTL value by 1

4. Check the DA and check the localrouting table

5. If no entry in the routing table sendICMP message

6. Recalculate the header checksumand place its new value in theheader checksum

7. Forward the packet on interface


7/15Understanding IPv6 Slide: 7

IPV6 Header

NextHeader(8)

Hop Limit(8)

Flow Label(20)Traffic

Class(8)

Destination Address(128)

Source Address(128)

Payload Length(16)

Version(4)



IPv6 Header Format

IPv6

20 Bytes + Options

Fragment

OffsetFlags

Total LengthType ofService

IHL

PaddingOptions

Destination Address

Source Address

Header ChecksumProtocolTime to Live

Identification

Version

IPv4 Header

NextHeader

Hop Limit

Flow LabelTrafficClass

Destination Address

Source Address

Payload Length

Version

IPv6 Header



Flow Label

This field indicates this packet belongsto a specific sequence of packetsbetween source to destination , which

requires special handling byintermediate routers.

Ex: voice and video

Note; flow label 0 means no flow label.



IPv6 packet processing

1. Verify the version field2. Decrement the hop limit value by 1

3. Check the DA and check the local

routing table4. If no entry in the routing table send

ICMP message

5. Forward the packet on interface.



Comparing the IPv4 and IPv6 Headers

IPv4 Header Field Change in IPv6

Version New value of 6Internet Header Length Removed (Header length is fixed)

Type of Service Traffic Class field

Total Length Payload Length field

Identification Removed to Fragment headerFragmentation Flags Removed to Fragment header

Fragment Offset Removed to Fragment header

Time to Live Hop Limit field

Protocol Next Header field

Header Checksum Removed

Source Address Same, new 128-bit length

Destination Address Same, new 128-bit length

Options Removed (extension headers)


12/15Understanding IPv6Slide: 12

IPv6 HeaderNext Header = 6(TCP)

TCP Segment

IPv6 HeaderNext Header = 43(Routing)

TCP SegmentRouting HeaderNext Header = 6(TCP)

Authentication Header

Next Header = 6(TCP)

IPv6 HeaderNext Header = 43(Routing)

Routing HeaderNext Header = 51(AH)

TCP Segment

The Chain of Pointers Formed by the Next Header field


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Extension Headers Order

1. Hop-by-Hop Options header2. Destination Options header (for

intermediate destinations when the Routingheader is present)

3. Routing header

4. Fragment header

5. Authentication header

6. Encapsulating Security Payload header

7. Destination Options header (for the finaldestination)



Values of the Next Header Field

Value Header

0 Hop-by-Hop Options Header6 TCP

17 UDP

41 Encapsulated IPv6 Header

43 Routing Header

44 Fragment Header

50 Encapsulating Security Payload

51 Authentication Header58 ICMPv6

59 No next header

60 Destination Options Header



Thank you

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