IPv6 Tutorial Module 1: IPv6 Protocol Structure Dan Campbell, President Millennia Systems, Inc.

2 Contents IPv4 header review IPv6 header construction –Version –Traffic Class –Flow Label –Payload Length –Next Header –Hop Limit –Addresses Extension headers –Hop-by-Hop –Destination Options –Routing –Fragmentation –Authentication Header –Encapsulating Security Payload –Mobility

3 Review: The IPv4 header consists of 15 fields (including 3 flags and the options and padding) VerIHLToSTotal Length Fragment Offset TTLProtocolHeader ChecksumSource AddressDestination AddressOptions and Padding IPv4 Header Several of the fields initially envisioned for use either went unused, became obsolete in favor of other technologies or OSI layers, or morphed into other uses Version – Indicates IP version 4 IHL = Internet Header Length, which must be specified since the options allow for varying length headers Total Length – indicates the total length of the IP packet, including the header, upper layer protocols and payload Identifier – Unique identifier for the packet, seldom used Flags – Used to indicate fragmentation Fragment Offset – indicates this fragment’s position in the datagram TTL = Time to Live, the packet life remaining in router hops (and initially in seconds) Header Checksum – used in checking to ensure the header was received as it was transferred and without error Addresses – 32-bit designators for the sending (source) host and receiving (destination) host Options – Seldom used options set by sender Fla gs Identifier ToS = Type of Service, which allows for differentiating packets into different classes for specific forwarding treatment. Protocol – The next protocol header above IP, e.g., TCP, UDP, IPSec, etc.

4 Review: The IPv4 header can vary in size VerIHLToSTotal LengthIdentifier Fragment Offset TTLProtocolHeader ChecksumSource AddressDestination AddressOptions and Padding IPv4 Header 20 bytes Header size can vary if options are used The IPv6 header was designed to optimize the protocol and fix the header to a consistent size to expedite packet forwarding Fla gs

5 IHLIdentifierHeader ChecksumOptions and Padding Fla gs Fragment Offset IPv6 set out to retire obsolete IPv4 header fields VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv4 header fields that were obsolete or superfluous to other protocol layers were identified for deletion or modification IHLIdentifier Fragment Offset Header ChecksumOptions and Padding Fla gs

6 IHL IPv6 header is fixed to 40 bytes VerTotal LengthIdentifier Fragment Offset Fla gs TTLProtocolHeader ChecksumSource AddressDestination AddressOptions and Padding IPv4 Header IHL Internet Header Length (IHL) field is no longer needed ToS

7 Identifier The largely unused Identification field was trashed VerToSTotal Length Fragment Offset Fla gs TTLProtocolHeader ChecksumSource AddressDestination AddressOptions and Padding IPv4 Header Identifier

8 Fla gs The 3-bit Flags field is no longer needed VerToSTotal Length Fragment Offset TTLProtocolHeader ChecksumSource AddressDestination AddressOptions and Padding IPv4 Header Flags dealt primarily with Fragmentation, which has been moved to an optional extension header Fla gs

9 Fragment Offset Fragmentation by routers in IPv6 is not permitted VerToSTotal LengthTTLProtocolHeader ChecksumSource AddressDestination AddressOptions and Padding IPv4 Header Fragment Offset Hosts must fragment packets. Fragmentation was moved to an optional extension header

10 Header Checksum Header checksum was deemed redundant VerToSTotal LengthTTLProtocolSource AddressDestination AddressOptions and Padding IPv4 Header Header Checksum Layer 2 and upper layer protocols are performing checksums, so an IP header checksum is unnecessary

11 The Options field was removed VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header Options and Padding Options forms the basis of the Extension Header concept

12 The Version field was maintained VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Of course, the version numbers was changed to “6”

13 ToS field was kept but renamed to Traffic Class VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Traffic Class Traffic Class is functionally identical to DiffServ (DSCP)

14 A new QoS Field called Flow Label was added VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Traffic Class Flow Label Flow label allows for flow identification at layer 3 and within the IP header, instead of a mix of layer 3 and 4 parameters.

15 Total Length field changed to Payload Length VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Traffic Class Payload LengthFlow Label Header length is fixed to 40 bytes, thus only the payload length needs be identified

16 Protocol field was changed to Next Header VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Traffic Class Flow LabelPayload Length Next Header Next Header could indicate the layer 4 protocol (TCP, UDP), ICMP, another layer 3 IP protocol or an IPv6 extension header.

17 TTL field was kept but changed to Hop Limit VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Traffic Class Flow LabelPayload Length Next Header Hop Limit Over time, the “time” to live field came to mean “router hop count”, thus it was changed in IPv6 to “hop limit”

18 Source and Destination addresses are increased from 32 to 128 bits each VerToSTotal LengthTTLProtocolSource AddressDestination Address IPv4 Header IPv6 Header Ver Traffic Class Flow LabelPayload Length Next Header Hop Limit Source Address (128 bits) Destination Address (128 bits)

19 Traffic Class IPv6 basic header length VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Always 40 bytes Extension headers are added after the addresses, indicated by the Next Header value

20 No Next Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Next Header value = 59

21 Hop-by-Hop header Hop-by-Hop Options Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Provides information that must be examined by every node along the packet’s delivery path, unlike other headers, which are only viewed by the receiving node. Next Header value = 0

22 Destination Options header Hop-by-Hop Options HeaderDestination Options Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Carries optional information that needs to be examined by only the packet’s destination node(s) Destination Options header follows Hop-by- Hop header only when the Routing header is present. Next Header value = 60

23 Routing header Hop-by-Hop Options HeaderDestination Options HeaderRouting Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Used by an IPv6 source to list one or more intermediate nodes to be visited on the way to a packet’s destination. Provides a means to do source or policy routing. Next Header value = 43

24 Fragment header Hop-by-Hop Options HeaderDestination Options HeaderRouting HeaderFragment Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Indicates that the datagram was fragmented and what position this fragment is in the overall datagram Next Header value = 44

25 Authentication Header Hop-by-Hop Options HeaderDestination Options HeaderRouting HeaderFragment HeaderAuthentication Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Provides authentication of the packet Same as AH in IPSec for IPv4 Next Header value = 51

26 Encapsulating Security Payload header Hop-by-Hop Options HeaderDestination Options HeaderRouting HeaderFragment HeaderAuthentication HeaderEncapsulating Security Payload Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address ESP provides confidentiality and integrity of the packet through encryption Same as ESP in IPSec for IPv4 Next Header value = 50

27 Mobility header Hop-by-Hop Options HeaderFragment HeaderAuthentication HeaderEncapsulating Security Payload HeaderMobility Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Used by mobile nodes, correspondent nodes and home agents in messaging related to the creation and management of mobile bindings Next Header value = 135

28 Destination Options header Hop-by-Hop Options HeaderFragment HeaderAuthentication HeaderEncapsulating Security Payload HeaderMobility HeaderDestination Options Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Destination Options header moves to the end if the Routing header is not present Destination Options Header Next Header value = 60

29 Next header is TCP TCP Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Next Header value = 6

30 Next header is UDP UDP Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Next Header value = 17

31 Next header is ICMPv6 ICMPv6 Header Traffic Class VerFlow LabelPayload Length Next Header Hop Limit Source AddressDestination Address Next Header value = 58

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