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For more information please check out my Cisco Press book and video series:
IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6• By Rick Graziani• ISBN-10: 1-58714-313-5
IPv6 Fundamentals LiveLessons: A Straightforward Approach to Understanding IPv6• By Rick Graziani• ISBN-10: 1-58720-457-6
2.1: Comparing the IPv4 and IPv6 Headers
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Let’s Begin with the IPv6 Header
• Understanding IPv6 begins with the IPv6 header.
• IPv6 takes advantage of 64-bit CPUs.
• Several differences between IPv4 and IPv6 headers.
IPv4
IPv6
64-bit memory word• Simpler IPv6 header.
• Fixed 40 byte IPv6 header.
• Lets look at the differences…
Similar fields
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IPv6 Version
• IPv4 Version contains 4.• IPv6 Version contains 6.• Version 5?• Internet Stream Protocol (ST2)
IPv4
IPv6
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IPv4 Internet Header Length• IPv4 Internet Header Length (IHL)
• Length of IPv4 header in 32-bit words including any Options or Padding.
• IPv6• IHL for IPv6 is not needed.• IPv6 header is fixed at 40 bytes.
IPv4
IPv6
8 bytes
8 bytes
8 bytes
8 bytes
8 bytes
40 bytes =
1
2
3
4
5
?
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IPv6 Traffic Class• IPv4 Type of Service• IPv6 Traffic Class
• Not mandated by any IPv6 RFCs.• Same functionality as IPv4.• Uses same Differentiated Services
technique (RFC 2474) as IPv4.
IPv4
IPv6
7 6 5 4 3 2 1 0
IP Precedence Unsused
DiffServ Code Point (DSCP) IP ECN
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IPv6 Flow Label
• New field in IPv6 – not part of IPv4.• Flow label is used to identify the packets in a common stream or flow. • Traffic from source to destination share a common flow label.• RFC 6437 IPv6 Flow Label Specification
IPv4
IPv6
11001011000101100
10110010111000111
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IPv6 Payload Length• IPv4 Total Length – Number of bytes of
the IPv4 header (options) + data.• IPv6 Payload Length – Number of bytes
of the payload.• Does not include the main IPv6
header.• Includes extension headers + data
IPv4
IPv6
IPv6 Header DataIPv6 Extension Header (Optional)
IPv4 Header Data (Payload)
Payload
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IPv4 Fragmentation• IPv4 fields used for fragmentation and
reassembly.• Intermediate devices such as IPv6
routers do not perform fragmentation.• Any fragmentation needed will be
handled by the source using an extension header.
IPv4
IPv6
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IPv6 Next Header
• IPv4 Protocol• IPv6 Next Header • For both protocols, the field indicates
the type of header following the IP header.
IPv4
IPv6
• Common values:• 6 = TCP• 17 = UDP• 58 = ICMPv6• 88 = EIGRP• 89 = OSPF
IPv6 Header
NextHeader
Data(Protocol: TCP, UDP, ICMPv6, etc.)
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IPv6 Hop Limit
• IPv4 TTL (Time to Live)• IPv6 Hop Limit• Renamed to more accurately reflect
process.• Set by source, every router in path
decrements hop limit by 1.
IPv4
IPv6• When 0,
drop packet.
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IPv6 Source and Destination Addresses
• IPv6 Source and Destination addresses have the same basic functionality as IPv4.
• IPv4 – 32-bit addresses.• IPv6 – 128-bit addresses.• Some significant changes in IPv6.
IPv4
IPv6
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IPv4 Header Checksum• IPv4 Header Checksum• Not used in IPv6.• Upper-layer protocols generally have
a checksum (UDP and TCP).• So, in IPv4 the UDP checksum is
optional.
IPv4
IPv6• Because it’s
not in IPv6, the UDP checksum is now mandatory.
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IPv4 Options and Padding• IPv4 Options and Padding • Not used in IPv6.• Variable length, optional.• IPv4 Options are handled using
extension headers in IPv6.
IPv4
IPv6
• Padding makes sure IPv4 options fall on a 32-bit boundary.
• IPv6 header is fixed at 40 bytes.
40 bytes =
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IPv6 Extension Header
• Next Header identifies:• The protocol carried in the
data portion of the packet.
IPv6 Main Header
NextHeader
Extension Header
NextHeader
Data(Protocol: TCP, UDP, ICMPv6, etc.)
• Extension headers are optional and follow the main IPv6 header.• Provide flexibility and features to the main IPv6 header for future
enhancements without having to redesign the entire protocol. • Allows the main IPv6 header to have a fixed size for more
efficient processing.
• The presence of an extension header.
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IPv6 Extension HeaderNext Header Value (Decimal)
Extension Header Name
Extension Header Description
0 Hop-by-Hop Options Used to carry optional information, which must be examined by every router along the path of the packet.
43 Routing Allows the source of the packet to specify the path to the destination.
44 Fragment Used to fragment IPv6 packets.
50 Encapsulating Security Payload (ESP)
Used to provide authentication, integrity, and encryption.
51 Authentication Header (AH)
Used to provide authentication and integrity.
60 Destination Options Used to carry optional information that only needs to be examined by a packet’s destination node(s).
IPv6 Main Header
Next Header
0
Hop-by-Hop Extension
Header
Next Header
51
TCP Header
AH Extension Header
Next Header
6Data
2.2: A Brief Look at IPv6 Address Types
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IPv6 Address Types
IPv6 Addresses
FF00::/8 FF02::1:FF00:0000/104
::/128::1/1282000::/3 FE80::/10 FC00::/7 ::/80
Unicast Multicast Anycast
Assigned Solicited Node
Global Unicast
Link-Local Loopback UnspecifiedUnique Local
Embedded IPv4
More details in Lessons 3, 4, 5 & 6
2.3: A Brief Look at ICMPv6 Neighbor Discovery
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ICMPv6Internet Control Message Protocol for IPv6
• ICMPv6 is defined in RFC 4443.• Similar to ICMPv4, describes two types of
messages:• Informational• Error
• ICMPv6 Neighbor Discovery is described in RFC 4861.
• Much more robust than ICMP for IPv4.• Contains new functionality and improvements. • More than just “messaging” but “how IPv6
conducts business”.IPv6 Main
Header
Next Header
58
ICMPv6 Header
DataAll ICMPv6 messages
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ICMPv6 Neighbor Discover Protocol
• Router Solicitation Message• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
• Redirect Message Similar to ICMPv4 redirect message Router-to-Device messaging
Router-Device Messaging
Device-Device Messaging
ICMPv6 Neighbor Discovery defines 5 different packet types:
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Router Solicitation & Router Advertisement Messages
• Router Solicitation Message• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
• Redirect Message Similar to ICMPv4 redirect message Router-to-Device messaging
Router-Device Messaging
Device-Device Messaging
ICMPv6 Neighbor Discovery defines 5 different packet types:
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Dynamic Address Allocation in IPv4DHCPv4 Server
1
2
I need IPv4 addressing information.
Here is everything you need.
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Dynamic Address Allocation in IPv6
DHCPv6 Server
ICMPv6 Router Advertisement
ICMPv6 Router Solicitation
To all IPv6 routers: I need IPv6 address
information.
To all IPv6 devices:Let me tell you how
to do this … 1. SLAAC
2. SLAAC with Stateless DHCPv6
3. Stateful DHCPv6
SLAAC (Stateless Address Autoconfiguration)
I might not be needed.
Router SolicitationsRouter Advertisements
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Neighbor Solicitation & Neighbor Advertisement Messages
• Router Solicitation Message• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
• Redirect Message Similar to ICMPv4 redirect message Router-to-Device messaging
Router-Device Messaging
Device-Device Messaging
ICMPv6 Neighbor Discovery defines 5 different packet types:
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Ethernet ARP Request/Reply
ICMPv6: Neighbor Solicitation/Advertisement
IPv4: ARP over Ethernet
PCAPCBARP Request
Neighbor Advertisement
1
2Neighbor
Solicitation
1
ARP Reply
2
Know IPv4, what
is the MAC?
My IPv4! Here is the
MAC?
Know IPv6, what
is the MAC?
My IPv6! Here is the
MAC?
ARP Request: Broadcast
NS: Multicast NS: Solicited Node Multicast
Ethernet IPv6 Header
IPv6: ICMPv6 over IPv6 over Ethernet
Address Resolution: IPv4 and IPv6
ARP Cache
Neighbor Cache
Neighbor SolicitationsNeighbor Advertisements
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Redirect Message
• Router Solicitation Message• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
• Redirect Message Similar to ICMPv4 redirect message Router-to-Device messaging
Router-Device Messaging
Device-Device Messaging
ICMPv6 Neighbor Discovery defines 5 different packet types:
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ICMPv6 Redirect
• Similar functionality as ICMPv4.• Like IPv4, a router informs an originating host of the IP address of a router that
is on the local link and is closer to the destination. • Unlike IPv4, a router informs an originating host that the destination host (on a
different prefix/network) is on the same link as itself.
Network X
PCA PCB
R1 R2
Destination:Network X Host
Destination:PCB
IPv6 Network A IPv6
Network B
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ICMPv6 Neighbor Discover Protocol
• Router Solicitation Message• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
• Redirect Message Similar to ICMPv4 redirect message Router-to-Device messaging
Router-Device Messaging
Device-Device Messaging
ICMPv6 Neighbor Discovery defines 5 different packet types:
More details in Lessons 7, 8 & 10
©
For more information please check out my Cisco Press book and video series:
IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6• By Rick Graziani• ISBN-10: 1-58714-313-5
IPv6 Fundamentals LiveLessons: A Straightforward Approach to Understanding IPv6• By Rick Graziani• ISBN-10: 1-58720-457-6
