2: Comparing IPv4 and IPv6
Rick Graziani
Cabrillo College
Rick.Graziani@cabrillo.edu
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
Let’s Begin with the IPv6 Header
Similar fields
• Understanding IPv6 begins with the IPv4
IPv6 header.
• IPv6 takes advantage of 64-bit
CPUs.
• Several differences between IPv4
64-bit memory word
IPv6IPv6
headers.
• and
Simpler
header.
IPv6
• Fixed 40 byte
IPv6 header.
• Lets look at
the
differences…
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IPv6 Version
•
•
•
•
IPv4 Version contains 4.
IPv6 Version contains 6.
Version 5?
Internet Stream Protocol (ST2)
IPv4
IPv6
©
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
1
2
3
4
5
?
IPv6
8 bytes
8 bytes
40 bytes =
8 bytes
8 bytes
8 bytes
©
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
IP Precedence
4
3
2
1
0
Unsused
DiffServ Code Point (DSCP)
IP ECN
©
IPv6 Flow Label
•
•
•
•
IPv4
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
11001011000101100
10110010111000111
IPv6
©
IPv6 Payload Length
IPv4 Header
• 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
Data (Payload)
IPv4
IPv6
Payload
IPv6 Header
IPv6 Extension
Header (Optional)
Data
©
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
©
IPv6 Next Header
• IPv4 Protocol
IPv4
• IPv6 Next Header
• For both protocols, the field indicates
the type of header following the IP
header.
• Common values:
• 6 = TCP
IPv6
• 17 = UDP
• 58 = ICMPv6
IPv6
Next
• 88 = EIGRP
Header
Header
• 89 = OSPF
Data
(Protocol: TCP, UDP, ICMPv6, etc.)
©
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.
• When 0,
IPv6
drop packet.
IPv4
©
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
©
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.
• Because it’s
not in IPv6, IPv6
the UDP
checksum is
now
mandatory.
IPv4
©
IPv4 Options and Padding
•
•
•
•
IPv4 Options and Padding
Not used in IPv6.
Variable length, optional.
IPv4 Options are handled using
extension headers in IPv6.
• Padding makes
sure IPv4 options
fall on a 32-bit
IPv6
boundary.
• IPv6 header is
fixed at 40 bytes.
IPv4
40 bytes =
©
IPv6 Extension Header
• Next Header identifies:
• The protocol carried in the
data portion of the packet.
• The presence of an extension header.
• 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.
IPv6 Main
Header
Next
Header
Extension
Header
Next
Header
Data
(Protocol: TCP, UDP, ICMPv6, etc.)
©
IPv6 Extension Header
Next 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
AH Extension
Header
Next
Header
6
TCP
Header
Data
©
2.2: A Brief Look at IPv6 Address Types
More details in
Lessons 3, 4, 5 & 6
IPv6 Address Types
IPv6 Addresses
Unicast
Multicast
Assigned
FF00::/8
Anycast
Solicited Node
FF02::1:FF00:0000/104
Global
Unicast
Link-Local
Loopback
Unspecified
Unique
Local
Embedded
IPv4
2000::/3
FE80::/10
::1/128
::/128
FC00::/7
::/80
©
2.3: A Brief Look at ICMPv6
Neighbor Discovery
ICMPv6
Internet 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”.
Next
IPv6 Main
All ICMPv6
messages
Header
Header
58
ICMPv6
Header
Data
©
ICMPv6 Neighbor Discover Protocol
ICMPv6 Neighbor Discovery defines 5 different packet types:
• Router Solicitation Message
• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message
• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
Router-Device
Messaging
Device-Device
Messaging
• Redirect Message
Similar to ICMPv4 redirect message
Router-to-Device messaging
©
Router Solicitation & Router Advertisement Messages
ICMPv6 Neighbor Discovery defines 5 different packet types:
• Router Solicitation Message
• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message
• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
Router-Device
Messaging
Device-Device
Messaging
• Redirect Message
Similar to ICMPv4 redirect message
Router-to-Device messaging
©
Dynamic Address Allocation in IPv4
DHCPv4 Server
1
2
I need IPv4
addressing
information.
Here is everything
you need.
©
Dynamic Address Allocation in IPv6
To all IPv6 routers:
I need IPv6 address
information.
I might not be
needed.
ICMPv6 Router Solicitation
DHCPv6 Server
To all IPv6 devices:
Let me tell you how
to do this …
ICMPv6 Router Advertisement
1. SLAAC
2. SLAAC with
Stateless DHCPv6
SLAAC
(Stateless Address Autoconfiguration)
Router Solicitations
Router Advertisements
3. Stateful DHCPv6
©
Neighbor Solicitation & Neighbor Advertisement Messages
ICMPv6 Neighbor Discovery defines 5 different packet types:
• Router Solicitation Message
• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message
• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
Router-Device
Messaging
Device-Device
Messaging
• Redirect Message
Similar to ICMPv4 redirect message
Router-to-Device messaging
©
Address Resolution: IPv4 and IPv6
ARP Request: Broadcast
IPv4: ARP over Ethernet
Ethernet
ARP Request/Reply
ARP
Cache
My IPv4!
Here is the
MAC?
PCB
2
1
ARP Reply
ARP Request
1
2
My IPv6!
Here is the
MAC?
Neighbor
Solicitation
Neighbor
Advertisement
IPv6: ICMPv6 over IPv6 over Ethernet
NS: Multicast NS: Solicited Node Multicast
Ethernet
IPv6 Header
PCA
Neighbor
Cache
Know
IPv4, what
is the
MAC?
Know
IPv6, what
is the
MAC?
Neighbor Solicitations
Neighbor Advertisements
ICMPv6: Neighbor Solicitation/Advertisement
©
Redirect Message
ICMPv6 Neighbor Discovery defines 5 different packet types:
• Router Solicitation Message
• Router Advertisement Message
Used with dynamic address allocation
• Neighbor Solicitation Message
• Neighbor Advertisement Message
Used with address resolution (IPv4 ARP)
Router-Device
Messaging
Device-Device
Messaging
• Redirect Message
Similar to ICMPv4 redirect message
Router-to-Device messaging
©
ICMPv6 Redirect
Network X
R1
R2
Destination:
Network
PCB
X Host
IPv6
Network A PCA
•
•
•
PCB
IPv6
Network B
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.
©
ICMPv6 Neighbor Discover Protocol
ICMPv6 Neighbor Discovery defines 5 different packet types:
• 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
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
©
2: Comparing IPv4 and IPv6
Rick Graziani
Cabrillo College
Rick.Graziani@cabrillo.edu