Transcript 13.4 IPv6 Extension Headers

13.1 Introduction
• Existing IP (v4) was developed in late 1970’s, when computer memory
was about 32 Kbytes (215), to 512 Mbytes (229) or more today,
processor speed, core network speed also increased by a factor of
about 1000 times. Internet users have increased by many millions.
• The flexibility of IP and other measures such as VLSM/CIDR, DHCP,
NAT, extended the life of IPv4 until today, but it is not going to
accommodate the projected growth.
• Three main factors for the development of a new version of IP :
– The need for more addresses
– The need for guarantee of Quality of Services (QoS)
– The need for secure communication (sender authentication)
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13.2 Basic Features of IPv6
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IPv6 (RFC1883, 2460) is also known as IP – The Next Generation
(IPng)
128 bit address, will not be exhausted in the foreseeable future and
improve addressing structure (RFC1884, 2373).
Flexible and simplified header format. IPv6 uses a set of optional
headers.
Improved options. Enhanced traffic control options.
Support for network resource allocation. The IPv4 TOS field is
replaced with a class field which can support real-time services
Capability for extensions.
13.3 IPv6 Datagram
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Optional
General form:
Base
Header
Extension
Header 1
… Extension
Header n
Data …
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• Base header (40 octets) format:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class |
Flow Label
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length
| Next Header | Hop Limit
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address
(128-bit, 16 Octets)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address
(128-bit)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
• Version: 4-bit field specifies the version (6).
• Traffic Class: 8-bit traffic class field. This is used by a host or router to
distinguish and differentiate priorities of IPv6 packets. Similar to IPv4
DiffServ TOS field.
• Flow Label: 20-bit flow label. This is used by a source to label
sequences of packets that may require special handling by routers, e.g.
a real-time service. This and the field above provides the basis for IPv6
QoS.
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• Payload Length: 16-bit field specifies the number of octets carried in
the datagram excluding this header.
• Next Header: 8-bit field. Each of the base and extension headers
contains such a field, which is used to identify the type of header
immediately following this header. Similar to IPv4 Protocol field.
• Hop Limit: 8-bit field similar to IPv4 TTL field.
• Source/Destination Address are the addresses of sender and the
intended recipient (may not be the ultimate recipient if a routing header
exists).
13.4 IPv6 Extension Headers
• IPv6 packets may carry zero or more extension headers, each is
identified by the Next Header field.
• IPv6 extension headers work like v4 options. They serve the purposes
of fragmentation, source routing and authentication. They are optional
and can be selectively applied. New functions can also be developed.
• There is an order of the extension headers when more than one is used.
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• The extension headers are not processed until the packet reaches the
first intended recipient.
• The parsing of an IPv6 datagram depends on the next header field in
the base and extension header (if any).
• Fragmentation (with an extension header) is restricted to source only,
not an intermediate router like v4. A Path MTU discovery must be
performed by the source to identify the minimum MTU along the route
to destination. The fragmentation and reassembly in IPv6 is therefore
end-to-end. The Fragment Extension Header is used for this purpose.
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• End-to-end fragmentation
is designed to reduce
the load of routers but does
not accommodate route
changes. If route change
happens and the MTU is
smaller than that originally
discovered by the source, the
intermediate router must
perform tunneling.
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• IPv6 uses routing extension header for (loose) source routing.
• IPv6 has two more extension headers to accommodate other IPv4
options. These are Hop-by-Hop Options and Destination Options
extension headers.
13.4 IPv6 Address
• The address space is so large that everyone on earth now can have an
internet as large as the current internet. The address space is about
3.4x1038, can not be exhausted with current and foreseeable
technology. (It takes 20 years to assign at the rate of 1 million per us)
• Colon Hexadecimal Notation for human consumption. Dotted Decimal
will be too long, e.g.
104.230.140.100.255.255.255.255.0.0.17.128.150.10.255.255
is represented as: 68E6:8C64:FFFF:FFFF:0:1180:96A:FFFF
• Colon hex notation allows zeros to be compressed with a pair of
colons, eg
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FF05:0:0:0:0:0:0:B3 can be written as FF05::B3
IPv4 addresses can be mapped to v6. For example: 130.194.226.4 in
IPv6 will be 0:0:0:0:0:0:130.194.226.4, or ::130.194.226.4 Note the
mixture of v4 and v6 expressions.
Three IPv6 address types
– Unicast: for a single connection on a host or router
– Anycast/Cluster: A set of host connections share the same address,
datagram is delivered to the closest member.
– Multicast: A set (group) of hosts at multiple locations. Each
requires a copy of the datagram.
IPv6 does not use the term broadcast, it treats broadcast as a special
case of multicast. It is easy to emulate broadcast with multicast.
Allows multiple, simultaneous addresses per network connection, and
also multiple prefix per network.
Proposed address allocation (over 72% has been reserved for future
use):
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• In RFC2373, IPv6 address format has been updated. A 64-bit MAC address
has been included in the unicast IPv6 address.
• Geographic-based allocation was discontiued.
• Addresses available for local use (private addresses) are divided into linkand site-local addresses. The former for a single physical network while the
latter for an organisational intranet.
• The term provider-based unicast address has been changed to
aggregatable global unicast address, illustrated as follows (P Loshin):
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• FP: Three-bit field to identify where it belongs in the IPv6 address
space.
• TLA ID: The top-level aggregation identifier contains the highest-level
routing information of the address (13-bit).
• RES: Reserved for future use (8-bit).
• NLA ID: The next-level aggregation identifier (24-bit). This can be
used by large organisations or ISPs to plan their address hierarchy.
• SLA ID: The site-level aggregation identifier (16-bit). This is given to
organisations to plan their internal network (subnet) structure.
• Interface ID: This field (64-bit) contains globally unique interface
identifier (MAC address). This is based on the IEEE EUI-64 format.
This field is big enough to allocate a different address for each
interface.
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