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IP version 6 an Introduction |
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Written by hakimkt
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Wednesday, 26 January 2005 |
Due to the recent explosion in growth the Internet is running out of IP address
space. Solutions to this problem have already been developed, such as Network
Address Translation (NAT.) The problem with solutions such as NAT is that they
do not scale very well. On the small scale they work well and have few problems
if used with well known layer 4 services. But relying on port/address
translation on a large scale is not a good idea. Therefore, your friends at
places such as the IETF and Networking companies have come up with IPv6
Basic Design Concepts
IPv6 is similar to IPv4 in only basic
coneptual design. The idea of splitting an address up into network and host
portions is maintained. A masking is configured on the host so that it can
determine if the layer 2 frame is locally destined, or if it should be sent to a
gateway for processing.
As in IPv4, devices may share a single address,
as long as they masquerade as the same device. This is useful for such
techniques as server load balancing.
IPv6 addresses will be 128 bits in
length, as opposed to 32 bits for IPv4 addresses. The new addresses will be
expressed in hexadecimal format, as opposed to decimal, which IPv4 uses.
Therefore, an IPv6 address will have the
format:
FEDC:BA98:7B54:3210:F7DC:BA78:7654:A456
As you can see,
the address notation is split up into 8 16 bit sections. Note that if there are
leading zeros in any 16 bit section of the address, they may be omitted since
they are not significant digits. Trailing zeros MUST be noted,
however.
Legacy IPv4 addresses may be embedded into IPv6 addresses to
allow for compatibility while migration is taking place. In these instances the
last 32 bits of the IPv6 address will contain the embedded IPv4
address.
In addition to the basic addressing scheme, a new feature called
a flowlabel will be added to the IPv6 header. This is a unique 24 bit identifier
that represents a particular long lasting session between two hosts. This allows
a router to more quickly identify what the proper path to a given destination
is. Flowlabeling is useful for real-time technologies such as video and
audio.
Security will also be available in IPv6. Building encryption into
the 3rd layer makes it available to all services. Currently, encryption is
implemented at the session layer or higher. Building it into the third layer
allows any application using IP to take advantage of a secure
connection.
Address Configuration
Currently there are two
methods defined for IP address configuration in version 6. They
are:
Stateless configuration - IP address is configured at startup time
automatically without any user/server intervention.
Stateful
Configuration - IP address is manually configured using DHCP or other
means.
Stateless Configuration
IPv6 has a feature built in to allow a
network interface to autoconfigure itself. This method is very similar to way in
which an Appletalk node configures an address when it comes up. The interface
must be multicast enabled however. When the interface comes up, it assigns
itself a tentative host address generated from the link-local prefix and the
interface's token. The interface must then determine if the address is already
in use somewhere on the network segment. It will then send out a Neighbor
Solicitation destined for the tenative host address that it is using. If the
address is already in use, the host using that address will respond with a
Neighbor Advertisement. If this is the case, then the host with the tentative
address will drop that address and must be manually configured.
Provided
that the host is able to configure its link local address, it will have IP
connectivity with other hosts on that network segment. The host will then listen
for router advertisements that contain further information about configuring the
network section of the host's address. Certian fields in the routing
advertisements will contain host stateless configuration information. The host
must use this information to fully configure a global address. Routing
information can also be obtained my soliciting it using "All Routers" multicast
address.
Stateful Configuration
Stateful address configuration is more
straightforward than stateless. In this case an administrator assigns the needed
information to each host. This can be done manually or through DHCP. Stateful
configuration can also be used in conjunction with stateless configuration. This
can allow administrators to manually configure some information and let the rest
be autoconfigured to save time.
Anycasting
IPv6 will have
unicast and multicast capabilities. This is nothing new since both were
incorporated into IPv4. A new feature on IPv6 is anycasting. Anycasting will
allow a packet to be sent to any one of a group of nodes. When a unicast address
is assigned to a number of network nodes is becomes an anycast address. Of
course, these nodes must realize this and be configured to handle anycasting.
The point if anycasting is then when a packet is destined to an anycast address,
it will be routed to the closest node having that anycast address. This of
course saves CPU time and bandwidth in the long run.
A possible use of
anycast addresses is to identify a set of routers belonging to one ISP. Other
possible uses are to identify the set of routers attached to a particular
network segment, or each router providing entry into a particular domain or
autonomous system. This will augment distance vector routing protocols in
choosing the shortest path to a
destination.
Summary
Internet Protocol version 6 should
provide ample addressing space for a long time to come. It also has many new
features built in that IPv4 does not have. Features such as built in security
will allow any type of IP service to utilize encryption without extra software.
Host to host authentication will enable identity verification. The stateless
address autoconfiguration feature will decrease the work load on
administrators.
Author :- Hakimkt
Kuwait
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