So
we are running out (have ran out?) of IPv4 addresses. They
have been with us since the very beginning, they were there during
the 1980`s when everything was calm, and they stuck by us during the
chaotic growth of the Internet during the 1990`s. There were
some rumors, during the 2000`s, that they were going to run out soon,
but something called Classless Inter-Domain Routing (CIDR) and
Network Address Translation/Port Address Translation (NAT/PAT)
saved our butts... for a while.
These
4 little sets of numbers, called
Octets, separated by dots were very mysterious, we used
to look at them from the corner of our eyes asking our selves; What
are they for?... What do they do?... How do they do it?
We
were intimidated just by looking at them, and they were just 4 little
sets of decimal numbers, numbers that we recognize, that we use every
day in our daily lives.
And
then, we found out that they were hiding something, they were just
expressed in a decimal format (called dotted-decimal),
when in reality they were written in something called Binary, and
that they were not 4 little sets of decimal numbers but 4 octets
with 8bits each for a
total of 32 binary 1s
and 0s!... and that´s
not all, there were 2^32
of them, which is 4,294,967,296. Oh my God! What is
going on?...
But
time went by and we, the “network guys”, in the long run
became accustom to these little guys. We learned that they uniquely
identify a device on the network. That they have a friend, called the
Sub-net Mask that indicates to what network they belong to,
we've even learned to break them in small chunks according to the
size of our network, using sub-netting, so we wouldn't waste
them... we were taking care of them.
Regardless,
no matter what we do to preserve them, we were going to run out soon
enough. Something had to be done... Introducing, Internet
Protocol Version 6...
and get this, it is NOT
a string of 32
but 128
binary 1s
and 0s!
It is NOT
4 little fields separated by dots, it´s 8 16bits
fields called Hextets,
separated by colons ( :
)! It is
NOT
expressed in decimal format but in Hexadecimal
format!.. and there are not 2^32
but 2^128
of them, which is... are you ready?...
340,282,366,920,938,463,463,374,607,431,464,133,816
(for
those of you who are just starting out and don´t know, the number is
340
undecillion... plus
change).
I
mean, I understand that the world cannot continue in its current form
without the Internet, but come on!! What are they trying to do
to us?
Advantages
Over IPv4.
As you know, the
migration over to IPv6 has already started, but you haven't
noticed it maybe, because IPv4 is still around and it will
still be around for a long time. There are many reasons why IPv4 is
still around; NAT/PAT, CIDR and also, it works fine and
we know how it works.
But, we also know that
there are no more IPv4 addresses to give out and this is the
main reason why we have to migrate to IPv6.
But what about the people
that already have IPv4 addresses assigned, I mean they have them for
good right, so what makes them want to migrate to IPv6?
The answer is because not
only there is an almost infinite amount of addresses available in
IPv6 (and we will NEVER ran into the same shortage
problem again... right?), but also because IPv6 has
some pretty good advantages over IPv4.
Let´s
see a few:
- Better End-to-End Connectivity:
- One of the features that allowed IPv4 to exist beyond what was expected, is NAT. However, NAT is not a very good point-to-point communicator. Host A thought it was talking directly with Host B when in fact, it wasn't.
Well, IPv6, because of its vast address space size, no longer needs the use of NAT. It allows for direct end-to-end communication from Host A to Host B... no middle man.
- Better Auto-configuration.
- For a host to get the info needed to join a network, IPv4 uses DHCP (Dynamic Host Config Protocol) which is a stateful method, meaning the host receives all the info from a server.
IPv6 has both a stateful (DHCPv6) and stateless methods where hosts are able to auto-configure themselves with the info needed to join the network (no server).
- More Efficient Header:
- There is a significant improvement on processing time because many rarely used fields from the IPv4 header have been either removed, or moved to an optional header called “extension Header”. This extension header is only implemented by intermediate routers if a packet needs special handling.One of the fields that have been removed is the Checksum field. Routers no longer have to compute a checksum every time they receive a packet. With IPv6, checksum and error control is handled by upper-layer protocols.
- Better Security.
- IPv6 has support for IPSec which provides for Data Confidentiality, Integrity and Authentication at layer 3. With IPv4, end devices provided this level of security.
- Better QoS Support.
- This is accomplished through the use of a field in the header called Flow Label. Routers are able to use this field to mark specific flows of packets such as packets that require QoS treatment.
- Built-in Mobility Support:
- IPv6 hosts have the ability to move around the network and maintain its IP address.
- Transition Tools.
- Tunneling
- NAT64
- 6to4
- SIIT
- DNS64
- etc.
An
IPv6
address consists of 32 hexadecimal
numbers, separated by colons
( : ) into
8 hextets
of 4 hex
numbers each. Each hex number represents 4
bits, that is 16bits
per hextet
for a total of 128bits
(4bits
x 4 hex
digits per hextet x 8
hextets= 128bits).
Here
is an example:
2001:0AC8:1234:0000:0000:0000:0000:0678
Let´s break it down into
binary. We are not going to do the whole number, but lets do the 1st
and 2nd hextets at least:
Remember, to figure out
binary, you need to use the place values, and they are; 8
4 2 1 for a 4 bit value like in this case (each hex digit).
So, for example, hex
number A on the second hextet (which is 10 in decimal), there
is a 0 on place value 1, a 1 on place value 2,
a 0 on place value 4 and another 1 on place
value 8. Now just add the values that have 1s, 2+8=10.
IPv6 Short Notation.
As you can see, an IPv6
address is very long, right? Let´s imagine this scenario: You arrive
at work and there´s an email from your boss, asking you very nice
and politely... sort of, that all 100 PCs for the upcoming
event are in Show Room C, and that you need to configure these
PCs, for some odd reason, with IPv6 addresses... manually.
Well... your next step
should be texting (texting, is that an obsolete word now?) your wife
to let her know that you are not going to get home on time this
evening, am I correct?
Fortunately, some genius
people already thought about (or went through!) this scenario, and
they came up with a way to be able to write an IPv6 address in
a much shorter way. Let´s see it.
First, you need to
understand the rules, they are very simple:
- Leading zeroes on each hextet can be omitted. Leading zeroes only. So:
- 2001:0AC8:1234:0000:0000:0000:0000:0678 can be written as:
- 2001:AC8:1234:0:0:0:0:678
- Contiguous hextets of zeroes, can be represented with the use of double colons (: :).
This can only be implemented one time per address. So: - 2001:0AC8:1234:0000:0000:0000:0000:0678 can be written as:
- 2001:0AC8:1234::0678
- And finaly, we can combine rules 1 and 2. So:
- 2001:0AC8:1234:0000:0000:0000:0000:0678 can be written as:
- 2001:AC8:1234::678
Also, we can still use
“Slash Notation” or “CIDR Notation” as we did
with IPv4. For example, if the first 64 most
signifficant bits indicate the network bits or Network ID, we
can notate it with a slah ( / ) and the
number of bits i the network ID, like this /64.
So, we can write the
whole address as follows:
2001:AC8:1234::678/64
On this particular
example, we ended up with a shorter IPV6 address, only 14 hex
digits as opossed to 32 in a full address. However, depending on the
original, full address, we can end up with an address that is only 10
characters long, and that is very good if you need to enter these
addresses manually. Lets see:
Original:
2001:0000:0000:0000:0000:0000:0000:0001/64
Let`s
remove the leading zeroes: 2001:0:0:0:0:0:0:1/64
Or,
we can us the double colon: 2001::1/64
IPv6 Address Types.
In IPv4 we have 3
types of addresses; Unicast, Multicast and Broadcast.
For IPv6, even though there is no more Broadcast address, there
are several types of addresses and they are assified within 3 main
types.
They are:
- Unicast
- One-to-one communication. Unique address assigned to an interface, a packet sent to a Unicast address will be received by one single interface. There are several types of Unicast addresses:
- Global Unicast.
- Link Local.
- Unique Local. (in place of Site-Local which was deprecated in 2004)
- Unspecified.
- Loopback.
Multicast
- One-to-many communication. A Multicast address identifies a group of interfaces. A packets sent to a Multicast address are received by a group of interfaces that may be in different hosts.
Anycast
- Special one-to-one communication. An Anycast address represents a group of interfaces, but the packet sent to this address will be deliver only to the interface which is closest, in terms of the routing protocol cost value.Also, since Anycast addresses are allocated from the Unicast address space, they are syntactically indistinguishable from each other. So, an Anycast address is a Unicast address that was assigned to more than one interface.
END
OF PART I
References:
- Members of The Cisco Learning Network at https://learningnetwork.cisco.com/welcome
- IPv6 Fundamentals: A Straightforward Approach by Rick Graziani
