In this video from ITFreeTraining I will have a look at ISATAP. ISATAP is an IPv6 transition
technology. This technology is used to allow IPv4 only and IPv6 only networks to communicate
with each other.
ISATAP stands for Intra-Site Automatic tunnel address protocol. The first exam hint you
should take away from this is the word intra. Intra, meaning internal network, so ISATAP
was essentially designed to work within a site or an internal network. This means it
is not used for communication on the public internet. If you see an exam question on ISATAP,
eliminate any answers that do not relate to internal use.
ISATAP, put in the simplest way, connects an IPv4 only network to an IPv6 only network.
To illustrate this, consider an IPv4 only network and IPv6 only network. There is no
common protocol between the two networks; however, if an ISATAP router is placed between
the networks, the networks can now communicate with each other. ISATAP works as a bridge
between the two networks. Let’s have a look at how this is achieved.
To achieve this, an IPv4 node creates a tunnel to the ISATAP router. This tunnel is assigned
an IPv6 address. The IPv6 address of the tunnel is broken down into two parts. The prefix
part is provided by the administrator. This can be any valid IPv6 prefix. This is used
for routing on the IPv6 network and send data to the ISATAP router.
The second part of the address is the interface ID. The interface ID has the IPv4 address
encapsulated in it. The interface always starts with the same hexadecimal sequence followed
by the IPv4 address. When looking at the address, sometimes the IPv4 part of the address will
be shown as an IPv4 address and other times the address will be shown in hexadecimal.
To understand the ISATAP transition technology, I will look at a different example. ISATAP
uses tunneling to transfer data from the IPv4 host to the ISATAP router. This essentially
means that the IPv6 packet is placed in an IPv4 packet.
To understand this, consider an IPv4 only network with an IPv4 only computer on it.
This computer wants to communicate with a computer on the IPv6 only network. To do this,
the computer creates an IPv6 packet. The computer however is not on an IPv6 network, so in order
to transmit the packet, the IPv6 packet needs to be encased in an IPv4 packet.
In the next step, the packet is sent via an ISATAP tunnel to the ISATAP router. This example
is a simple one, but the packet could have traveled over many IPv4 routers to get to
the ISATAP router. Once the packet reaches the ISATAP router, the IPv4 packet is discarded
leaving the IPv6 packet. This packet is then sent on the IPv6 network to its destination.
This is a simple example, but shows the basic process involved. I think you are ready for
it, so let’s look at a more difficult example which shows all the steps.
In this example, a computer is connected to an IPv4 network. The computer is allocated
an IPv4 address on this network. The computer wants to contact another computer which is
on an IPv6 only network with an IPv6 address. There is no common protocol connecting both
computers so ISATAP will be used here to bridge both networks.
In order to do this, the IPv4 computer will allocate itself an IPv6 address by contacting
the ISATAP server. The first part of the address is the network prefix, which is configured
by the administrator or obtained from the ISATAP server. The interface ID part of the
address starts with 5efe followed by the IPv4 address of the computer.
The computer now has an IPv6 address. However, it is connected to an IPv4 network. This is
where the transition protocol comes into play. First of all, the computer needs to locate
an ISATAP router. This can be manually configured, but in this case, the computer will contact
a DNS server to obtain the address of the ISATAP router.
The computer then creates an IPv6 packet. Notice the source address is the address that
it allocated to the computer using ISATAP and the destination is the address of the
IPv6 computer. Since the computer is on an IPv4 only network, the IPv6 packet will be
placed in an IPv4 packet. Notice that the source IP address is the local computer’s
address and the destination address is the address of the ISATAP router.
In order to contact the IPv6 computer, the IPv4 packet will be transmitted across the
network. Since it is an IPv4 packet, it will be routed like any other IPv4 packet until
it reaches the ISATAP router. When it reaches the ISATAP router, the IPv4 packet is removed
and the IPv6 packet is routed to the destination like any other packet. If the IPv6 computer
wants to contact the IPv4 computer, the process is simply reversed.
You can see how the ISATAP process works, providing a bridge from IPv4 only networks
to IPv6 only networks. However, remember that ISATAP is designed to work inside an organization
on its private network.
Thanks for watching this video on ISATAP. In the next video I will look at what is
required in order to set up and use ISATAP. Until that video, I would like to thank you
for watching.