- [Narrator] There are some key differences
in an IPv6 header.
So let's go ahead and take a look at our IPv4 header again.
First you must remember an IPv4 header format
can vary in length.
IPv6 does not.
This is 20 octets in length
compared to IPv6's minimal 40 octets
compared to how large that address space is.
Now we want to remember a couple things.
We have our total length, our type of service,
our protocol field which defines
who owns this data we're carrying.
Time to live field and our source and destination address.
We also have a fragment offset
because we're going to possibly fragment our IPv4 headers.
Now the basic IPv6 header contains eight fields,
making it only twice as large as an IP header
at only 40 bytes.
Right. Now remember, this could not vary,
so it's more efficient.
Now, so which header do you think, by looking at this,
is equivalent to the time to live field?
Well remember the time to live field in IP version four,
told us how many routers we went through
or what was considered hops.
So this is now called the hop limit,
which was called our time to live.
In IP version four, we fragmented traffic
and had a fragmentation field.
In IP version six, we use the extension header
for our fragmentation and we need to remember that.
Now for our protocol field that was in IP version four,
we still have to know what we're carrying
and that's called the next header.
So in other words, what's the next protocol
this is going to be handed to.
So just remember our IPv6 header is only twice as large
as an IPv4 header but more efficient.
Now the three things I discuss here, the three fields,
hop limit, next header and extension header
are your CCENT and objectives that you need to know.
So let's go ahead and summarize these
and understand why IPv6 header is simpler
than an IP version four header.
So unlike IPv4 headers, IPv6 headers have a fixed length.
IPv6 uses an extension header
instead of the IPv4 fragmentation field
and lastly, IPv6 headers eliminate the checksum field
that IP version four used in its header.