>> Our next section is on protocols and port numbers,
and this is a big portion of the exam.
You've just spent some time going through
the OSI model and the TCP/IP model.
We've talked about the fact that TCP/IP is really
a protocol suite with lots of
different protocols that make up the suite.
Each one of those protocols has
a port number assigned to them.
A port number is a software Identifier slot.
When the traffic gets to your system,
your system knows which application or
service is needed in order to process the traffic.
With your port numbers,
there's an endpoint for communication.
They're not a physical port
>> that you plug something into,
>> but they are conceptual entryway into the system.
When one system is going to connect to
another system via the network,
they have a conceptual port number.
Now, with your port numbers,
there are what are referred to as well-known ports,
which is mostly what we're going to work with.
The idea is that all of
these protocols that we're
>> going to talk about in class,
>> these application layer protocols
and application layer services,
all have ports that are assigned
to them so that, by default,
web traffic is port 80,
DNS traffic is port 53, and so on.
With these well-known port numbers,
you have to remember from 0-1,023 of the port numbers.
I just wanted to see who was listening there.
You don't have to memorize 1,023 port numbers,
but there are about 20 that you
just need to know really well.
There'll be a lot of port questions
on the exam and hopefully,
some of you guys will stick around for
the security ports exam as well.
You have to know your port numbers on that exam too,
so you might as well memorize with a smile
because these will come up multiple times.
For your registered port numbers,
vendors will register a certain sort of
proprietary services or software with IANA,
which is the organization that manages port numbers.
These are the ones that are reserved because
they're used specifically by vendors.
There are dynamic ports from
49,152 all the way up to 65,535.
These are referred to as ephemeral ports.
These are temporary ports that
aren't assigned to anything particular,
but that can be used in order
to indicate some connection.
It's often used as a source port number.
When computer A connects to computer B,
the destination IP address is
going to be computer B's IP address,
and whatever service, for example,
web server computer B port 80.
What's also on the data packet is
the source address and a source port.
A source port is an arbitrary number,
usually over 49,152.
Ultimately, that's a way of
identifying when traffic comes back into the network.
It's often used with network address translation,
so when we talk about ports to memorize,
I want you to focus on the well-known ports.
I'll give you a list of following this section.
For registered ports, know what the range is
and other for the vendors and proprietary things.
For a dynamic ports,
again, we are not worried too much about specifics,
for your own knowledge,
know that source ports are pulled from that range.