I thought it would be fun to help reinforce
the concepts of ports and how they're used at the transport
layer by using Wireshark, a protocol analyzer,
to take a peek at some of the protocols,
just to verify the ports that are in use.
And in preparation for us looking at that together,
let's cover a few well-known ports for four specific
protocols--
HTTP-- the well-known port for that, at the transport layer,
is TCP port number 80--
Telnet, which is used to get remote access with a command
line interface to another system--
the well-known port for that is TCP port number 23--
DNS, which is used all the time to make a request to resolve
a name, like www.cbtnuggets.com, to an IP address
for our computer to then use--
the transport protocol and port at layer 4 for DNS requests
is UDP, as the protocol, and port number 53
for the DNS request--
and then finally, here in this list, FTP, the file transfer
protocol--
the well-known port for that is TCP port number 21.
And that's just for one component, or one piece,
of a standard FTP request.
So here, looking at a packet capture for an HTTP request--
this is entry number four--
we have the client request with a source port of 3372,
with a destination port of the well-known port of TCP 80
for HTTP services.
And what we would expect to see--
and we can find that in the very next entry, which
is entry number five--
we have a response coming back from the server
sourcing it from port 80, TCP port 80 on the server,
going back to the client's port of 3372.
Here's an example of Telnet.
So at the application layer for this entry, which
is entry number four, it shows the application layer protocol
is Telnet, and then at the transport layer,
we have TCP with a source port of 1550, chosen by the client,
going to the well-known port of the server at port 23.
And if we take a look at the next entry, which
is entry number five, we can see that the response is coming
back from the server, from port 23, going
to the client's port of 1550.
In this example, we have a DNS request.
And so with enter number one selected here, down here
in the Details pane, we have a domain name system query,
a DNS query.
And that the transport layer, we're
using UDP, which is what a DNS query uses,
the source port being 32,795, with a destination port being
53, which is the well-known port that a DNS server would
be listening on.
And if we go to the next entry here,
which is the response from the DNS server,
at the transport layer protocol, we
can see that the source port is 53,
and the destination port is 32,795.
And for our fourth example, let's take a look at FTP.
FTP uses the well-known port of 21.
And so if we look at the transport layer information,
here we have the transmission control protocol
being used at layer four.
We have a source port from the client of 1,026,
with a destination port of the well-known port for FTP of 21.
And if we take a look at the next entry
here, the one right below it, which
is the response back from the server to the client,
the source port from the server to the client
is using port 21 as a source, with a destination
port of 1,026.
In this Nugget, we've taken a look at Wireshark
to reinforce the concepts of how ports
are used at the transport layer in the TCP/IP Protocol Suite.
I hope this has been informative for you,
and I'd like to thank you for viewing.