The OSI Model: Part 7 - Application Layer

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Time
15 hours 43 minutes
Difficulty
Advanced
CEU/CPE
16
Video Transcription
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>> The top layer of
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the OSI model is the application layer, Layer 7.
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At this layer, we're going to
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talk about the functionality
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and the protocols at Layer 7 but primarily,
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Layer 7 is where you really get your intelligence.
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For instance, when we talk
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about connecting from computer to computer,
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the protocols that drive
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the applications that we're using,
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those are Layer 7 protocols.
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An HTTP request,
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HTTP is Layer 7.
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Also, if you secure that HTTP request,
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that's Layer 7 as well because really,
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the underlying protocol is still HTTP.
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There are a ton of protocols up at this layer: FTP,
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TFTP, SNMP, SMTP, POP, IMAP.
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We could go on,
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and on, and on.
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Because again, these are
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the protocols where we really start the communication.
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Users begin the communication with
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an application that uses an application layer protocol.
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But when I say we really get intelligence up at
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the application layer is we
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know more than just where data's going.
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But we understand the type of
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data that's being transmitted.
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We have devices that really understand
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HTTP commands in our web browser or web server.
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We have the capability of getting
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non-repudiation by integrating with Active Directory.
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Up at the application layer,
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you have the application interaction.
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We could use an application layer firewall to block
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all users from the sales team
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from visiting sites with violent content.
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That's a high degree of intelligence,
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especially when you consider down
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>> at the physical layer,
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>> we don't even know what traffic is,
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or where it's going, or anything.
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By the time we get up to the OSI layer,
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we have protocols and
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network devices that have a
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>> high degree of intelligence.
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>> If you want to use certificate services so
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that you can get authentication and integrity,
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which gives us non-repudiation,
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that's an application layer function.
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I have to have an application that
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understands how to request for a certificate,
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how to verify a certificate,
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and how to remove
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the public key from
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the certificate and use that public key.
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When we get up to Layer 7,
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we also have content control like I just mentioned.
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An application firewall can plot data based on content.
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I can go so far as creating
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a rule that blocks images
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of the human body from being displayed,
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unless the previous query was medical in nature.
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That's a lot of intelligence,
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and we have to have
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that degree up at Layer 7 because we have
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direct knowledge and understanding of
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the contents of the messages of the data.
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Now, also at Layer 7 is we have time awareness.
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If we're thinking about blocking traffic,
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I can block traffic from 05:00
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PM to 8:00 AM because we understand time.
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Network time protocol and
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Layer 7 protocol is really important.
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Yes, for decisions like with firewalls and so on.
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But it's very important for
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synchronization of time on your systems.
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Some applications really require that synchronization.
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Kerberos, which we'll talk about in Chapter 5,
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requires synchronization of time.
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Digital forensics, having any time
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offset could be the difference
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between a conviction and an acquittal.
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We have to make sure NTP is functioning
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and there are a lot of
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application services like Kerberos,
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it could be used with mail,
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and your applications,
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and utilities that track activities.
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NTP is an application layer service.
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That's very important as well.
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As matter of fact, I was going to tell you an NTP joke,
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but my timing is always off.
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[LAUGHTER] I'll be here all week, folks.
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That wraps up Layer 7.
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We're going to continue to talk about Layer 7 services.
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As a matter of fact,
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after we wrap up the OSI model,
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which will be in just few minutes,
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we're going to go back and look at how
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firewalls help us understand the OSI model,
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and how the OSI model helps us
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understand different types of firewalls.
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