Virtual Network Concepts
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Video Transcription
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>> Hey Cybrarians, welcome back to
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the Linux+ course here at Cybrary.
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I'm your instructor, Rob Goelz.
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In today's lesson, we're going to be
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covering virtual network concepts.
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Upon completion of the lesson here,
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we're going to understand networking concepts that
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are used in virtualization and the cloud.
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We're going to determine how NAT, bridging, local,
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and dual-homed concepts are
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used and we're going to explain
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an overlay network and how overly networks
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are used in software-defined networking.
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Local networks, a host-only or local adapter
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is used in a self-contained network.
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Well, what does that mean?
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Well, what this means is that network only
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lives inside of a host system
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where the virtual machines run.
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We can have multiple virtual machines,
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but our network just lives inside of
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>> our physical system.
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>> There is no egress,
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there's no external network access.
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Why would you do this?
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Well, two reasons.
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One is for speed,
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all of the traffic is just
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traveling through physical memory on
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the host where this lives and
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security that traffic can't leave,
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can't travel out of the host
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and so we might need to do this for testing
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a security product or maybe if we're
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doing malware analysis or something like that,
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we may want to have it just locally on
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our machine and not going anywhere else.
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Now, network address translation,
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also commonly referred to as NAT,
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is set up on virtual network adapters
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and also on home networks through ISPs.
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Within that, there's only one public IP address
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that goes to the outside world.
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All of the internal address is sometimes referred to
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as private IP addresses are translated.
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When traffic is going out,
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the source address that we're
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coming from is changed to the public IP
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so it looks like it all comes from
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that same one public IP address.
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Then when traffic comes back in,
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the destination address is changed to the private IP.
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The traffic comes into the public IP address,
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and it gets changed to the private
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IP address and winds up
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on the machine on the other side
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of the network address translation.
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Now, a dual-homed system has
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an active connection in two different networks.
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Why would we do this?
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Well, there are a number of reasons.
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One is for redundancy.
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We can have it connected to two of
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the same type of networks really,
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we can aggregate the connection or have it there in
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an active-passive situation for failover,
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>> for redundancy.
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>> Or we could be trying to connect to networks.
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We can turn this host into a bridge or a proxy.
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Which brings us to the concept of bridged networks,
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flashback to Lesson 3.9,
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where we talked about bridging.
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A Linux system that's connected to
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>> two separate networks,
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>> can be configured as a bridge and a
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>> bridged adapter makes
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>> a virtual machine look like
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any other system on a non-virtual network.
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It gets an IP address in the same sub-net and it can be
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seen on that network by
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any other systems that are living on the network.
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Now the last concept we're going to talk
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about here is a little bit difficult.
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We're going to go slow through this.
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An overlay network is what is
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used in software-defined networking and what that is,
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is we just start layering
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one network on top of the other.
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SDN allows applications and
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software to control network infrastructure.
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Software-defined
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networking controls the network information.
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We generally just have a dumb switch and then we
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use software-defined networking to program the switch
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to set it up to have maybe virtual switch or we
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could change it into being a gateway or a router.
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An SDN has a controller program and is seen
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as a logical switch in most cases.
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An overlay network is simply a method of
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network virtualization.
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That's what we're talking about here.
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It's a type of virtualization specific to
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networking and it is used in an SDN.
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What we see with this is that networks are
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split into separate channels and then
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packets are encapsulated like our pills
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here and sent through a tunnel channel.
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Underlying network hardware is just a carrier.
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Like I said, the switches are done,
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they're just providing electronics really.
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They don't know what's being sent across it,
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all that is managed in software.
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In this lesson, we covered
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network concepts used in virtualization.
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We talked about how NAT, bridging, local,
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and dual-homed networks and concepts are used.
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Then finally we covered
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overlay networks and how they work at a high level.
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Thanks so much for being here and I look forward
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to seeing you in our next lesson.
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