Hey guys! It's Clint Garrett Ace Networker and I want to welcome you to this video
where we're going to be talking about bridging versus switching and why we
used to use bridges and why we now use switches on computer networks. Now,
this is the first video. I'm going to be going through a long series just talking about network
switches and when we're done with that series when we've gone into some in-depth detail about network
switches and how they work to get you up to date on being able to pass the Network+ exam (at least,
probably better, maybe the next certification like CCNA or CCNP perhaps, we'll see)
we're going to get you up to that level and we're going to go through this series on switching
and once we're done with switching we'll then move into routing. So with this first video
we're going to talk about bridging versus switching, why bridges are seldom if ever
used anymore on computer networks, why we use switches and why we have what we call multi-layer
switches. Now some Layer 3 or Layer 4 (they call them) switches can actually function much like a
router on a smaller to medium-sized network. So let's get into bridging versus switching.
To begin our exciting journey into the world of network switches and switching
on computer networks, we have to first go back into really recent history
okay we're not talking about that much history. We're not getting that
in depth. We're just talking about 30 years ago three decades in most cases when you're
talking about I/T it advances so fast that really you're just talking about a few years
or in a lot of cases when you're talking about a lot of different technologies,
you're talking about just a few months. So we're going to focus on bridging versus switching
in this short video but to understand bridging we have to go back a little bit in the history of I/T
to why bridges were developed and used. And to understand that we have to show how hubs
originated and were used and I'm going to go over that history really quickly and really fast here
so we can immediately get to where we are now with technology. Now if you haven't watched it,
you're welcome to watch this video on hubs and how they actually work and why you don't really find
them used on networks in the present day. Real quick, in the early days of computer networks you
would have what were called mainframe computers. You would then have controllers connected to these
mainframes and off of those controllers you would have dumb terminals (they used to call them dumb
terminals) these were where the end user or users would actually access that mainframe computer
and everything on it. And a dumb terminal really was just a monitor, a keyboard, a mouse and just
enough equipment to communicate with that mainframe over that connection. Unlike the
PCs that we have now. Now it's important to understand these mainframe setups because
at the time to allow remote sites to connect to the mainframe computer they would need
bridges. And it's important here that you get that this is where the network bridge was originally
developed and used. I'll come back to bridges shortly coming up here. So, eventually that
mainframe setup morphed into what we now refer to as a collapsed backbone network like the one shown
here. It was called a "collapsed backbone" network because hubs were developed and used to connect
PCs, which were quickly on the rise in stardom in fame and stardom at the time. To connect these PCs
directly to the corporate backbone they would use these hubs. They would connect these PCs to the
corporate backbone to reach any network servers or other services, devices on that network. Again, if
you watch the video I created on hubs, you'll see why they couldn't keep up with the demands for use
that we humans require of computers and networks, especially by today's standards. And really, these
days, I'm not trying to be cruel or anything but hubs these days on today's networks with demands
that are needed on today's networks are about this useful... But hubs were used at the time because
they were the only thing available for connecting multiple PCs to a computer network at the same
time. There's also a lot of history on how the servers on those early collapsed backbone networks
ran off of token ring connections and didn't function like netware servers do now, and I may
create a video talking more about the history of those technologies too in the near future. Suffice
it to say you don't need to know all of this history to pass the Network+ certification exam,
at least not yet. The key thing to keep in mind about these corporate collapsed backbone networks
is that they grew and grew and grew and as they did, network services became slower and slower.
This is very similar to congestion of traffic in major cities. When you look at a major city and
you have major traffic congestion, if all you had were major freeways like when you just have
big routers and then they have to immediately exit off into a neighborhood you don't have something
in between so that's where switches will come into play. There are multiple reasons this happened.
The biggest of those was that land services were needing faster service, software demands from new
and innovative software applications needed more bandwidth and usage by themselves, and networks
were becoming saturated and bogged down. This is where bridges come back on the scene. Bridges
were used to break up collision domains to help handle that saturation that was occurring on those
networks. However there were some limitations: Bridges have a limited number of physical ports
for use on their physical hardware and bridges cannot provide the network services needed to
handle everything. Layer 2 switches helped save the day by breaking up collision domains on the
network into a separate collision domain for each port (each physical port) on the switch. The real
benefit to Layer 2 switches arriving on the scene was that they could provide hundreds of ports
instead of the limited number of ports available on bridges or on a bridge. So those early networks
began to morph into something like this. You would have hubs connected on each port of a switch to
allow more devices (typically PCs in most cases) but this would allow more devices to connect in
each area of the network and that's the first and primary way that Layer 2 switches started being
used to solve the problem of ever larger growing networks and saturation of those networks. Now
this leads us to the other big reason why Layer 2 switches replaced bridges on computer networks.
Bridges were designed to use software to create and manage a filter table in their own memory
for making decisions about network traffic that arrived on their physical ports. Layer 2 switches
on the other hand used ASICs. That acronym stands for Application Specific Integrated Circuits.
Layer 2 switches use ASICs to create and manage their filter tables. Now I'll stop right here
and remind you that it's still okay to think of a Layer 2 switch or Layer 2 switches as
multi-port bridges. That's because they both break up collision domains.
But the efficiency of Layer 2 switches compared to bridges and the fact that switches offer a
lot more physical ports for connecting devices than bridges do, shows why switches won out over
bridges and still do to this day. I also want to inject here that Layer 2 switches and bridges are
much faster than routers when we get into those in later videos, because switches and bridges
don't have to examine the network layer header information at the beginning of a packet inside
each frame. They simply look at the frame header Source and Destination MAD addresses and then make
decisions to either forward the entire frame or drop it based on that information. Last
but certainly not least is the fact that both bridges and switches could use the loop
prevention protocol known as spanning tree or spanning tree protocol. But the real key here
is that only one instance of spanning tree can be used on a bridge, whereas multiple instances
of spanning tree protocol better known as STP can be used, multiple instances can be used on
a Layer 2 switch. I'll get more into detail about spanning tree as we go along. In fact,
if you haven't watched this video yet I'd invite you to watch it where it talks about
what spanning tree is and why you have to have a loop prevention protocol like spanning tree to
prevent your entire network from locking up and no longer passing any traffic, because that is a
possibility if you don't have a loop prevention protocol like spanning tree running. Remember
that bridges are software-based while switches are hardware-based (they use the ASIC chips to
make their forwarding decisions on a switch). Also remember that a switch can really be thought of as
a more-capable multi-port bridge. You can have a lot more physical port connections on a switch
than you ever did with a bridge. Remember that bridges can only run one instance of spanning
tree protocol while switches can typically run multiple instances of spanning tree protocol.
Remember that bridges and switches forward Layer 2 broadcasts, and I'll get more into broadcasts
in future videos, so we'll go over those. Bridges and switches learn MAC addresses from the Source
address on each frame that arrives on an inbound port. And really last but not least is that fact
that bridges and switches both make forwarding decisions based on Layer 2 addresses. So that
summarizes the differences between bridging versus switching and it's the perfect intro video for us
getting into switching and talking about network switches and the Layer 2 level of the OSI model,
because Layer 2 is typically where you're dealing with Local Area Networks and keeping everything
local on a Local Area Network. So the technologies that are involved in this series I'm probably
going to get into a little bit more depth about switches and switching and Layer 2 technologies
on computer networks than what is required of you in a Network+ exam certification setting, but
I want you to be more than prepared. So what I'm doing is I'm going to be going through a series
that will really kind of get you up to a CCNA level certification, okay? So with that said,
thank you so much for watching and I will see you in the next video...