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Now analogies are okay but it's much better to demonstrate this practically using Packet Tracer.
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So let's actually build a network together and I'll show you how clients and service can work together
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and I'll show you that a client can also become a server.
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You could have two laptops one providing a service to another laptop so the laptop can be a server in
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some cases or it can be a client.
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In other cases.
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Okay.
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So in packet trace I'm going to go to end devices and I'm going to select a server and add it to my
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topology.
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I'll select a traditional P.C. and add it to the topology.
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Now these are symbols or representations of devices physically.
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This is a server physically that's a laptop.
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But logically that's what they look like.
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These are once again just symbols in an application like Packet Tracer in networking we use network
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diagrams to explain what a network looks like.
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Another example would be here where I'm using an application called Genius 3.
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So here's a Windows Server and here's a P.C..
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Notice different symbols for different types of devices.
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I could change the symbol if I wanted to.
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So in this application I simply select a change symbol and then I could specify a nother type of symbol
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to represent a device.
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I notice there are many types of devices shown here but as an example I could say this is a server cluster.
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If it was a cluster of service.
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The point is is that a symbol is simply a logical representation for a physical device in Packet Tracer.
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If I click on this server there's a physical representation of the server and then I could once again
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change the symbol or icon used to represent that server
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here's the physical representation of the P.C. notice.
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Ethan it pulled right over there.
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So again this is a logical representation of a device.
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Now these two devices can communicate with each other.
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We either need to communicate using a physical cable or we need to communicate using the air.
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So what I'm going to do is select connections and I'll select what's called a crossover cable a crossover
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cable allows two pieces to talk directly to each other in the old days we had to use what was called
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a crossover cable to allow P.C. to talk to P.C..
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Now today we don't have to do that.
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I'll discuss order MDI X late in the course.
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This used to be a problem in the old days it's not such a problem these days notice the interfaces have
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gone green but in packet trace if I delete that cable and then use just a standard ethernet cable
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notice the interface is down because Packet Tracer still expects you to use the right cable.
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So once again I'll delete that cable and I'll select a cross over cable copper crossover cable and connect
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fast ethernet on the P.C. to fast ethernet on the server.
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So there you go.
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I've built a network.
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That's an example of a network.
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It's a logical representation of a physical network.
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OK.
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But to allow these two devices to communicate with each other we need to have two things we need to
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have an ethernet address or MAC address that's pre-built into network interface codes.
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So a manufacturer will burn a MAC address onto a network interface code.
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You can change MAC addresses but generally you don't have to.
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They are globally unique.
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There have been cases where there have been duplicate MAC addresses but in general that isn't a problem.
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Every device has its own MAC address.
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So if I look at this P.C. and go to config go to foster Ethernet zero.
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Here is the MAC address of the P.C. you can see your mac address on a Windows computer as an example
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by going to control panel network and Internet network and sharing center.
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Have a look at your Adapter Settings.
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So as an example this Wi-Fi network adapter has this MAC address.
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That's its physical address or MAC address.
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You'll see something similar on an iPhone or other devices.
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Every device that communicates on physical Ethernet or communicates on Wi-Fi is gonna have a mac address
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we don't have to configure that again that's configured by default by the manufacturer on the server
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first Ethernet zero notice she has the MAC address of the server but what I'll do is change that so
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I'll change the MAC address.
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This is a twelve digit number in hexadecimal.
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Now I'll discuss hexadecimal and the details of this later in the course but for the moment just notice
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there are 12 numbers there hexadecimal numbers.
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So that's the MAC address now of the server.
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On the P.C. I'll change the MAC address as well and I'll make this a bunch of ones so triple 0 1 followed
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by eight ones.
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Now again you don't have to change the MAC address.
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I'm just doing that to make things simple now the second thing we need is an IP address typically in
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networks a server which could be a home router we'll be allocating IP addresses to your pieces using
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a protocol called Dynamic Host Configuration Protocol or DHEA P.
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So D.H. C.P. is allocating IP addresses to your P.C. P.S. I can see that here by opening up a command
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prompt and if I type IP config an IP address in this case IP version 4 is configured on my Windows laptop
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so those windows laptop has received an IP address automatically from a DHB server or it could be configured
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statically you can configure IP addresses statically in our little network.
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We don't have a router or another type of device so we have to manually configure the IP addresses.
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So on this first P.C. I'm gonna give it an IP address of tendered wandered wandered 1 and a subnet mask
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of 255 255 255 dot 0.
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Don't worry too much about IP addresses for the moment just understand that we've figured a MAC address
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you don't have to do that and I've configured an IP address.
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You don't have to do that if you've got two Windows laptops they can automatically communicate with
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one another here because of using Packet Tracer.
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I'm configuring the IP addresses manually Okay so if I go a desktop and open up a command prompt I'll
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make this a bit bigger and top the command IP config.
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What you'll notice is this P.C. has an IP address.
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I'll do something similar on the server.
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Let's give the server ip address of 10 dot wondered one to two and a subnet mask of 2 4 5 2 4 5 2 4
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5 0.
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So on the P.C. now I can use a special application called Ping to verify connectivity to the server.
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Ping is basically sending a message saying hello are you there.
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And then the servers replying back yes I'm here and the IS SAYING HELLO ARE YOU THERE.
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AND THE SERVER replies back yes I'm here.
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So basically it sends the he sends a message to the server saying Please reply if you're there and the
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server replies back saying Yes I'm here and it's used just to verify that the server is up is it there
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is it working is it turned on so on the P.C. I can use the command ping 10 1 1 2 and as you can see
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there we are getting a reply from 10 1 1 2 the pieces IP addresses this the servers IP address
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use the come on IP conflict to see it make this bigger is 10 1 1 2 Okay but that doesn't really prove
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anything except that my P.C. can ping the server that I've got IP connectivity to the server I basically
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sent a message to the server saying Are you there and the server reply back saying Yes I'm here.
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So this server is there but that doesn't really help us what we want to do is have a look at the services
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running on the server and notice here are a whole bunch of services we've got HDP as an example we've
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got DNS which is domain name system basically allows me to resolve domain names such as Google dot com
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or Facebook dot com to an IP address we've got other types of services here like email FCP and various
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other services.
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So on the HP Service I'm going to leave this on that's the default on the P.C. if I close this command
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prompt down and open up a web browser and deletes bras using HDP Hypertext Transfer Protocol to the
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IP address of the server.
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What you'll notice is a web page displays I can see a small Web page here which says hello world.
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I can go back I can go look at an image page and he has a Cisco logo.
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Now that doesn't really do much but that's an example of a network.
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We've got a client on the left a server on the right.
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The server is configured with the HP Service and it's serving a web page to the client when the client
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requested the web page.
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If I turn the service off so I've turned it off now for HDP but it's on for HDP s HDP has once again
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just an encrypted version of hypertext transfer protocol which is used for web browsing.
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I'll close this down open it up again try and go to HDP 10 dot wandered one dot too.
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Now what will happen and it might take it a while is it will time out and there you go.
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Notice it says request timed out and that's because the server is no longer listening on port 80.
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It's not listening.
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So it just basically drops the traffic that you send to it.
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So view Senator request saying show me a web page on port 80.
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It just basically drops the request ignores what you what you're asking.
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If I go HDP s however notice we get to the web page because the server is listening on Port 443 now
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which is the port number used for HDP s of enable HDP once again.
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And let's try and go to the server on port 80 and that's worked.
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So just to prove it because that wasn't very clear I'll open up a web browser again and manually type
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HDP tendered wandered 1 to 2 and notice the web page displays.
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Now another great thing about packet tracer is we've got the simulation mode.
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If I select a simulation mode I can actually see what's going on.
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So on the P.C. and I'll just move this around so we can see what's going on.
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I'm gonna click Go now and what you'll notice is a packet has been sent into the network.
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Now there's a lot of information here and I'll go through this in more detail when we talk about the
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OSA model and the TCB IP model.
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But what I'd like you to see is we've got a mac address which is the MAC address of the P.C. sending
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traffic to the MAC address of the server and we've got an IP address which is the IP address of the
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P.C. going to the IP address of the server source IP addresses P.C. destination IP address is the server
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at least to here we've got an ether net had a source MAC addresses the P.C. destination MAC address
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is the server.
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Notice here we've got port 80 port 80 once again is the port number that the server is listening on.
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If we look at that in more detail and don't get scared by this.
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This is just an example of the kind of data that's sent into the network.
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Why shock.
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We'll show you this in more detail than this but this gives you an idea of what's going on.
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Source MAC address is the P.C. destination MAC address is the server we've got source IP address P.C.
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destination ip addresses the server we're using IP version for here we're also using a protocol called
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TTP or transfer control protocol that basically just gives us reliability in a network transmission.
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So if you sent something to a server and it gets lost it'll be reset re transmitted.
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So it gives us reliability.
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Destination Port number is 80.
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So when we send that into the network that will be sent to the server and the server will receive that.
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And then what it will do is send something back to the P.C.
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so a packet gets sent back from the server to the P.C. with information.
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Notice the source port for the reverse traffic from the server to the P.C. is 80.
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Basically the client talks to serve on port 80 and then the server replies back from port 80 to a port
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number that your client has randomly decided to use.
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Now that's a lot of information and I'm hoping it's not too overwhelming the best thing you can do is
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install packet tracer and build a topology yourself and follow what I'm doing.
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There's no better way to learn than to do things yourself.
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One of my favorite analogies is riding a bicycle.
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I can talk about riding a bicycle.
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I can show you pictures videos etc but until you yourself ride a bicycle fall off a few times struggle
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a bit you'll never learn to ride a bicycle.
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Best way to learn is to just do it so bold as yourself and try it yourself.
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