From IPv4 Private to Public Addresses

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來自 Cisco 的課程

Data Communications and Network Services

285 個評分

Cisco

Data Communications and Network Services

285 個評分

課程 3（共 5 門，Specialization Cisco Networking Basics）

Welcome to the third of five courses in the Cisco Networking Basics Specialization. Now that you know the basics of what an network is and how the devices on a network communicate with each other, it is time to explore the network further. In this course, you will learn the benefits and limitations of the IPv4 addressing system and why NAT and IPv6 were implemented to address the limitations. You will also explore common network services and protocols such as email, web services, instant messaging, DNS, HTTP, HTML, SMTP, Telnet, and SSH. At the end of this course, you will be able to: 1. Describe the role of network services including DHCP and DNS. 2. Use Cisco Packet Tracer to configure a router to perform DHCP services for a LAN. 3. Explain use of IPv4 private addresses with NAT. 4. Compare TCP and UDP protocol operations for efficiency and reliability. 5. Describe the network services and applications for file transfer, web access, email, remote access and instant messaging. 6. Observe how web requests are processed by the web client and the server. 7. Use various tools to verify network operations.

從本節課中

Limitations of IPv4 and Transitioning to IPv6

In this module, you learn the benefits and limitations of the IPv4 addressing system and why NAT and IPv6 were implemented to address the limitations. You will use Packet Tracer to create and examine traffic for NAT translations.

From IPv4 Private to Public Addresses6:51

與講師見面

Telethia Willis
Cisco Networking Learning & Development

- In this lesson, we're going to talk about private

IP networks, and the need for network address translation

when we go from a privately addressed network

to a publicly addressed network.

IP addresses have, IPv4 addresses, have two categories.

The first one is private addressing.

Private addressing is addresses that

can be used within an organization.

They work perfectly well.

You can assign them to hosts.

They can be routed between different networks.

But when you need to go outside of your organization,

across the publicly addressed Internet,

you have to have a registered public IP address.

Now, the people who designed IP reserved certain networks

that you could use them within your enterprise,

but they will not route across the Internet.

Those addresses are 192.168, 172.16, and 10.

Now, most of you who have a home network,

if you look at what the IP addresses are that are

assigned to your various devices, you will find

that usually they are assigned to the 192.168 network.

The reason being is that it uses a subnet mask of 24 bits,

which only leaves eight bits for host addressing.

Those eight bits only have 254 possible host addresses.

So, they're used for smaller

organizations and smaller networks.

172.16 now uses 16 bits as identifying the network portion.

So you can have many more,

and 10, it only uses eight bits for the network portion.

So it's used primarily for very large enterprises.

Now, if we have a network addressed with private addressing,

as we do in our little organization here,

we would have difficulty sending this traffic

out to a server that is located on the Internet.

The Internet will only route

registered, public IP addresses.

So, 192.168 does not fall into that category.

So, a function was developed

called network address translation.

In network address translation, a private addressed host

can actually send traffic across the Internet,

and the manner in which it does this is that the router,

and you can see here is our router that connects us

to the Internet, and also to our two privately addressed

networks, the router performs a function that keeps

a table in which 192.168.2.1 is actually represented

on the Internet with a publicly registered address,

and we'll say that it's in the same network here.

So, it's 200.100.58.50, and then if my host here decides

also to communicate with a device out on the Internet,

it would be added in the table,

and assigned another registered address.

So, to hosts out on the Internet,

I am represented by this registered address.

So when my packet goes out my network,

so it leaves me, when it comes up here,

the source address is my privately assigned address,

192.168.1.15, and the destination address in my packet

would be the 210.100.5.5 address of the destination server.

When it comes up here, the router looks at its network

address translation table, and sees that I will be

represented on the Internet by this address.

So, it changes the packet, my little packet here.

When it leaves the packet then looks like

the source address of 200.100.58.51,

and the destination address of 210.100.5.5.

So when the packet actually reaches the server,

the server will send its response back to my registered

address that was assigned to me here.

So it'll address its packet with the source 210.100.5.5,

and the destination address of my registered address,

200.100.58.51.

This packet will make its way back to my router,

and my router will see 200.100.58.51,

and it will say who has that address assigned to it?

And it will look in its table,

and it will see that that address is assigned to me.

So it will change the packet back to show my local address

as being the destination and then it will

forward it back out to me.

So I will happily get the packet from the server,

and be able to display the webpage.

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