In the previous video, we have done configuring BGP on google and ISP. 2
Next in this video, we are going to learn about the concept of network address translation. 3
But before that, let’s remember about private and public ip address first. 4
Public ip address is in the internet and accessible from anywhere, but private ip address is only 5
accessible from the local network. 6
In this topology, let’s say the Ip address of google server, the network between google 7
and ISP, and the network between ISP and customer is public ip address. 8
And then the ip address of vlan 10 and vlan 20 is private ip address. 9
The problem is, private ip address will not able to go to the internet, so for example 10
here from vlan 10 want to ping to google, so the source address is 192.168.10.2, 11
let's say this is the ip address of pc 0, and then the destination will be the google, 12
which is 172.16.10.2. 13
When pc 0 send this packet, the packet will go through router 3, and then forwarded to ISP. 14
ISP will see the packet, here ISP will see that the source address of the packet is 192.168.10.2, 15
ISP don’t know about this network, because this is private ip address, 16
so the packet will not forwarded to the internet or google. 17
So for now, the client will not able to communicate with internet or google. 18
So the solution is, we will configure nat in the customer router. 19
The function of nat is to translate the network address, in this case nat will translate the 20
source address. 21
So if the source is 192.168.10.2, after nat process in router 3, the source address will 22
become the public ip address of customer router, which is 10.20.20.2 23
After that, the packet will forwarded to the ISP, ISP will see the packet, 24
now the source address is public ip address, and ISP know about this ip address, so the packet will 25
be forwarded to the internet. 26
Okay so that is the concept of network address translation, I hope you understand. 27
I think enough for this video, in the next video, we are going to configure nat 28
so all client will able to communicate with internet or google. 29
Thank you for watching and see you on the next video .