In this video I'm going to show you how to set up and not overloading or port address translation or
pat these two internal devices Route 1 and of for a going to be enacted to the IP address of router
to the router to configure it on the first East and a 0 1 interface with the IP address.
8. wondered wondered one but rather than allocating additional addresses for Nat I'm going to Knecht
both these devices to that single IP address by using port address translational Pat router 3 in this
example is acting as an Internet server on the outside at the moment.
Radu one is not able to ping router three out of four on the inside over here is also not able to ping
rotisserie.
The pings are failing
and that's because there is no routing enabled on Rodda 3.
It only has a directly connected network.
It doesn't know how to send traffic back to those devices.
We can see that by running debug debug IP ICMP debug IP packet I'll do a ping from a one to router three
again.
We can see messages here unrideable unrideable.
So the traffic is getting from the internal hosts to the outside device.
Robert 3 but rotisserie doesn't know how to route it back again because the ping is being received from
10 1 1 1 so the local router is trying to send an echo reply back to that address but doesn't know how
to get to that address because there is no rot in the writing table.
To get router three to 10 one one one so neither Route 1 or rod of four are able to ping Rodda three.
So let's enable that on rockety.
So interface if 0 1 IP not outside.
Now in this example we need to make an important distinction to the previous net examples in this example
I am netting multiple devices to the same IP address on router 2 and that IP address is configured on.
Ethan it is 0 1 so we are not allocating a missional IP addresses to Nat.
This is probably the most common way of doing NAT in the real world.
So Notice I'm using the term Nat and that's what most engineers will call it.
But in actual fact it's Pat or port address translation or Knecht overloading because we taking multiple
devices and overloading a single IP address to allow those devices to use that single IP address for
access to the Internet.
So what I've done thus far is enable Nat on the outside here and enable that on the inside of car.
That's all I've done and I'm going to type IP Nat and I'm netting the inside devices.
And in this case they source addresses based on an access list which I'll create in a moment access
list one and I'm going to enact them to a physical interface first.
Ethan it is 0 1 rather than allocating a separate IP address.
And this is the important piece I'm going to overload this next entry to allow multiple devices to access
the internet using that single address.
I have to create to the access list one as referenced in my command access list one permit and who's
going to be allowed to be nattered
made a mistake.
In this case it should be anyone in the 10 1 1 0 network.
So anyone in this network will be nattered so show i.p that translation.
No not translations at the moment.
I'm going to enable Telenet on rotisserie
and a of one I'll do a telnet to router three.
But before I do that let's enable not debugging on router too so we can see the net debugging in real
time.
Telnet eight hundred one to two hit enter notice we can see the net translations taking place the source
IP address 10 one on 1 is being netted 2 8 1 1 1 the IP address for traffic S. 2 8 1 1 2 the reply comes
back.
So Source 8 1 1 2 sending traffic 2 8 2 1 1 1.
That is not to add 2 10 1 1 1 so I put my post-wedding of Cisco.
We can see the translations taking place type a single character.
There's the net translations show IP net translations.
There's the dynamic net translation notice inside a local address 10 1 1 1.
Using this ephemeral or random port number is being translated to 8 1 1 1 using the same port number
going to 8 1 1 2 on port 23.
So notice rotisseries not being translated but the entries for that address are shown in the table.
Let's do a nother telnet so from Rotto 4 to 8 1 1 2
and log in we can see 10 1 1 for this is not a full IP address is translated to 8 1 1 1 router TOS IP
address for traffic going to 8 1 1 2 roaded 3s IP address show IP net translations we can see two dynamic
and net translations one for 10 1 1 4 and 1 for 10 1 1 1.
And this is how rodded to knows that the traffic is destined to win both Rodda 104 telnetting throughout
history rotatory since traffic back to rodder too.
But based on different port numbers and on router 3 Alceste type one character in noticed we could see
sequence numbers here.
Try type another character notice 2 8 8 3 2 2 8 8 3 3 3 4 3 5.
And then for the return traffic we can see the sequence numbers as well.
Show IP net translations there are translations once again what's important to remember is that when
traffic is returned from rotatory to rodded to it's coming from the address 8 1 1 to port 23 going to
this address 8 1 1 1.
But using a port number so so rodded too is able to differentiate between the two sessions based on
the port number.
Hence the term port address translation when traffic arrives from rotisserie at rodded to with a destination
port number of the US going to eight triple one.
The traffic is going to be forwarded to Route 1.
But when it arrives going to the same IP address.
But this port number the traffic is forwarded to router for router to ensures that these port numbers
are unique in the next table.