NAT

Make the internetwork of  ptNAT1.png

The switched network has private IP network 192.168.0.0/24.
The serial link network to the ISP router is 1.1.1.0/24.

Confirm that the routers can ping each other
and the PCs can ping their default gateway.

Can the PC0 ping the ISP router:________
Of course not.  The ping Request is coming
from the 192.168.0.0 network, which the ISP router
doesn't know of (and would typically reject as
unroutable anyway because it is from a private address).
In the ISP router, turn on IP packet debugging:
  debug ip packet
then do the ping command again
What is the 's'ource of the incoming ping:_____________
What does debug say about the Reply attempt:_____________

So we need to set up NAT overload (PAT) on the NAT_R router
to rewrite outgoing packets with source IP address of
the public IP address of its link to the ISP:
  int FA0/0
    ip nat inside
  int Ser2/0
    ip nat outside
  access-list 1 permit 192.168.0.0 0.0.0.255     (or something similar)
  ip nat inside  source list 1  interface Ser0/0  overload

Output of
show ip nat translations    _______________

show ip nat statistics     is all 0

Now do one ping (ping -n 1 IP) from the PC0 to ISP router.
On the ISP router,
  What is the 's'ource of the incoming ping:_____________
  and the 'd'estination of the Reply:_____________
 so it doesn't receive anything from the private network.
On the NAT router:
  show ip nat translations      (times out rapidly)
  Inside local:__________________
  Inside global:__________________
Notice that the icmp is given a pseudo-port by NAT router.


From both PCs run the Desktop Web Browser,
URL of the ISP router.  Click Go several times.
Look on NAT router to find some examples of PAT
where the source port from the PC was rewritten
to be unique among the NAT router's source ports.