This is an Updated CCNA exam question (2015). You might see a different IP addressing, Port allocation and Configurations.
As usual, take time and read through the question (thrice if possible) so as to clearly understand what the question is all about.
Note: This NAT SIM LAB are used for demonstration only, you might come across a slightly different IP addressing, Port allocation in the real CCNA exam. But it all works the same way if you could just grasp the technique.
I suggest you use packet tracer for practice.
Use the network simulation topology below to answer the following question.
A network administrator is configuring a router for the HQBR company to provide internet access. The ISP has provided the company six public IP addresses of 198.18.184.105 198.18.184.110. The company has 14 hosts that need to access the internet simultaneously. The hosts in the company LAN have been assigned private space addresses in the range of 192.168.100.17 – 192.168.100.30.
The company has 14 hosts that need to access the internet simultaneously but were issued with just 6 public IP addresses from 198.18.184.105 to 198.18.184.110/29. To accomplish this we use NAT overload or PAT (Port address Translation )
Double click on the HQBR router to access the CLI
Use the following command:
1. Change the router’s or host name to HQBR
2. Create a NAT pool of global IP addresses to be assigned
HQBR(config)#ip nat pool mypool 198.18.184.105 198.18.184.110 netmask 255.255.255.248
(/29 is the prefix of 248) see the cram table:
3. Create a standard access control list that permits the addresses that are to be translated.
HQBR(config)#access-list 1 permit 192.168.100.16 0.0.0.15
(0.0.0.15 is the wildcard mask of 240 or prefix /28)
Read more on wildcard mask explained
4.Establish dynamic source translation, specifying the access list that was created.
HQBR(config)#ip nat inside source list 1 pool mypool overload
The above command translates all source addresses that are permited by the access list 1. Source addresses from 192.168.100.17 to 192.168.100.30, from the pool ip address named mypool .
Overload keyword allows you to map multiple IP addresses to a single registered IP address by using different ports. It can also be called Port Address Translation (PAT)
According to the question, the appropriate interface had been configured with NAT inside and NAT outside. But, below is how to configure NAT inside and NAT outside in case you’ve forgotten:
HQBR (config-if)#ip nat inside
HQBR (config)#interface s0/0
HQBR (config-if)#ip nat outside
Note: ensure you use the command below to copy your config;
HQBR #copy running-config startup-config (dont forget this bit)
Check your configuration for connectivity, click on “host for testing” and type:
If your configuration is correct, there will be reply from 192.0.2.114