Lab 11.3.3: Configuring Overloading NAT with Frame Relay

Objectives:

  • To configure a Frame Relay connection between our Company router in Orlando and the ISP's router in Houston, and configure overloading Network Address Translation on the Company router.

Scenario:

Our quickly growing company has the network number 206.222.222.0, which was assigned by ARIN. Previously the company was using dynamic address translation over an ISDN line however the company has just upgraded the line to Frame Relay. The company has been growing and has outgrown the number of valid IP addresses. The company is not able to get another class C network from ARIN, so we need to find another solution which will allow all of our employees Internet access without over running the available valid IP addresses. We have researched NAT and found that if set up properly we can translate many internal IP addresses into one valid IP address. This is called Overloading Network Address Translation. It is our job to configure the Frame Relay connection and implement the proper address translation.

Notes: 

Lab Tasks:

  1. Cable the lab as shown in the diagram.
  2. The next task is to set up the routers and ISDN connection as in previous labs:

    • Configure IGRP routing with the AS# 808.
    • Configure the correct IP addresses on each of the routers.
    • Configure the encapsulation type, DLCI, LMI type, and any frame relay maps.

    Don't forget the no shutdown command on the interfaces.

  3. Before configuring overloading address translation on the routers, test your configurations by pinging the other router. This way you are insuring that your basic configuration is correct before changing it.
  4. The first step in configuring Overloading network address translation is to define a pool of global addresses (real IP addresses) to be allocated as needed:

    Company(config)#ip nat pool net-206 206.222.222.1 206.222.222.2 netmask 255.255.255.0
  5. Next we need to define a standard access list.

    Company(config)#access-list 3 permit 10.30.0.0 0.0.255.255

    Based on the previous Network Address Translation labs, what is the purpose of this
    access list?

  6. Now is the time to enter the command to establish dynamic source translation, identifying the access list defined in the previous step. However, we are going to add one word to the command to get it to understand that it should translate multiple internal IP addresses (local addresses) into just one real IP address (global address).

    Company(config)#ip nat inside source list 3 pool net-206 overload

    Explain in your own words what the previous command is telling the router.

  7. We next need to tell the router which interface is connected to inside network and which interface is connected to the outside.

    Company(config)#interface fast ethernet 0/0
    Company(config-if)#ip nat inside

    Company(config)#interface serial 0/0
    Company(config-if)#ip nat outside

    Why is it important for the router to know which interface is connected to the inside network and which is connected to the outside network?

  8. Now we get to verify the routers address translation.

    Company#show ip nat translations

    What information did the router respond with?

    Company#show ip nat translations verbose

    What additional information did the router respond with?

    Company#show ip nat statistics

    What information did the router respond with?

  9. Hope you didn't forget to add the static route on the ISP router. Now it is time to test our new configuration. From a workstation on the inside network attached to the Company router, ping an address on the outside network (the workstation on the ISP's network).

    Company#show ip nat translations

    What information did the router respond with?

    Company#show ip nat statistics

    What information did the router respond with?

  10. From the ISP router ping an address which has a nat listing on the translation table.

    Were you successful?

  11. Now ping an address that is not currently in the routers translation table.

Were you successful?

Explain the results of the previous two questions.

What is meant by NAT "overloading"?

Is it possible to be able to configure both static NAT and overloading NAT on the same router at the same time? If so, explain how.