Answers Note: Red font color or gray highlights indicate text that appears in the instructor copy only.

Addressing Table

The following table provides addressing for networking device interfaces only.

Objectives

Part 1: Investigate NAT Operation Across the Intranet

Part 2: Investigate NAT Operation Across the Internet

Part 3: Conduct Further Investigations

Scenario

As a frame travels across a network, the MAC addresses may change. IP addresses can also change when a packet is forwarded by a device configured with NAT. In this activity, we will investigate what happens to IP addresses during the NAT process.

Instructions

Part 1:  Investigate NAT Operation Across the Intranet

Step 1:  Wait for the network to converge.

It might take a few minutes for everything in the network to converge. You can speed the process up by clicking Fast Forward Time.

Step 2:  Generate an HTTP request from any PC in the Central domain.

1. Switch to Simulation mode and edit the filters to show only HTTP requests.
2. Open the Web Browser of any PC in the Central domain and type the URL http://branchserver.pka and click Go. Minimize the browser window.
3. Click Capture / Forward until the PDU is over D1 or D2. Click on the most recent PDU in the Event List. Record the source and destination IP addresses.

Question:

To what devices do those addresses belong?

Type your answers here.

10.X.X.X and 64.100.200.1 The PC and R4.

4. Click Capture / Forward until the PDU is over R2. Record the source and destination IP addresses in the outbound packet.

Question:

To what devices do those addresses belong?

Type your answers here.

64.100.100.X and 64.100.200.1 The first address is not assigned to an interface. R4 is the second address.

5. Login to R2 from the CLI using the password class to enter privileged EXEC and issue the following command:

Open configuration window

R2# show run | include pool

ip nat pool R2Pool 64.100.100.3 64.100.100.31 netmask 255.255.255.224

ip nat inside source list 1 pool R2Pool

The address came from the NAT pool R2Pool.

6. Click Capture / Forward until the PDU is over R4. Record the source and destination IP addresses in the outbound packet.

Question:

To what devices do those addresses belong?

Type your answers here.

64.100.100.X and 172.16.0.3. The first address is from R2Pool on R2. Branchserver.pka is the second address.

7. Click Capture / Forward until the PDU is over Branchserver.pka. Record the source and destination TCP port addresses in the outbound segment.

Type your answers here.

source 80, destination 102x

8. On both R2 and R4, run the following command and match the IP addresses and ports recorded above to the correct line of output:

R2# show ip nat translations

R4# show ip nat translations

Questions:

What do the inside local IP addresses have in common?

Type your answers here.

They are reserved for private use.

Did any private addresses cross the intranet?

Type your answers here.

No.

Close configuration window

9. Click the Reset Simulation button and remain in Simulation Model.

Part 2:  Investigate NAT Operation Across the Internet

Step 1:  Generate an HTTP request from any computer in the home office.

1. Open the Web Browser of any PC in the Home Office domain and type the URL http://centralserver.pka and click Go.
2. Click Capture / Forward until the PDU is over WRS. Record the inbound source and destination IP addresses and the outbound source and destination addresses.

Question:

To what devices do those addresses belong?

Type your answers here.

Inbound: 192.168.0.X and 64.100.100.2. Outbound: 64.104.223.2 and 64.100.100.2. The computer and R2; WRS and R2.

3. Click Capture / Forward until the PDU is over R2. Record the source and destination IP addresses in the outbound packet.

Question:

To what devices do those addresses belong?

Type your answers here.

64.104.223.2 and 10.10.10.2, which is WRS and centralserver.pka.

4. On R2, run the following command and match the IP addresses and ports recorded above to the correct line of output:

Open configuration window

R2# show ip nat translations

Close configuration window

5. Return to Realtime mode.

Question:

Did all of the web pages appear in the browsers?

Type your answers here.

Yes.

Part 3:  Conduct Further Investigations

Experiment with more packets, both HTTP and HTTPS and answer the following questions.

Questions:

Do the NAT translation tables grow?

Type your answers here.

Yes. There are additional entries as new conversations are started.

Does WRS have a NAT pool of addresses?

Type your answers here.

No, it uses the same IP address for all devices.

Is this how the computers in the classroom connect to the internet?

Type your answers here.

It depends on the campus infrastructure. An easy way to check is using something like https://www.whatsmyip.org to determine if all machines in the classroom are using the same address.

Why does NAT use four columns of addresses and ports?

Type your answers here.

The columns list the inside global, inside local, outside local, and outside global addresses.

Where are the networks are inside global and inside local?

Type your answers here.

The inside local addresses are on the LANs within each domain. The outside global addresses are from the WAN links to the internet and intranet.

On which devices are NAT services operating? What do they have in common?

Type your answers here.

WRS, R2, and R4. They all connect internal LANs to outside networks that require routable IP addresses.