Home > Articles > Cisco Certification > CCNP > CCNP Self-Study: Advanced IP Addressing

CCNP Self-Study: Advanced IP Addressing

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Jun 11, 2004.

Solution to Configuration Exercise 1-2: NAT Using Access Lists and Route Maps

This section provides the answers to the questions in the Configuration Exercise.

NOTE

Some answers provided cover multiple steps; the answers are given after the last step for which that answer applies.

Solution to Task 1: Connecting the Internal Router to the Edge Router

Step 1

The internal routers (PxR3 and PxR4) should not have a configuration. If a configuration is present, use the erase start and reload commands to clear the configuration and reload the router.

Step 2

Connect to your internal routers. Supply an IP address to the Ethernet interface, and enable the interface. The Ethernet address of PxR3 should be 10.x.1.3/24, and the Ethernet address of PxR4 should be 10.x.2.4/24.


Solution:

The following example shows the configuration of P1R3:

The following example shows the configuration of P1R4:

 

Step 3

PxR1 has an Ethernet address of 10.x.1.1, and PxR2 has an Ethernet address of 10.x.2.2. Verify connectivity to the Ethernet-attached edge router from each internal router.


Solution:

To verify connectivity, the edge routers are pinged from the appropriate internal router.

The following output is from the P1R3 router. The ping was successful.

The following output is from the P1R4 router. The ping was successful.

Solution to Task 2: Setting Up ACL-Based NAT

NOTE

BBR1 has static routes for 192.168.x.0/24 and 192.168.xx.0/24. It does not have any remote routes for the pod 10.x.0.0 addresses, only its local TFTP server network 10.254.0.0.

Step 1

On the PxR1 and PxR2 routers, configure the sources to be translated using extended access list 100. Access list 100 should match traffic sourced from the network on your edge router's Ethernet interface, destined for the network that the TFTP server is located on. For example, PxR1 should match traffic sourced from 10.x.1.0/24, and PxR2 should match traffic sourced from 10.x.2.0/24. The access list must match only packets with a destination of 10.254.0.0/24.

Step 2

On the PxR1 and PxR2 routers, create a pool of addresses called BBR for use by NAT, using the ip nat pool command. PxR1 should use the address range of 192.168.x.0/24, and PxR2 should use 192.168.xx.0/24. For example, P2R1 would use 192.168.2.1 through 192.168.2.254, and P2R2 would use 192.168.22.1 through 192.168.22.254.

Step 3

On the PxR1 and PxR2 routers, use the ip nat inside source list command to specify that packets that match access list 100 should have their source addresses translated into the BBR pool.

Step 4

On the PxR1 and PxR2 routers, define which interfaces are inside or outside for NAT translation purposes.


Solution:

Because the traffic to be translated will come from the Ethernet interface, that will be the inside NAT interface. Translated traffic will leave via the Serial0 interface, so S0 will be the outside interface for NAT purposes. The following example shows the configuration on the P1R1 router:

  

Step 5

On the PxR3 and PxR4 routers, configure a default route pointing to the attached edge router e0 interface. This configuration allows the internal router to reach the core network.


Solution:

The following example shows the configuration on the P1R3 router:

 

Step 6

From the PxR3 and PxR4 routers, verify connectivity to the TFTP server (10.254.0.254) using the ping command.


Solution:

The following output shows the result of the ping command on the P1R3 router; the ping is successful.

CAUTION

You will not be able to reach the TFTP server if the NAT translation is not done correctly.

Step 7

View the NAT translation table on the edge router (PxR1 and PxR2).


Solution:

The following output shows the NAT translation table on the P1R1 router. From this output, you can see that one address has been translated.

Solution to Task 3: Translating to the Other Edge Router

Step 1

On the PxR1 and PxR2 routers, configure the source addresses to be translated using extended access list 101. Access list 101 should match traffic sourced from the network on your edge router's Ethernet interface, bound for any destination. For instance, PxR1 should match traffic from 10.x.1.0/24, and PxR2 should match traffic from 10.x.2.0/24. The access list must match packets with a destination to any network.

Step 2

On the PxR1 and PxR2 routers, create a pool of addresses named POD for use by NAT. PxR1 should use the address range 10.x.0.64 to 10.x.0.95, and PxR2 should use the address range 10.x.0.96 to 10.x.0.127.

Step 3

On the PxR1 and PxR2 routers, specify that packets that match access list 101 should have their source addresses translated into the POD pool.

Step 4

At the PxR1 and PxR2 routers, define the S1 interface of each router as the NAT outside interface by using the ip nat outside command so that traffic from the respective internal routers is translated.


Solution:

The following example shows the configuration of the P1R1 and P1R2 routers:

   

Step 5

From one internal router, ping the Serial 1 interface of the nonconnected edge router. (For example, from PxR3, ping the Serial 1 address of PxR2.) Is the ping successful?


Solution:

The following example is a ping from the P1R3 router to the P1R2 router's Serial 1 address:

The ping is unsuccessful.

Step 6

Look at the IP translation table on the edge routers to help explain the result of the previous ping.


Solution:

The following output is from the P1R1 router:

As you can see in the translation table, the P1R1 router has already translated the 10.1.1.3 source address, in Task 2, to 192.168.1.1. The router doesn't recognize that ping is a separate conversation, to a different destination, so it doesn't translate the traffic again for the new destination. You need a way to distinguish between different conversations.

Step 7

From the nonconnected edge router, use the debug ip icmp and debug ip packet commands while the pings are still active. Observe the output to help explain the results of the previous ping. Turn off all debugging when you are


finished.

Solution:

The following output is from the P1R2 router while the pings from P1R3 to the P1R2 Serial 1 address are ongoing:

P1R2 receives a packet with source address 192.168.1.1 and tries to reply to this packet. However, P1R2 reports that 192.168.1.1 is unroutable.

Step 8

Look at the routing table on the nonconnected edge router. Is there a route back to the destination address of the ping echo reply message?


Solution:

The following output is from the P1R2 router:

There is no route in P1R2's routing table to 192.168.1.1; this is why P1R2 cannot reply to the ping.

Step 9

What does a router do when it does not find an appropriate address?


Solution:

The router drops the packet.

Solution to Task 4: Using a Route Map with NAT to Translate Internal Addresses

Step 1

Create a route map that will be used to conditionally translate traffic based on the packet's destination.


Solution:

The following example shows the configuration on P1R1:

  

Step 2

Replace the translation commands from Task 3 with route map-based commands to perform the required translation.

 

If the router reports "%Dynamic mapping in use, cannot remove," simply go to privileged mode and enter the clear ip nat translation * command to remove all mappings. You then can configure the router.


Solution:

The following configuration is from the P1R1 router:

  

Step 3

Ping from one internal router to the opposite edge router and to the TFTP server to verify that the previous step was successful. Turn on debug ip nat detailed debugging on the edge routers to see the translation.


Solution:

The following ping output is from the P1R3 internal router to the TFTP server. (The P1R4 internal router produced the same result.)

The following debug output is from the P1R1 router while the preceding ping from P1R3 to the TFTP server was ongoing. This output shows the translation using the BBR pool:

The following ping output is from the P1R3 internal router to the P1R2 router's Serial 1 interface. (The same results were obtained when P1R4 pinged the P1R1 router Serial 1 interface.)

The following debug output is from the P1R1 router while the preceding ping from P1R3 to P1R2 was ongoing. This output shows the translation using the POD pool:

   

Step 4

Use the show ip nat translations command on each edge router to see the resulting NAT translation table.


Solution:

The following output is from the P1R1 and P1R2 routers:

Notice that the NAT translation table is completely developed. The inside and outside local and global addresses are included in the table, along with the TCP and UDP port numbers. Much more troubleshooting information is available within this table than with the table shown in Task 3.

Solution to Task 5: Downloading a Configuration File

On the internal routers, use TFTP to download the configuration file called PxRy.txt from the TFTP server to the running-config.

Solution:

The following configuration and output are from the P1R3 router. Notice that the router's name, P1R3, is configured after the configuration is downloaded:

The following configuration and output are from the P1R4 router. Again, notice that the router's name changes after the configuration is loaded:

NOTE

The configurations for PxR3 and PxR4 include the command no ip classless in preparation for the Configuration Exercise in the next chapter. If you try to communicate with the TFTP server now, it will not work. The reasoning behind this behavior is examined in the next Configuration Exercise.

Exercise Verification

You have successfully completed this exercise when you achieve the following results:

  • Your internal router can ping the TFTP server using a translation to 192.168.x.0/24.

  • Your internal router can ping the opposite edge router using a translation to 10.x.0.0/24.

  • You have demonstrated the limitations of access list-based NAT and have overcome those limitations by configuring NAT using a route map.

  • You have connected to the TFTP server through NAT and have downloaded a configuration file for your internal routers.

13. Review Questions | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020