CCNA RSE Lab: 9.3.1.5 TroubIeshootin NAT Confìurations
Topology
Addressing Table
Objectives
Part 1: Build the Network and Configure Basic Device Settings
Part 2: Troubleshoot Static NAT
Part 3: Troubleshoot Dynamic NAT
Background / Scenario
In this lab, the Gateway router was configured by an inexperienced network administrator at your company. Several errors in the configuration have resulted in NAT issues. Your boss has asked you to troubleshoot and correct the NAT errors and document your work. Ensure that the network supports the following:
- PC-A acts as a web server with a static NAT and will be reachable from the outside using the 209.165.200.254 address.
- PC-B acts as a host computer and dynamically receives an IP address from the created pool of addresses called NAT_POOL, which uses the 209.165.200.240/29 range.
Note: The routers used with CCNA hands-on labs are Cisco 1 941 Integrated Services Routers (ISRs) with Cisco IOS Release 1 5.2(4)M3 (universalk9 image). The switches used are Cisco Catalyst 2960s with Cisco IOS Release 1 5.0(2) (lanbasek9 image). Other routers, switches and Cisco IOS versions can be used. Depending on the model and Cisco IOS version, the commands available and output produced might vary from what is shown in the labs. Refer to the Router Interface Summary Table at the end of this lab for the correct interface identifiers.
Note: Make sure that the routers and switch have been erased and have no startup configurations. If you are unsure, contact your instructor.
Instructor Note: Refer to the Instructor Lab Manual for the procedures to initialize and reload devices.
Required Resources
- 2 Routers (Cisco 1941 with Cisco IOS Release 15.2(4)M3 universal image or comparable)
- 1 Switch (Cisco 2960 with Cisco IOS Release 15.0(2) lanbasek9 image or comparable)
- 2 PCs (Windows 7, Vista, or XP with terminal emulation program, such as Tera Term)
- Console cables to configure the Cisco IOS devices via the console ports
- Ethernet and serial cables as shown in the topology
Part 1: Build the Network and Configure Basic Device Settings
In Part 1, you will set up the network topology and configure the routers with basic settings. Additional NATrelated configurations are provided. The NAT configurations for the Gateway router contains errors that you will identify and correct as you proceed through the lab.
Step 1: Cable the network as shown in the topology.
Step 2: Configure PC hosts.
Step 3: Initialize and reload the switch and routers.
Step 4: Configure basic settings for each router.
a. Console into the router and enter global configuration mode.
b. Copy the following basic configuration and paste it to the running-configuration on the router.
no ip domain-lookup service password-encryption enable secret class banner motd # Unauthorized access is strictly prohibited. # line con 0 password cisco login logging synchronous line vty 0 4 password cisco login
c. Configure the host name as shown in the topology.
d. Copy the running configuration to the startup configuration.
Step 5: Configure static routing.
a. Create a static route from the ISP router to the Gateway router which was assigned public network address range 209.165.200.224/27.
ISP(config)# ip route 209.165.200.224 255.255.255.224 s0/0/0
b. Create a default route from the Gateway router to the ISP router.
Gateway(config)# ip route 0.0.0.0 0.0.0.0 s0/0/1
Step 6: Load router configurations.
The configurations for the routers are provided for you. There are errors with the configuration for the Gateway router. Identify and correct the configurations errors.
Gateway Router Configuration
interface g0/1 ip nat outside ! ip nat inside no shutdown interface s0/0/0 ip nat outside ! no ip nat outside interface s0/0/1 ! ip nat outside no shutdown ip nat inside source static 192.168.2.3 209.165.200.254 ! ip nat inside source static 192.168.1.3 209.165.200. 254 ip nat pool NAT_POOL 209.165.200.241 209.165.200.246 netmask 255.255.255.248 ip nat inside source list NAT_ACL pool NATPOOL ! ip nat inside source list NAT_ACL pool NAT_POOL ip access-list standard NAT_ACL permit 192.168.10.0 0.0.0.255 ! permit 192.168.1.0 0.0.0.255 banner motd $AUTHORIZED ACCESS ONLY$ end
Step 7: Save the running configuration to the startup configuration.
Part 2: Troubleshoot Static NAT
In Part 2, you will examine the static NAT for PC-A to determine if it is configured correctly. You will troubleshoot the scenario until the correct static NAT is verified.
a. To troubleshoot issues with NAT, use the debug ip nat command. Turn on NAT debugging to see translations in real-time across the Gateway router.
Gateway# debug ip nat
b. From PC-A, ping Lo0 on the ISP router. Do any NAT debug translations appear on the Gateway router?
No.
c. On the Gateway router, enter the command that allows you to see all current NAT translations on the Gateway router. Write the command in the space below. show ip nat translations
Gateway# show ip nat translations Pro Inside global Inside local Outside local Outside global --- 209.165.200. 254 192.168.2.3 --- ---
Why are you seeing a NAT translation in the table, but none occurred when PC-A pinged the ISP loopback interface? What is needed to correct the issue?
The static translation is for an incorrect inside local address.
d. Record any commands that are necessary to correct the static NAT configuration error.
Gateway(config)# no ip nat inside source static 192.168.2.3 209.165.200. 254 Gateway(config)# ip nat inside source static 192.168.1.3 209.165.200. 254
e. From PC-A, ping Lo0 on the ISP router. Do any NAT debug translations appear on the Gateway router?
No
f. On the Gateway router, enter the command that allows you to observe the total number of current NATs.
Write the command in the space below. show ip nat statistics
Gateway# show ip nat statistics Total active translations: 1 (1 static, 0 dynamic; 0 extended) Peak translations: 1, occurred 00:08:12 ago Outside interfaces: GigabitEthernet0/1, Serial0/0/0 Inside interfaces: Hits: 0 Misses: 0 CEF Translated packets: 0, CEF Punted packets: 0 Expired translations: 0 Dynamic mappings: -- Inside Source [Id: 1] access-list NAT_ACL pool NATPOOL refcount 0 Total doors: 0 Appl doors: 0 Normal doors: 0 Queued Packets: 0
Is the static NAT occurring successfully? Why?
No NAT translation is occurring because both of G0/1 and S0/0/0 interfaces are configured with the ip nat outside command. No active interfaces area assigned as inside.
g. On the Gateway router, enter the command that allows you to view the current configuration of the router. Write the command in the space below.
show running-config Gateway# show running-config Building configuration... Current configuration : 1806 bytes ! version 15.2 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname Gateway ! boot-start-marker boot-end-marker ! enable secret 4 06YFDUHH61wAE/kLkDq9BGho1QM5EnRtoyr8cHAUg.2 ! no aaa new-model ! no ip domain lookup ip cef no ipv6 cef ! multilink bundle-name authenticated ! redundancy ! interface GigabitEthernet0/0 no ip address shutdown duplex auto speed auto ! interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 ip nat outside ip virtual-reassembly in duplex auto speed auto ! interface Serial0/0/0 no ip address ip nat outside ip virtual-reassembly in shutdown clock rate 2000000 ! interface Serial0/0/1 ip address 209.165.200.225 255.255.255.252 ! ip forward-protocol nd ! no ip http server no ip http secure-server ! ip nat pool NAT_POOL 209.165.200.241 209.165.200.246 netmask 255.255.255.248 ip nat inside source list NAT_ACL pool NATPOOL ip nat inside source static 192.168.1.3 209.165.200. 254 ip route 0.0.0.0 0.0.0.0 Serial0/0/1 ! ip access-list standard NAT_ACL permit 192.168.10.0 0.0.0.255 ! control-plane ! banner motd ^CAUTHORIZED ACCESS ONLY^C ! line con 0 password cisco logging synchronous login line aux 0 line 2 no activation-character no exec transport preferred none transport input all transport output pad telnet rlogin lapb-ta mop udptn v120 ssh stopbits 1 line vty 0 4 password cisco login transport input all ! scheduler allocate 20000 1000 ! end
h. Are there any problems with the current configuration that prevent the static NAT from occurring?
Yes. The inside and outside NAT interfaces are incorrectly configured.
i. Record any commands that are necessary to correct the static NAT configuration errors.
Gateway(config)# interface g0/1 Gateway(config-if)# no ip nat outside Gateway(config-if)# ip nat inside Gateway(config-if)# exit Gateway(config)# interface s0/0/0 Gateway(config-if)# no ip nat outside Gateway(config-if)# exit Gateway(config)# interface s0/0/1 Gateway(config-if)# ip nat outside Gateway(config-if)# exit
j. From PC-A, ping Lo0 on the ISP router. Do any NAT debug translations appear on the Gateway router?
Yes
*Mar 18 23:53:50.707: NAT*: s=192.168.1.3->209.165.200.254, d=198.133.219.1 [187] *Mar 18 23:53:50.715: NAT*: s=198.133.219.1, d=209.165.200.254->192.168.1.3 [187] Gateway# *Mar 18 23:53:51.711: NAT*: s=192.168.1.3->209.165.200.254, d=198.133.219.1 [188] *Mar 18 23:53:51.719: NAT*: s=198.133.219.1, d=209.165.200.254->192.168.1.3 [188] *Mar 18 23:53:52.707: NAT*: s=192.168.1.3->209.165.200.254, d=198.133.219.1 [189] Gateway# *Mar 18 23:53:52.715: NAT*: s=198.133.219.1, d=209.165.200.254->192.168.1.3 [189] *Mar 18 23:53:53.707: NAT*: s=192.168.1.3->209.165.200.254, d=198.133.219.1 [190] Gateway# *Mar 18 23:53:53.715: NAT*: s=198.133.219.1, d=209.165.200.254->192.168.1.3 [190]
k. Use the show ip nat translations verbose command to verify static NAT functionality.
Note: The timeout value for ICMP is very short. If you do not see all the translations in the output, redo the ping.
Gateway# show ip nat translations verbose Pro Inside global Inside local Outside local Outside global icmp 209.165.200. 254:1 192.168.1.3:1 198.133.219.1:1 198.133.219.1:1 create 00:00:04, use 00:00:01 timeout:60000, left 00:00:58, flags: extended, use_count: 0, entry-id: 12, lc_entries: 0 --- 209.165.200. 254 192.168.1.3 --- --- create 00:30:09, use 00:00:04 timeout:0, flags: static, use_count: 1, entry-id: 2, lc_entries: 0
Is the static NAT translation occurring successfully? ____________________ Yes
If static NAT is not occurring, repeat the steps above to troubleshoot the configuration.
Part 3: Troubleshoot Dynamic NAT
a. From PC-B, ping Lo0 on the ISP router. Do any NAT debug translations appear on the Gateway router?
No
b. On the Gateway router, enter the command that allows you to view the current configuration of the router.
Are there any problems with the current configuration that prevent dynamic NAT from occurring?
Yes. The NAT pool is incorrectly identified in the source statement. The NAT access list has an incorrect network statement.
c. Record any commands that are necessary to correct the dynamic NAT configuration errors.
Gateway(config)# no ip nat inside source list NAT_ACL pool NATPOOL Gateway(config)# ip nat inside source list NAT_ACL pool NAT_POOL Gateway(config)# ip access-list standard NAT_ACL Gateway(config-std-nacl)# no permit 192.168.10.0 0.0.0.255 Gateway(config-std-nacl)# permit 192.168.1.0 0.0.0.255
d. From PC-B, ping Lo0 on the ISP router. Do any NAT debug translations appear on the Gateway router?
Yes
*Mar 19 00:01:17.303: NAT*: s=192.168.1.4->209.165.200.241, d=198.133.219.1 [198] *Mar 19 00:01:17.315: NAT*: s=198.133.219.1, d=209.165.200.241->192.168.1.4 [198] Gateway# *Mar 19 00:01:18.307: NAT*: s=192.168.1.4->209.165.200.241, d=198.133.219.1 [199] *Mar 19 00:01:18.315: NAT*: s=198.133.219.1, d=209.165.200.241->192.168.1.4 [199] *Mar 19 00:01:19.303: NAT*: s=192.168.1.4->209.165.200.241, d=198.133.219.1 [200] Gateway# *Mar 19 00:01:19.315: NAT*: s=198.133.219.1, d=209.165.200.241->192.168.1.4 [200] *Mar 19 00:01:20.303: NAT*: s=192.168.1.4->209.165.200.241, d=198.133.219.1 [201] *Mar 19 00:01:20.311: NAT*: s=198.133.219.1, d=209.165.200.241->192.168.1.4 [201]
e. Use the show ip nat statistics to view NAT usage.
Gateway# show ip nat statistics Total active translations: 2 (1 static, 1 dynamic; 0 extended) Peak translations: 3, occurred 00:02:58 ago Outside interfaces: Serial0/0/1 Inside interfaces: GigabitEthernet0/1 Hits: 24 Misses: 0 CEF Translated packets: 24, CEF Punted packets: 0 Expired translations: 3 Dynamic mappings: -- Inside Source [Id: 2] access-list NAT_ACL pool NAT_POOL refcount 1 pool NAT_POOL: netmask 255.255.255.248 start 209.165.200.241 end 209.165.200.246 type generic, total addresses 6, allocated 1 (16%), misses 0 Total doors: 0 Appl doors: 0 Normal doors: 0 Queued Packets: 0
Is the NAT occurring successfully? _______________ Yes
What percentage of dynamic addresses has been allocated? __________ 16%
f. Turn off all debugging using the undebug all command.
Reflection
1. What is the benefit of a static NAT?
A static NAT translation allows users from outside the LAN to access a computer or server on the internal network.
2. What issues would arise if 10 host computers in this network were attempting simultaneous Internet communication?
Not enough public addresses exist in the NAT pool to satisfy 10 simultaneous user sessions. As hosts drop off, different hosts will be able to claim the pool addresses to access the Internet
Router Interface Summary Table
Router Interface Summary |
||||
Router Model | Ethernet Interface #1 | Ethernet Interface #2 | Serial Interface #1 | Serial Interface #2 |
1800 | Fast Ethernet 0/0 (F0/0) |
Fast Ethernet 0/1 (F0/1) |
Serial 0/0/0 (S0/0/0) | Serial 0/0/1 (S0/0/1) |
1900 | Gigabit Ethernet 0/0 (G0/0) |
Gigabit Ethernet 0/1 (G0/1) |
Serial 0/0/0 (S0/0/0) | Serial 0/0/1 (S0/0/1) |
2801 | Fast Ethernet 0/0 (F0/0) |
Fast Ethernet 0/1 (F0/1) |
Serial 0/1 /0 (S0/1 /0) | Serial 0/1 /1 (S0/1 /1) |
2811 | Fast Ethernet 0/0 (F0/0) |
Fast Ethernet 0/1 (F0/1) |
Serial 0/0/0 (S0/0/0) | Serial 0/0/1 (S0/0/1) |
2900 | Gigabit Ethernet 0/0 (G0/0) | Gigabit Ethernet 0/1 (G0/1) | Serial 0/0/0(S0/0/0) | Serial 0/0/1 (S0/0/1) |
Note: To find out how the router is configured, look at the interfaces to identify the type of router and how many interfaces the router has. There is no way to effectively list all the combinations of configurations for each router class. This table includes identifiers for the possible combinations of Ethernet and Serial interfaces in the device. The table does not include any other type of interface, even though a specific router may contain one. An example of this might be an ISDN BRI interface. The string in parenthesis is the legal abbreviation that can be used in Cisco IOS commands to represent the interface. |
Device Config
Router Gateway
Gateway#show run Building configuration... Current configuration : 1805 bytes ! version 15.2 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname Gateway ! boot-start-marker boot-end-marker ! enable secret 4 06YFDUHH61wAE/kLkDq9BGho1QM5EnRtoyr8cHAUg.2 ! no aaa new-model ! no ip domain lookup ip cef no ipv6 cef ! multilink bundle-name authenticated ! redundancy ! interface Embedded-Service-Engine0/0 no ip address shutdown ! interface GigabitEthernet0/0 no ip address shutdown duplex auto speed auto ! interface GigabitEthernet0/1 ip address 192.168.1.1 255.255.255.0 ip nat inside ip virtual-reassembly in duplex auto speed auto ! interface Serial0/0/0 no ip address shutdown ! interface Serial0/0/1 ip address 209.165.200.225 255.255.255.252 ip nat outside ip virtual-reassembly in ! ip forward-protocol nd ! no ip http server no ip http secure-server ! ip nat pool NAT_POOL 209.165.200.241 209.165.200.246 netmask 255.255.255.248 ip nat inside source list NAT_ACL pool NAT_POOL ip nat inside source static 192.168.1.3 209.165.200.254 ip route 0.0.0.0 0.0.0.0 Serial0/0/1 ! ip access-list standard NAT_ACL permit 192.168.1.0 0.0.0.255 ! control-plane ! banner motd ^CAUTHORIZED ACCESS ONLY^C ! line con 0 password cisco logging synchronous login line aux 0 line 2 no activation-character no exec transport preferred none transport input all transport output pad telnet rlogin lapb-ta mop udptn v120 ssh stopbits 1 line vty 0 4 password cisco login transport input all ! scheduler allocate 20000 1000 !e nd
Router ISP
ISP#show run Building configuration... Current configuration : 1482 bytes ! version 15.2 service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname ISP ! boot-start-marker boot-end-marker ! enable secret 4 06YFDUHH61wAE/kLkDq9BGho1QM5EnRtoyr8cHAUg.2 ! no aaa new-model memory-size iomem 15 ! no ip domain lookup ip cef ! no ipv6 cef multilink bundle-name authenticated ! interface Loopback0 ip address 198.133.219.1 255.255.255. 255 ! interface Embedded-Service-Engine0/0 no ip address shutdown ! interface GigabitEthernet0/0 no ip address shutdown duplex auto speed auto ! interface GigabitEthernet0/1 no ip address shutdown duplex auto speed auto ! interface Serial0/0/0 ip address 209.165.200.226 255.255.255.252 clock rate 128000 ! interface Serial0/0/1 no ip address shutdown ! ip forward-protocol nd ! no ip http server no ip http secure-server ! ip route 209.165.200.224 255.255.255.224 Serial0/0/0 ! control-plane ! line con 0 password cisco logging synchronous login line aux 0 line 2 no activation-character no exec transport preferred none transport input all transport output pad telnet rlogin lapb-ta mop udptn v120 ssh stopbits 1 line vty 0 4 password cisco login transport input all line vty 5 15 password cisco login transport input all ! scheduler allocate 20000 1000 ! end
More Resources