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CCNA(640-802) Lab – NAT(New)


NAT is Short for Network Address Translation, an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP address translations.

NAT serves three main purposes:

  • Provides a type of firewall by hiding internal IP addresses
  • Enables a company to use more internal IP addresses. Since they're used internally only, there's no possibility of conflict with IP addresses used by other companies and organizations.
  • Allows a company to combine multiple ISDN connections into a single Internet connection.
  • I suggest you should study NAT knowledge carefully, and then start following lab.

    802-1NAT SIM Configuration:
    The following configuration translates between inside hosts addressed from 192.168.16.33 /28 network (192.168.16.33 – 192.168.16.46) to the globally unique pool of address provided by ISP 198.18.237.225 – 198.18.237.230 /29.
    P4S-R>enable
    P4S-R#configure terminal
    Before starting the NAT configuration verify that router hostname currently configured is P4S-R. If not change hostname to P4S-R using the command
    Router(config)#hostname P4S-R

    Step1: Create an access-list to match all the P4S-R LAN address that need to be the candidates for NAT translations
    P4S-R(config)#access-list 10 permit 192.168.16.32 0.0.0.15

    Step2: Create a NAT Pool with pool name isp_p4s and specify the pool address range provided by ISP with their netmask.
    P4S-R(config)#ip nat pool isp_p4s 198.18.237.225 198.18.237.230 netmask 255.255.255.248

    Step3: Packets that match access-list 10 will be translated to an address from the pool called "isp_p4s".
    Overload keyword specify to use Port based NATing to support all the P4S-R LAN address range.
    P4S-R(config)#ip nat inside source list 10 pool isp_p4s overload
    SIM Question already provides that appropriate interfaces have been configured for NAT Inside and NAT Outside statements.
    For your information configuration would have been like this:
    P4S-R(config)#interface fastethernet 0/0
    P4S-R(config-if)#ip nat inside
    P4S-R(config-if)#no shutdown


    P4S-R(config)#interface serial 0/0
    P4S-R(config-if)#ip nat outside
    P4S-R(config-if)#no shutdown
    Functionality Test:

    Our requirements are to allow the hosts (P4S-R LAN) the ability to communicate with the Internet. For this test, we ping the Internet device (ISP router S0/1) from Host for testing.
    Step4:
    Go to host for testing:
    C:>ping 192.0.2.114

    PING should be success to 192.0.2.114 since SIM question provides that static route is already configured on router.
    Step5:
    On console of router (P4S-R) :
    Issue show ip nat translation command to verify the NAT translations.
    Sample output:
    Considering host for testing IP address is 192.168.16.33
    P4S-R# show ip nat translation

    Pro Inside global Inside local Outside local Outside global
    icmp 198.18.237.225:434 192.168.16.33:434 192.0.2.113:434 192.0.2.114:434
    icmp 198.18.237.225:435 192.168.16.33:435 192.0.2.113:435 192.0.2.114:435
    icmp 198.18.237.225:436 192.168.16.33:436 192.0.2.113:436 192.0.2.114:436
    icmp 198.18.237.225:437 192.168.16.33:437 192.0.2.113:437 192.0.2.114:437
    icmp 198.18.237.225:438 192.168.16.33:438 192.0.2.113:438 192.0.2.114:438

    Step 6:
    Important please do not forget to save your running-config to startup-config
    P4S-R2# copy run start

    That is all, hope to helpful for you. Best Luck for ur CCNA 640-802 Exam.

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    Post date: 2009-04-03 17:43:23
    Post date GMT: 2009-04-03 09:43:23
    Post modified date: 2009-04-03 17:46:03
    Post modified date GMT: 2009-04-03 09:46:03
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