Cisco CCNA Study Guide - Router Alley

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CCNA Study Guide v2.62 – Aaron Balchunas 302 NAT Terminology Example Consider the above example. For a connection from HostA to HostB, the NAT addresses are identified as follows: • Inside Local Address - 10.1.1.10 • Inside Global Address - 55.1.1.1 • Outside Global Address – 99.1.1.2 • Outside Local Address – 99.1.1.2 HostA’s configured address is 10.1.1.10, and is identified as its Inside Local address. When HostA communicates with the Internet, it is stamped with RouterA’s public address, using PAT. Thus, HostA’s Inside Global address will become 55.1.1.1. When HostA communicates with HostB, it will access HostB’s Outside Global address of 99.1.1.2. In this instance, the Outside Local address is also 99.1.1.2. HostA is never aware of HostB’s configured address. It is possible to map an address from the local network (such as 10.1.1.5) to the global address of the remote device (in this case, 99.1.1.2). This may be required if a legacy device exists that will only communicate with the local subnet. In this instance, the Outside Local address would be 10.1.1.5. Static NAT Translation 99.1.1.2 = 192.168.1.5 10.1.1.1 55.1.1.1 Internet 99.1.1.1 192.168.1.1 HostA 10.1.1.10 RouterA NAT-Enabled RouterA NAT-Enabled HostB 192.168.1.5 SRC Address = 10.1.1.10 DST Address = 99.1.1.2 SRC Address = 55.1.1.1:31092 DST Address = 99.1.1.2 SRC Address = 55.1.1.1:31092 DST Address = 192.168.1.5 The above example demonstrates how the source (SRC) and destination (DST) IP addresses within the Network-Layer header are translated by NAT. (Reference: http://www.cisco.com/warp/public/556/8.html) * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
CCNA Study Guide v2.62 – Aaron Balchunas 303 Configuring Static NAT The first step to configure Static NAT is to identify the inside (usually private) and outside (usually public) interfaces: Router(config)# int e0/0 Router(config-if)# ip nat inside Router(config)# int s0/0 Router(config-if)# ip nat outside To statically map a public address to a private address, the syntax is as follows: Router(config)# ip nat inside source static 172.16.1.1 158.80.1.40 This command performs a static translation of the source address 172.16.1.1 (located on the inside of the network), to the outside address of 158.80.1.40. Configuring Dynamic NAT When configuring Dynamic NAT, the inside and outside interfaces must first be identified: Router(config)# int e0/0 Router(config-if)# ip nat inside Router(config)# int s0/0 Router(config-if)# ip nat outside Next, a pool of global addresses must be specified. Inside hosts will dynamically choose the next available address in this pool, when communicating outside the local network: Router(config)# ip nat pool POOLNAME 158.80.1.1 158.80.1.50 netmask 255.255.255.0 The above command specifies that the pool named POOLNAME contains a range of public addresses from 158.80.1.1 through 158.80.1.50. Finally, a list of private addresses that are allowed to be dynamically translated must be specified: Router(config)# ip nat inside source list 10 pool POOLNAME Router(config)# access-list 10 permit 172.16.1.0 0.0.0.255 The first command states that any inside host with a source that matches access-list 10 can be translated to any address in the pool named POOLNAME. The access-list specifies any host on the 172.16.1.0 network. * * * All original material copyright © 2013 by Aaron Balchunas (aaron@routeralley.com), unless otherwise noted. All other material copyright © of their respective owners. This material may be copied and used freely, but may not be altered or sold without the expressed written consent of the owner of the above copyright. Updated material may be found at http://www.routeralley.com.
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Cisco CCNA Study Guide - Router Alley

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