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The access list must permit only those addresses that are to be translated. (Remember that there is an implicit "deny all" at
the end of each access list.) An access list that is too permissive can lead to unpredictable results.
See the "Overloading Inside Global Addresses Example" section at the end of this chapter for an
example of overloading inside global addresses.
6.3.9 Translating Overlapping Addresses
When an inside local address is identical with an outside address it wants to connect to, address
overlapping occurred.Figuer 6-3 shows how NAT translates overlapping networks.
The router performs the following process when translating overlapping addresses:
1. The user at host 1.1.1.1 opens a connection to host C by name, requesting a name-to-address
lookup from a DNS server.
2. DNS server responds and returns the address 1.1.1.1 of host C. The router intercepts the DNS reply
and selects an outside local address from outside local address pool to replace the source address.
Here the source address 1.1.1.1 will be replaced by 3.3.3.3.
3. The router sets up translations mapping inside local and global addresses to each other, and outside
global and local addresses to each other.
4. The destination address of messages host 1.1.1.1 sends to host C will be an outside local address
3.3.3.3.
5. When router A receives messages destined for outside local addresses, it will translate local address
into global address.
6. Host C receives the packet and continues the conversation.
6.3.10 Configuring Static Translation
To configure static source address translation, use the following commands in global configure
directory:
ip
nat
outside
global-ip local-ip
interface type number
ip nat inside
interface type number
ip nat outside
Command
source
static
Model Name
Figuer 6-3
Purpose
Establishes static translation between an outside local
address and an outside global address.
Specifies the inside interface.
Marks the interface as connected to the inside.
Specifies the outside interface.
Marks the interface as connected to the outside.
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