User's Manual

Configuring GRE, NAT, RIPSO, and BFE Services
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The destination host uses the incoming packet’s source address to create a
destination address to send a packet back to the sending host. When the packet
arrives at company A’s NAT router:
1.
The NAT router checks the packet’s destination address. If it is a global
address from a configured global address range, NAT compares the
destination address to entries in its translation table.
2.
If the NAT router finds the packet’s original IP address in the translation table,
it replaces the destination address with its original local address.
After a specified timeout period during which there have been no translated
packets for a particular address translation, company A’s NAT router removes the
mapping, freeing the global address for use by another inside host.
NAT Address Translation Options
You can configure three types of network address translation:
• Dynamic address translation
• Static address translation
• Network address port translation (N-to-1)
Dynamic Address Translation
Dynamic address translation creates a temporary mapping of an unregistered
address to a global address. The NAT router selects a global address from one or
more global address pools that you configure, and maps this address to the
unregistered address. The translation remains in a translation table for as long as it
is active. An idle entry is removed after a specified timeout period (see
“Configuring the Translation Entry Timeout Value
” on page 2-29). If the timeout
parameter is disabled, the mapping is not removed.
For instructions on how to create and enable dynamic address translation, see the
following sections: “Configuring Dynamic Local Address Ranges
” on page 2-43
and “Configuring Dynamic Global Address Ranges
” on page 2-48.