User's Manual

Configuring GRE, NAT, RIPSO, and BFE Services
2-54
308625-14.00 Rev 00
The following events occur:
1. NAT receives a packet from host A on the local interface with a local source
address of 55.0.0.1 and a port number of 2001.
2. Determining that the local source address falls within the range configured for
N-to-1 translation, NAT stores the port number, replaces the local source
address with the global address, 192.1.1.1, replaces the local port number with
the unique port number 12000, and transmits the packet on the global
interface.
3. Subsequently, NAT receives a packet from host B on the local interface with
local source address 55.0.0.2 and port number 2222. Determining that this
local source address falls in the same configured range, NAT replaces the
local source address with the global address, 192.1.1.1, replaces the local port
number with the unique port number 54000, and transmits the packet on the
global interface.
When NAT receives a packet from a remote source on the global interface, the
following events occur:
1. NAT determines that the destination address on the packet is an N-to-1
address.
2. NAT uses the address and the port number to identify the destination host.
3. NAT replaces the destination IP address and TCP port number with the
original local address and port number and transmits it on the local interface.
In Figure 2-7
, for example, the following events occur:
1. NAT receives a packet on the global interface with the destination address
192.1.1.1 and port number 12000.
2. Determining that the destination address is an N-to-1 address, NAT uses the
address and the port number to locate the destination host, host A. NAT
replaces the global destination address and TCP port number with the local
address and port number and transmits the packet on the local interface.