1.1.1 opens a connection to host B. The ?¬?rst packet
that the router receives from host 10.1.1.1 causes the router to check its
NAT table.
Step 2 If no translation entry exists, the router determines that address 10.1.1.1
must be translated and sets up a translation of inside local address
10.1.1.1 into a legal inside global address. If overloading is enabled and
another translation is active, the router reuses the inside global address
from that translation and saves enough information to be able to translate
back. This type of entry is called an extended entry.
Step 3 The router replaces the inside local source address 10.1.1.1 with the
selected inside global address and forwards the packet.
Step 4 Host B receives the packet and responds to host 10.1.1.1 by using the
inside global IP address 171.69.68.2.
Step 5 When the router receives the packet with the inside global IP address, the
router performs a NAT table lookup. Using the inside global address and
port and outside global address and port as a key, the router translates the
address back into the inside local address 10.1.1.1 and forwards the
packet to host 10.1.1.1. Host 10.1.1.1 receives the packet and continues
the conversation. The router performs Steps 2 through 5 for each packet.
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