User's Manual

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Users Manual of CS-6306R
Refer to section 2.4.1 “Dynamic Inside Source Address Transfer Example” for
details.
43.2.3.2 Reloading Inside Global Address
Multiple local addresses use one global address through the routing switch. All the addresses can be stored in
the inside global address pool. When the reloading is configured, the routing switch maintains sufficient
information from high-level protocols (such as TCP or UDP) and transfers the global address to the correct
local address. When multiple local addresses are mapped to one global address, TCP or UDP port numbers
of each inside host are used to label multiple local addresses.
The following figure shows the NAT operation when an inside global address represents multiple local
addresses. TCP port number is used to label the local address.
Figure 43-2 NAT Operation During the Reloading of Inside Global Address
The routing switch performs the following steps in the reloaded inside global address. Host B and host C think
that they are communicating with host 2.2.2.2. However, they are communicating with different hosts in fact.
The port number is the identifier. In fact, multiple inside hosts can share one inside global IP address using
different port numbers.
(1) The user of host 1.1.1.1 creates a connection between host 1.1.1.1 and host B.
(2) The routing switch receives the first message from host 1.1.1.1 and then checks its NAT table.
If no transfer items exist, the switch decides that address 1.1.1.1 must be translated, and then creates a
translation between inside local address 1.1.1.1 and legal global address. If the reloading is successful,
another translation is started up. The switch reuses the global address in the previous translation and saves
sufficient transferable information. The item is called as the expansion item.
(3) The routing switch replaces the inside local source address 1.1.1.1 with the selected global address,
and then forwards a packet.
(4) Host B receives the packet and responds to host 1.1.1.1 using inside global IP address 2.2.2.2.
(5) When the routing switch receives the packet with the inside global IP address, it uses the protocol,
inside global address, outside address and port as the keywords to search the NAT table. After that, it
transfers the address to the inside local address 1.1.1.1 and forwards the packet to host 1.1.1.1.
(6) Host 1.1.1.1 receives the packet and continues the session. The routing switch performs step 2 and step
5 for each packet.