User's Manual

402
Users Manual of CS-6306R
43.2.3.3 Translating Overlapping Addresses
When an internal local address is the same as the to-be-connected outside address, address overlapping
occurs. The following figure shows how NAT translates the overlapping addresses.
Figure 43-3 Network Condition Where NAT Translates Overlapping Addresses
The routing switch performs the following steps when translating the overlapping addresses:
(1) The user of host 1.1.1.1 uses domain name to send instructions for connecting host C. Host 1.1.1.1
requires DNS server to perform a checkup from domain name to address.
(2) The DNS server responds the request and returns the address 1.1.1.1 of host C. The routing switch
intercepts the DNS response message and selects an outside local address from the outside local
address pool to replace the source address. In this case, the source address 1.1.1.1 is replaced with
address 3.3.3.3.
(3) The routing switch creates a mapping table about address transfer, where inside local addresses and
inside global addresses map each other, outside global address and outside local address map each
other.
(4) Host 1.1.1.1 sends message to host C . The destination IP address is the outside local address 3.3.3.3.
(5) When switch A receives message whose destination address is the outside local address, switch A
transfers the local address to the global address.
(6) Host C receives the packet and continues the session.