ZyXEL Communications P-870HN-5xb User Manual page 99

Chapter 5 WAN Setup
external network. The Device also performs NAT on all incoming packets sent to IP
address 2 and port B and forwards them to IP address 1, port A.
Figure 45 Full Cone NAT Example
2, B
1, A
Symmetric NAT
The full, restricted and port restricted cone NAT types use the same mapping for
an outgoing packet's source address regardless of the destination IP address and
port. In symmetric NAT, the mapping of an outgoing packet's source address to a
source address in another network is different for each different destination IP
address and port.
In the following example, the Device maps the source address IP address 1 and
port A to IP address 2 and port B on the external network for packets sent to IP
address 3 and port C. The Device uses a different mapping (IP address 2 and port
M) for packets sent to IP address 4 and port .
D
A host on the external network (IP address 3 and port C for example) can only
send packets to the internal host via the external IP address and port that the NAT
router used in sending a packet to the external host's IP address and port. So in
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P-870HN-5xb User's Guide