ZyXEL Communications P-2812HNU-51c User Manual page 114

Chapter 5 WAN Setup
router also maps packets coming to that external IP address and port to the
internal IP address and port.
In the following example, the P-2812HNU-51c maps the source address of all
packets sent from the internal IP address 1 and port A to IP address 2 and port B
on the external network. The P-2812HNU-51c 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 46 Full Cone NAT Example
1, A
2, B
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 P-2812HNU-51c 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 P-2812HNU-51c 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-2812HNU-51c User's Guide