Intel ER8100STUS - Express 8100 Router Reference Manual page 73

Communications
between internal and
external addresses
using Dynamic Mapping
up to 256 addresses. In this case, the entire internal address (network and host
part) must be translated to an assigned external address. External addresses are
therefore assigned sequentially as they are required.
When using Dynamic Mapping, only internal networks can initiate
Note
communications with external devices. External devices do not know
the address of the internal device until it has been informed of it by a
packet from the device. For this reason, static links must be established
to internal network devices which you wish to make accessible to the
external network.
The above diagram gives an example using Dynamic Mapping between an inter-
nal class B network (address 10.2.0.0) and an external class C network address
(address 177.4.5.0). The full IP address is translated and the internal host ad-
dresses are assigned external IP addresses sequentially when they initiate com-
munications over the IP link.
When using Dynamic Mapping, only internal devices can initiate communica-
tions with external devices. Internal addresses are unknown to the external net-
work and a translation address is assigned dynamically whenever an internal
device initiates communications with an external device. Following the initial
communication, external addresses can then communicate with the translated ad-
dress for as long as it remains in the NAT table. Internal addresses remain in the
NAT table for at least 1 hour following the last communication—that is, the timer
IP Routing
IP Concept
61