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- Static NAT performs one-to-one mapping between inside local and inside global addresses.
Figure 17-3 shows a typical static NAT scenario. An organization that has 254 private hosts
would need a single registered Class C IP subnet (/24 – 254 usable IP addresses) to provide
Internet access to all its hosts, which is definitely a waste of public IP addresses!
Inside
Figure 17-3: Static NAT
- Dynamic NAT performs dynamic mapping between an inside local and inside global addresses
from a pool of public IP addresses. An available registered IP address from the NAT pool will be
allocated to a private host when it communicates with a host on the Internet. The major limitation
of dynamic NAT is it can only provide Internet access to a very limited number of private hosts
(the number of registered IP addresses of the NAT pool).
Inside
172.16.1.1
172.16.1.2
172.16.1.1
172.16.1.2
Before
After
NAT
Inside Local Inside Global
Inside Local Inside Global
172.16.1.1
172.16.1.2
172.16.1.3
NAT
Inside Local Inside Global
172.16.1.1
172.16.1.2
NAT Table
150.1.1.1
150.1.1.2
NAT Table
150.1.1.1
150.1.1.2
–
Figure 17-4: Dynamic NAT
126
Internet
Internet
200.1.1.1
200.1.1.1
NAT Pool
150.1.1.1
150.1.1.2
Outside
Outside
Copyright © 2008 Yap Chin Hoong
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