Introduction
131
IPLink Software Configuration Guide
12 • NAT/NAPT configuration
Dynamic NAT
NAT only modifies addresses but not ports. Dynamic NAT assigns a global address from a global NAT address
pool each time a local host wants to access the global network. It creates a dynamic NAT entry for the reverse
path. If a connection is idle for some time (2 minutes), the dynamic NAT entry is removed. Should Dynamic
NAT run out of global addresses, it lets Dynamic NAPT handle the connection (which may lead to an unex-
pected behavior).
Dynamic NAT is particularly useful for protocols that do not build on UDP or TCP but directly on IP (e.g.
GRE, ESP). See also section
“NAPT traversal”
on page 131.
Figure 20. Dynamic NAT
Static NAT
Dynamic NAT does not permit hosts on the global network to access hosts on the local network. Static NAT
makes local hosts globally accessible. Static NAT entries map global addresses to local addresses. The global
address must be a configured global NAT address. It cannot be the address of the global interface since this
would break connectivity to the IPLink itself.
Static NAT is particularly useful for protocols that do not build on UDP or TCP but directly on IP (e.g. GRE,
ESP). See also section
“NAPT traversal”
on page 131.
Figure 21. Static NAT
NAPT traversal
Protocols that do not build on UDP or TCP but directly on IP (e.g. GRE, ESP), and protocols that open addi-
tional connections unknown to the NAT/NAPT component (e.g. FTP), do not easily traverse a NAPT.
131.1.1.1 (Global Interface Address)
131.1.1.20 (Global NAT Address)
WAN
192.168.1.40
131.1.1.20
Source Address modified
Destination Address modified
LAN
(Local Interface Address) 192.168.1.1
131.1.1.1 (Global Interface Address)
131.1.1.20 (Global NAT Address)
WAN
192.168.1.40
131.1.1.20
Source Address modified
Destination Address modified
LAN
(Local Interface Address) 192.168.1.1