User manual

Chapter 4 - Layer 3 Command Set - IP Networking Nat Command (Network Address Translation)
Alvarion BreezeNET B130/B300 GigE 197 Operational User Manual
4.14.1 General Description
NAT allows solving to the certain extent the problem IPv4 address space
exhausting. It means that several computers in the given LAN may connect to
Internet via the same public IP address. NAT-module receives outgoing
IP-packets, modifies sender's IP address to the public IP address and forwards it
to Internet. Sender's IP address is modified in such a way that it is possible to
identify the sender when IP packet received on the LAN incoming interface and to
forward the IP packet to the initial sender. NAT-module is similar to natd and
libalias from FreeBSD.
As its known (rfc1918), some part of IPv4 address space is reserved for using in so
called private IP networks (private internets).
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
Internet backbone routing protocols do not advertise these addresses, which
allows to use the same addresses in different Internet segments. These addresses
are used by ISP's and enterprises to build internal transport environment and/or
to connect small subscriber communities.
Perhaps, when connecting your LAN to Internet, ISP will suggest you to minimize
the number of really existing IP-addresses in order to save its own address space.
Common user needs very limited set of well-known services: WWW, FTP, ICQ,
Telnet, SMTP, Games. This is quite accessible using private internets and NAT.
Besides, there are dedicated proxy-servers for concrete services which fit better for
this task. E.g. for HTTP and FTP it is better to use caching proxy server Squid.
If you decided to use IP-telephone based on H.323 standard, then it is better to
use private internets. We have H.323 support module in our NAT version.
So, we have the following scenario: using private internets in your LAN and you
have a limited number of public IP-address.
4.14.2 Commands Description
nat local_acl $NAME aliasIP
This command sets the real (public) IP-address which will be used for address
translation. In order for the routing protocols to work normally, this address must
be assigned to any physical interface of the device. The device has at least two
physical interfaces: Ethernet (eth) and radio (rf). Usually, the system is linked to