Source Network Address Translation

In Figure 1, Internal Client does not have a public IP address (private space IP addresses are not routable in the Internet). To allow Internal Client to gain access to Public Server, Syneto will rewrite all packets coming from Internal Client with one of its own public IP addresses:

Client Connects to Public Server: 192.168.1.11 > 2.2.2.2
Syneto rewrites the packet’s source address: 1.1.1.1 > 2.2.2.2
Public server responds to this packet: 2.2.2.2 > 1.1.1.1
Syneto determines that this packet is part of the Internal Clients’ communication and rewrites the packet and sends it to the client: 2.2.2.2 > 192.168.1.11

Figure 1. Source NAT setup

To configure the SNAT rule from the example above (Figure 1), navigate to NAT -> Source NAT menu and introduce the values as specified in Figure 2.We consider that the Corporate LAN is on appliance’s eth2 interface and the internet is on eth0. From a practical point of view we define a source NAT roule which translates all the packets originating from eth2 network (Corporate LAN) and exiting through eth0 interface (to Internet) to be ‘translated’ to External IP. That is, have their source IP address changed from 192.168.1.X to 1.1.1.1.

Figure 2. Defining a source NAT rule for the previous example