load distribution steps

FIGURE 3 . 4 TCP load distribution steps
1. In Figure 3.4, the PC using outside global IP address 206.2.2.25 attempts to open a TCP
connection to the virtual host at inside global IP address 200.1.1.25.
2. The NAT border router receives this new connection request and creates a new translation,
because one didn’t exist in the NAT table. This allocates the next real inside local IP address
of 10.1.2.25 as the inside local IP address and adds this information to the NAT table using
the same destination port number as the original layer 4 header, port 80.
Note that this example shows only a single inside host, 10.1.2.25, which is not
a practical use for this feature. In production, two or more hosts on the same
inside network would be configured into the rotary pool to service the incoming
requests, with the NAT border router using a round-robin approach to
establishing new connections with these multiple devices running the same
network-accessible applications and data.
3. The NAT border router then replaces the virtual inside global destination IP address with
the selected real inside local IP address and then forwards the packet.
4. The host at the real inside local IP address of 10.1.2.25 receives the packets and responds
to the Internet host through the NAT border router.
5. The NAT border router receives the packet from the server and performs another NAT table
lookup using the inside local IP address and port number as the key. The NAT border router
then translates the source inside local address to the virtual inside global IP address and
10.1.2.25
200.1.1.0
NAT border
router
NAT Table
Inside local IP
10.1.2.25:80
Inside global IP
200.1.1.25:80
Outside global IP
206.2.2.25:3058

forwards the packet. Packets will flow from that real inside local IP address to the Internet
host as long as the TCP session is established, meaning that the translation entry still exists.
6. Assuming there were additional inside hosts with consecutive inside local addresses
assigned to them and entered into the rotary pool on the NAT border router, the next connection
request to the virtual inside global IP address would cause the NAT border router
to allocate 10.1.2.26 for the inside local IP address. This continues until all IP addresses in
the pool are used; then the router starts at the beginning of the pool.