Load Balance Incoming Connections
Address pools can also be used to load balance incoming connections. For example, incoming web server connections can be distributed across a web server farm:
web_servers = "{ 10.0.0.10, 10.0.0.11, 10.0.0.13 }"
rdr on $ext_if proto tcp from any to any port 80 -> $web_servers
Successive connections will be redirected to the web servers in a round-robin manner.
As with the NAT example, if the web servers are all placed within a CIDR network block, the source-hash keyword can be used so that connections from a given IP address are always redirected to the same physical web server. Again, this is sometimes necessary to maintain session information while browsing a website.
Все конечно на уровне коннекшенов.... С Уровнем пакетов я погорячился)