NAT Load Balancing

As an added feature of NAT it can be used to load balance a ‘serverfarm’. The router performing the natting can round robin connection requests to the real servers.

A virtual server address is required. The natting router takes tcp requests received on this address, and the specified ports, and passes them on in a rotary fashion to the servers.

This can be achieved with the following configuration on R2…..


interface FastEthernet0/0
ip address 10.0.0.2 255.255.255.0
ip nat outside
!
interface FastEthernet1/0
ip address 11.0.0.2 255.255.255.0
ip nat inside

ip nat pool REALS 11.0.0.3 11.0.0.4 prefix-length 24 type rotary
ip nat inside destination list VIPACCESS pool REALS
!
ip access-list extended VIPACCESS
permit tcp any host 11.0.0.254 eq telnet

Now when telnetting to 11.0.0.254 from R1, R2 redirects the request to one of the 3 real server addresses

Router_1#telnet 11.0.0.254Trying 11.0.0.254 ... Open
Router_4>

On R2 i examine the nat translation table

Router_2#s ip nat trans

Pro Inside global Inside local Outside local Outside globaltcp 11.0.0.254:23 11.0.0.4:23 10.0.0.1:16630 10.0.0.1:16630

!