If you let it default, the loopback adapter will get a 169.254.x.y linklocal (APIPA) address which is just fine for local communication. Usually this type of IP means we can’t access the internet but ...
To prevent this you alias the 10.1.1.1 address (cluster address as it is called) on the loopback adapter of the www1 and www2 servers and trick them into to thinking that 10.1.1.1 is a valid address ...