Multiple IP on the same server howo to idenfity

[NetExpress <NetExpress () infogroup it>]

Hi, the problem is, if I am doing a penetration test from internte to 
many servers, probably there should be some IP ont the same server o 
network adapter like load balancer.
In a report, and to avoid false positive, should be usefull to identify 
which IPs are on the same server, but how?
If I should be in the internal network I am testing I'll use arp to find 
the MAC address of each IP and I should have solved, but from Internet I 
cannot use arp.

From Internet I could use the banner, but this is not sure, I could 
have more then one application server on the same server with n-IP on 
application server A and m-IP on the application server B getting the 
banner should not be the right choise especialy with proxy.

Any idea?

Thanks

Alessandro Fiorenzi