If you are hosted by OCLC, then you cannot ExcludeIP private IPs. They are non-routable.
If you are self-hosted, and NAT your private IPs to public IPs using an internet appliance, for example, Squid proxy, to a pool of public Ips, then you can ExcludeIP the private IPs in your EZproxy config file.
Examples of nonroutable or private IP addresses are:
10.0.0.0 - 10.255.255.255 or 10.0.0.0/8 or (10.0.0.0 subnet mask 255.0.0.0)
172.16.0.0 - 172.31.255.255 or 172.16.0.0/12 or (172.16.0.0 subnet mask 255.240.0.0)
192.168.0.0 - 192.168.255.255 or 192.168.0.0/16 or (192.168.0.0 subnet mask 255.255.0.0)