Can Restrict IP work in cases where private IPs are being converted to public IPs?

Asking this from POV of a Drupal user but without good understanding of company firewalls and IP management: In testing Restrict IP and another IP restriction module, it appears this can't work if private/internal computer IPs are being converted to public IPs. Is that true? In testing, it appears to work only with the private/internal IP. Any way around that limitation?