Problems with Kerberos authentication over internet

[arpit.orb]

Hi,

I am using Kerberos over internet by assigning a public IP to KDC. However, I have following doubts:

1. Why is it that Kerberos is not deployed as preferred authentication mechanism over internet ? I understand that some reasons are vulnerability if KDC over port 88, address in tickets etc. But is there any other technical reason for which Kerberos should not be used over public network ?

2. Are there any known issues with and without VPN ? 

Thanks,
Arpit