Can critical infrastructures rely on the Internet?

The functionality of critical infrastructures (CI) depends more and more on an operative Internet, which has to secure data packet transport even during Internet Exchange Point (IX) failures and "worm" attacks. The paper focuses on the questions: Do priority services for data packets which could be implemented in an Internet Protocol, version 6 (lPv6) world reduce Cl packet loss during IX failures or a worm attack? Do priority services, used by two Cls, lead to competition between their packets during failures and attacks? Under what circumstances do priority services offer a safety margin for Cl packet transport? Simulation shows that priority services produce dialectics of alleviation and risks during an attack. They ensure routing update information thus making routing more stable and thereby reducing packet losses, in particular for Cl data packets. Whereas priority service always matters during Cl failures, that service itself could tie a risk for packet transport if a worm takes up the highest priority class, reserved for routing information, to ensure its unhampered propagation. Therefore, the remedy defenders introduce a crisis, i.e. priority service, which could be abused by those attacking the network. (C) 2005 Elsevier Ltd. All rights reserved.