Firewalls are an important tool in the provision of network security. Packet filtering firewalls are configured by providing a set of rules that identify how to handle individual data packets that arrive at the firewall. In large firewall configurations, conflicts may arise between these rules. Argumentation provides a way of handling such conflicts that illuminates their origin, and hence can help a system administrator understand the effects of a given configuration. The authors look in particular at the use of a system of meta-level argumentation for firewall configuration, showing how it makes conflicts and their origins especially clear, and showing how different instantiations of a meta-level argumentation system provide alternative ways to resolve conflicts.