Abstract: The study of the firewall to the network worm propagation concentrates mainly in the single subnet or the small
scale enterprise network. In view of the control of the firewall to network worms under many subnets, a model of the worm
propagation and control based on firewall is proposed. By analyzing network worm propagation in a single subnet and cross
propagation between subnets, this model reduces the cross infection rate between subnets and suppresses network worm
propagation through the firewall. Uniform scanning and local scanning worm propagation are simulated by this model. Results
show that the effect of the firewall on uniform scanning worm is good; when the local scan rate is relatively high, the
effect of the firewall on local scanning worm is relatively poor, which is consistent with the real situation.

Key words: firewall, worm virus, network secruity