Network Security Essentials — Notes10. Firewall

Firewall’s Goals

  1. All traffic must pass through the wall

  2. Only authorized traffic is allowed to pass

  3. Immune to penetration


  1.Service Control    — "This IP is blocked"

  2.Direction Control  — "Currently we only allow outside traffic"

  3.User Control       — "You are not allowed to get in"

  4.Behavior Control   — "You can’t send spams to me"

Types of Firewall

   1.Packet-filtering Router — Filtering based on info in TCP/IP headers, including

      a.Source IP

      b.Destin IP

      c.TCP Port number

      d.IP Protocol Field

      e.Rooter’s Interface  (Interface for inside traffic or for outside traffic)

   2.Application-level Gateway = Proxy, inspecting application-level messages

      a.Advantage: More secure than packeting-filter

      b.Disadvantage: Too much additional overhead

   3.Curcuit-level Gateway 

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