u9.2 Firewalls

u9.2 Firewalls

1. Basics

   • Firewall = Network Security Device intended to restrict access to resources defined by security policy
     • Only restricts or allows access
       • FW is a network security device and provides a point of control between NW segments
         • Typical model is that everything on 1 side is trusted and everything on that side is protected.
           • Other side of the firewall is regarded as untrusted and contains machines from which protection is needed
             • A Firewall must be the only point of connection between trusted and untrusted networks for it to be effective

2. 4 Types of Firewall

   • Packet Filter
     • Layers 3&4
   • Circut Level proxy
     • Layers 3&4
   • Stateful packet filter
     • Layers 3&4
   • Application level proxy
     • Layers 3,4,7
   • First 2 are rarely seen
   • Nearly all modern FW are Stateful / Application level
   • Packet Filter and stateful Packet filter are variations on routers
     • If communication is allowed by the ruleset, packets are allowed through
   • Circut level and application level proxies do not route packets
     • If communication is allowed, then these systems create new packets that are sent to the destination
       • No direct path between source and destination machines