Firewall Configuration Strategies

1. Firewall Configuration Strategies Chapter 3

2. Learning Objectives • Set up firewall rules that reflect an organization’s overall security approach • Understand the goals that underlie a firewall’s configuration • Identify and implement different firewall configuration strategies • Employ methods of adding functionality to your firewall

3. Establishing Rules and Restrictions for Your Firewall • Rules give firewalls specific criteria for making decisions about whether to allow packets through or drop them • All firewalls have a rules file—the most important configuration file on the firewall

4. The Role of the Rules File • Establishes the order the firewall should follow • Tells the firewall which packets should be blocked and which should be allowed • Requirements • Need for scalability • Importance of enabling productivity of end users while maintaining adequate security

5. Restrictive Firewalls • Block all access by default; permit only specific types of traffic to pass through

6. Strategies for Implementing a Security Policy • Follow the concept of least privilege • Spell out services that employees cannot use • Use and maintain passwords • Choose an approach • Open • Optimistic • Cautious • Strict • Paranoid

7. Connectivity-Based Firewalls • Have fewer rules; primary orientation is to let all traffic pass through, then block specific types of traffic

8. Overview to Firewall Configuration Strategies • Criteria • Scalable • Take communication needs of individual employees into account • Deal with IP address needs of the organization

9. Scalability • Provide for the firewall’s growth by recommending a periodic review and upgrading software and hardware as needed

10. Productivity • The stronger and more elaborate the firewall, the slower the data transmissions • Important features of firewall: processing and memory resources available to the bastion host

11. Productivity

12. Dealing with IP Address Issues • If service network needs to be privately rather than publicly accessible, which DNS will its component systems use? • If you mix public and private addresses, how will Web server and DNS servers communicate? • Let the proxy server do the IP forwarding (it’s the security device)

13. Firewall Configuration Strategies

14. Firewall Configuration Strategies • Settle on general approaches; establish rules for them • Deploy firewalls, routers, VPN tunnels, and other tools in a way that will implement rules • Use security components to defend against common attacks

15. Using Security Components to Defend Against Attacks

16. Screening Router • Filters traffic passing between one network and another • Simple, minimally secure • Two interfaces—external and internal—each with its own unique IP address • Performs IP forwarding, based on an access control list (ACL)

17. Screening Router

18. Stateful Packet Filtering

19. Dual-Homed Host • A workstation with an internal interface and an external interface to the Internet • Disadvantage • Host serves as a single point of entry to the organization

20. Screened Host • Similar to dual-homed host, but the host is dedicated to performing security functions • Sits exposed on the perimeter of the network rather than behind the firewall • Requires two network connections • Also called a dual-homed gateway or bastion host

21. Screened Host

22. Two Routers, One Firewall • Router positioned on the outside • Performs initial, static packet filtering • Router positioned just inside the network • Routes traffic to appropriate computers in the LAN being protected • Can do stateful packet filtering

23. Two Routers, One Firewall

24. DMZ Screened Subnet • Screened subnet • Network exposed to external network, but partially protected by a firewall • Three-pronged firewall • Three network interfaces connect it to: • External network • DMZ • Protected LAN • Service network • Screened subnet that contains an organization’s publicly accessible server

25. DMZ Screened Subnet

26. Three-Pronged Firewall with Only One Firewall • Advantages • Simplification • Lower cost • Disadvantages • Complexity • Vulnerability • Performance

27. Common Service Network Systems • Those that contain Web and mail servers • Those that contain DNS servers • Those that contain tunneling servers

28. Multiple-Firewall DMZs • Achieve the most effective Defense in Depth • Help achieve load distribution • Added security offsets slowdown in performance • Two or more firewalls can be used to protect • Internal network • One DMZ • Two DMZs • Branch offices that need to connect to main office’s internal network

29. Two Firewalls, One DMZ • Two firewalls used to set up three separate networks (tri-homed firewall) • Internal protected network (behind DMZ) • External private network or service network (within DMZ) • External network (outside DMZ) • Advantage • Enables control of traffic in the three networks

30. Two Firewalls, One DMZ

31. Two Firewalls, Two DMZs • Setting up separate DMZs for different parts of the organization helps balance the traffic load between them

32. Two Firewalls, Two DMZs

33. Multiple Firewalls to Protect Branch Offices

34. Load Distribution Through Layering of Firewalls

35. Reverse Firewalls • Inspect and monitor traffic going out of a network rather than trying to block what’s coming in • Help block Distributed Denial of Service (DDoS) attacks

36. Specialty Firewalls • Protect specific types of network communications (eg, e-mail, instant-messaging) • Examples • Mail Marshal and WebMarshal by Marshal Software • OpenReach includes a small-scale packet-filtering firewall for its VPN • VOISS Proxy Firewall (VF-1) by VocalData • Speedware Corporation sells its own firewall software

37. Approaches That Add Functionality to a Firewall • Network Address Translation (NAT) • Encryption • Application proxies • VPNs • Intrusion detection systems (IDSs)

38. NAT • Converts publicly accessible IP addresses to private ones and vice versa; shields IP addresses of computers on the protected network from those on the outside

39. NAT

40. Encryption • Takes a request, turns it into gibberish using a private key; exchanges the public key with the recipient firewall or router • Recipient decrypts the message and presents it to the end user in understandable form

41. Encryption

42. Application Proxies • Act on behalf of a host; receive requests, rebuild them from scratch, and forward them to the intended location as though the request originated with it (the proxy) • Can be set up with either a dual-homed host or a screened host system

43. Application Proxies • Dual-homed setup • Host that contains the firewall or proxy server software has two interfaces, one to the Internet and one to the internal network being protected • Screened subnet system • Host that holds proxy server software has a single network interface • Packet filters on either side of the host filter out all traffic except that destined for proxy server software

44. Application Proxies on aDual-Homed Host

45. VPNs • Connect internal hosts with specific clients in other organizations • Connections are encrypted and limited only to machines with specific IP addresses • VPN gateway can: • Go on a DMZ • Bypass the firewall and connect directly to the internal LAN

46. VPN Gateway Bypassing the Firewall

47. Intrusion Detection Systems • Can be installed in external and/or internal routers at the perimeter of the network • Built into many popular firewall packages

48. IDS Integrated into Perimeter Routers

49. IDS Positioned Between Firewall and Internet

50. Chapter Summary • How to design perimeter security for a network that integrates firewalls with a variety of other software and hardware components • Rules and restrictions that influence configuration of a security perimeter • Security configurations that either perform firewall functions or that use firewalls to create protected areas