1. 1 Firewalls at Stanford: May 14, 2004 Sunia Yang sunia@networking The Group Formerly Known as Networking

2. 2 Topics Changing how we look at networking –Security by protocol stack –Why protect the network –Specific pros & cons of firewalls –Specific pros & cons of VPNs Living with firewalls –Firewall topology –Firewall rules –User education, monitoring, documenting, auditing –Troubleshooting Building firewall exercise

3. 3 Networks: Past & Future Past –Just get the bits there! –Open highway system –Trust Future –Patriot act –Who are you? What are you doing? –Make up for other layer's security weaknesses by centralizing security into network layer –More bureaucracy, process

4. 4 Security by Protocol Stack Firewalls and VPNs are just part of a total security approach –Firewall would not have caught bugbear-b virus –Firewall at Stanford border would not have prevented Windows RPC exploits

5. 5 Physical Layer Security (Fences) "If you can touch it, you can hack it" –Lock up servers, network closets Wireless- –firewall defeated if wireless behind firewall –allowing unencrypted wireless session through firewall defeats data security

6. 6 Data layer (bus vs star topology) Switches as security device –isolates conversations- sniffer protection may misbehave and "leak" –block by hardware address not possible in all switches –hardcode hw address to port- tedious, unscalable

7. 7 Network/Transport Layers (Guardposts checking license plates) Filter traffic by IP addresses and ports –Router ACLs (may be leaky) –Firewalls –Host IP filters Require secure protocols or vpn –data encrypted (ssl, ssh) –encrypted data could still be virus or worm

8. 8 Application Layer (Stuff inside car) Design in security –good architecture- 3 tier –no clear text passwords –secure transports Proxy "firewalls" –screens traffic at app layer before passing to real application Good sys admins –patch, antivirus-software –turnoff unused services

9. 9 Why implement security? Financial risks –loss of data and reputation –cost of cleaning hacked machines Legal risks –Hipaa (medical data), Ferpa (student records) –Lawsuits "Cuz they said so…"

10. 10 Why firewalls/vpns? Physical and data layer security is critical –mostly implemented already (except wireless) Too many badly architected apps on market Often best return of security for given staff, time and money

11. 11 Firewall Cons- #1 Inconvenience to users –re-educate users –good rules > minor changes may break app –need good communication, docs and response –protective rules constrain traffic ex. protecting workstations by denying incoming connections may break peering apps

12. 12 Firewall Cons- #2 Incomplete security –Firewall does not protect needed server ports e.g., if running IIS server, need to open hole for http. IIS vulnerability still must be patched. But may prevent hacker from reaching backdoor –Does not protect against email viruses/worms –May lead to complacency –Hard to firewall if app uses random ports

13. 13 Firewall Costs- #1 Software & Hardware costs –firewalls, maintenance, support, spares –network analyzer –management/log/monitoring tools –management/log/monitoring servers

14. 14 Firewall Costs- #2 Staff costs –Training –Traffic analysis and rule development –Monitoring traffic, vulnerabilities, breakins –Rule changes- proactive or reactive? –Meetings and politics –Documentation, rule change processes

15. 15 Firewall Technical Issues Manageable rule set vs. many exceptions False positives –ex. Monitoring pings might look like icmp attack Hard to secure port-hopping apps- VPN? Session timeout limits Server initiates new session to client (AFS) Reply to client from different IP (load balancers)

16. 16 VPN Specifics Common way to deal with application data transparency by encrypting packets Another layer of authentication and authorization Note:Board Diagram

17. 17 VPN Pros With limited staff time and money, may get most application layer security Sometimes can be used to enforce patch level of client operating systems

18. 18 VPN Cons- #1 Inconvenience –not all VPN clients compatible or can co-exist –VPN clients fiddle with host's tcp/ip stack may break some apps –may break IP dependent services –split tunnel issues- discussed later

19. 19 VPN Cons- #2 Incomplete security –Does not protect if client machine hacked in fact, provides encrypted tunnel for hacker –May lead to complacency in users, sys admins, app developers –Has its own security issues

20. 20 VPN Costs- #1 Software & Hardware costs –VPN concentrator, maintenance/support, spares –VPN clients, maintenance, support –management/log/monitoring tools –management/log/monitoring servers

21. 21 VPN Costs- #2 Staff costs –Training –Monitoring traffic, vulnerabilities, breakins –VPN client support/upgrades –VPN user administration –Meetings and politics –Documentation, rule change processes

22. 22 VPN Technical Issues- #1 Scalability issues Encryption overhead affects throughput VPN client picks up new IP Software vs hardware VPN clients –cost vs convenience vs compatibility

23. 23 VPN Technical Issues- #2 Split Tunnel only traffic to specific servers is encrypted pros- performance –less encryption overhead –less traffic to central VPN concentrator cons- security –if client host is hacked, hacker can control VPN session

24. 24 Living with Firewalls- Mantras "Know Thy Network Traffic" –If you don't know it now, you're going to learn it the hard way "Know Thy Servers" –ditto

25. 25 Living with Firewalls- Steps Design topology Firewall Rules Enforce rules Monitor, document, audit Troubleshooting

26. 26 Laying out Firewall Topology Group servers by –Sensitivity and type of data –Security level (don't put petty cash in the safe) –Production vs development Especially as projects are out-sourced, don't want our data somewhere else in the world Sharing switches –Generally, databases or servers actually holding data should be on separate switch (no VLANs)

27. 27 Basic Firewall Topology FW = firewall SW = switch S = server FW1 S1S2S3 SW2 S7S8S9 Zone 2 Ex. Web Servers Zone 4 Ex. Database Servers Zone 1 Firewall can only filter between zones by IP address and port Applications often use a well-known port S4S5S6 Zone 3 Ex. App Servers vlan 20 vlan 30 SW1

28. 28 Firewall Rules- Part 1 Rule requires the following pieces: Action: Permit, Deny, Tunnel Source IPs: Client, VPN Client, Admin, Hacker Destination IPs: Servers Destination Port: 80(web), 25(smtp), etc. Port Type: tcp, udp

29. 29 Firewall Rules- Part 2 Examples: Allow 10.0.1.5 to 171.64.7.77 on udp port 53 (DNS) Allow 10.0.1.0/24 to 10.0.2.10 on tcp port 25 (SMTP) Deny 10.0.1.0/24 to any on tcp port 25 (SMTP) Sources: servers, clients, vpn clients, hackers (remember the last one when you are writing rules!!!!) Rules applied in order To document or not to document- that is the question! Note: Board Diagram

30. 30 Categories of Rules- Part 1 Host DNS, NTP Administration Monitoring – snmp, email, icmp Remote session - telnet, ssh, rsh, citrix Authentication - sident, kerberos, MS auth Maintenance - upgrades, virus, rebuilds, backup, file transfer Central systems –Microsoft domains/AD, afs, nfs

31. 31 Categories of Rules- Part 2 Application Client: Web services Server to server: db sharing, file transfer, app to db Development Environments- training, development, etc Server to server: db sharing, file transfer, app to db Application build Developer access- in-house, remote

32. 32 Educating Users Firewalls are inconvenient and bureaucratic Can't ignore the network anymore Develop process around requesting and approving rules Application owner owns security of application? Security and firewall team may comment on quality of rules

33. 33 Enforcing Rules When developing rules, usually last rule is –permit any to any on port any –Catches any unknown traffic To enforce rules, disable or delete "permit any any" rule.

34. 34 Monitoring, Documentation, Auditing Monitoring- alarm system is still on Documentation- balance between usability and security- policy decision Security auditing- make sure rules are good and rules still work!

35. 35 Troubleshooting A can't reach B which is behind firewall –Try ping first (allowed by default at Stanford on FWs) If fails, check IP addr, physical connection –Try telnet to desired port If okay, then not a firewall issue- probably app layer –Message like "Connected to B" If fails, depends on message: –"Connection closed by foreign host" or "Connection refused" means B rejects A –Hangs with message "Trying B", finally getting message like "Unable to connect to remote host: timed out" means that port is not reachable- possibly firewall –Run "netstat" on B to see if ports are open

36. 36 Common Problems ~80% requests to check firewall show that firewall is not the problem ~10% of time, previously unknown traffic ("know thy app") has no appropriate rule Typos, miscommunication Host IP changes, thus breaking rule

37. 37 Team Exercise/Lab

38. 38 Questions and Feedback