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Firewalls and VPNs at Stanford:

August 22, 2003

Steve Tingley & Sunia Yangtingley@networking, sunia@networkingNetworking Systems

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Topics

• Changing how we look at networking

• Security by protocol stack

• Why protect the network

• Costs

• Specific pros & cons of firewalls

• Specific pros & cons of VPNs

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"Old" Way of Looking at Networks• Open access

• Get all bits from here to anywhere ASAP

• Packet loss is bad in all cases

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"New" Way of Looking at Networks• Only let in/out "good" known traffic

• Block all bad traffic

• Use network device (firewalls/vpns) to make up for insecure transports, insecure applications, unpatched systems

• Use network to partially centralize IT admin in distributed environment

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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

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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

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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

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Network/Transport Layers (Guardposts checking license plates)

• Filter traffic by IP addresses and ports– Router ACLs (may be leaky)– Firewalls

• Require secure protocols or vpn– data encrypted (ssl, ssh) – encrypted data could still be virus or worm

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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

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Why implement security?

• Financial risks– loss of data and reputation– cost of cleaning hacked machines

• Legal risks– Hipaa (medical data), Ferpa (student records)– lawsuits

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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

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Costs• re-educate users accustomed to open net

• training on protocols, apps, security

• staff time– monitor vulnerabilities in firewalls/vpns– monitor traffic for break-ins– troubleshooting - good tight rules can break app if

new revision, etc.

• equipment- hardware and software– firewall, vpn concentrator, vpn client– traffic analysis tools, monitoring/log servers

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Firewall Specifics

• Most common security deployed at network/transport layer

• Helps restrict who talks to who

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Firewall Pros

• For limited staff time and money, may get most amount of security– if firewall placed properly– if staff actively watching network

• Ex.- slammer worm targets port 1434. – adding firewall or router rule to block 1434 is

much faster than patching all machines

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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

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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 in Sys Admins, app

developers, users

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Firewall Costs- #1

• Software & Hardware costs– firewalls, maintenance, support, spares– network analyzer– management/log/monitoring tools– management/log/monitoring servers

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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

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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

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VPN Specifics

• Common way to deal with application data transparency by encrypting

• Another layer of authentication and authorization

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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

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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

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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

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VPN Costs- #1

• Software & Hardware costs– VPN concentrator, maintenance/support, spares– VPN clients, maintenance, support– management/log/monitoring tools– management/log/monitoring servers

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VPN Costs- #2

• Staff costs– Training– Monitoring traffic, vulnerabilities, breakins– VPN client support/upgrades– VPN user administration– Meetings and politics – Documentation, rule change processes

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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

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VPN Technical Issues- #2Split 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

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Stanford VPN Beta

• URL:

• No free client for Mac OS 8 or 9

• Hostname: su-vpn.stanford.edu

• Group Access Information– Group: Stanford– Password: Stanford

Use SUNet ID and password when prompted

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Questions and Feedback

• Thanks to Information Security Services for reviewing technical accuracy and completeness.