Virtual Private Networks and IPSec ECE 4112. ECE 4112 - Internetwork Security What is a VPN? VPN Stands for Virtual Private Network A method of ensuring

Virtual Private Networks and IPSec

ECE 4112

ECE 4112 - Internetwork Security

What is a VPN?

• VPN Stands for Virtual Private Network• A method of ensuring private, secure

communication between hosts over an insecure medium using tunneling

• Usually between geographically separate locations, but doesn’t have to be

• Via tunneling and software drivers, computer is logically directly connected to a network that it is not physically a part of


Sidebar: What is tunneling?

• Putting one type of packet inside another

• Both parties must be aware of tunnel for it to work

• Example in next slide - AppleTalk over IP Tunnel


Example: AppleTalk over IP Tunnel

Gateway(AppleTalk Aware)Old Macintosh Old Macintosh

AppletalkIP

Appletalkencapsulated inside

Appletalk

Internet

Gateway(AppleTalk Aware)


What is a VPN? (cont…)

• Uses some means of encryption to secure communications IPSec SSH Software could be written to support any

type of encryption scheme

• Two main types of VPNs – Remote-Access Site-to-Site


What is a VPN? (cont…)

• Remote-Access The typical example of this is a dial-up

connection from home or for a mobile worker, who needs to connect to secure materials remotely

• Site-to-Site The typical example of this is a company

that has offices in two different geographical locations, and wants to have a secure network connection between the two


Remote-Access Example

Network A VPN EnabledGateway

VPN over Internet

Mobile User

Home User


Site-to-Site Example

Network A VPN EnabledGateway

VPN over Internet

Network BVPN EnabledGateway


Why Use a VPN?

• Originally designed as inexpensive alternative WAN over leased lines

• Now mostly used to securely connect computers over the internet

• Convenient• Lot’s of cheap and convenient

protocols are insecure (IP, 802.11, etc) Can now communicate securely over

these insecure protocols


Why Use a VPN? (cont…)

• Example – it can simplify security (what is about to be proposed is not the most secure thing in the world – so don’t

raise your hands and tell how you would make it more secure… it’s just an example)

Assume simple security policy with IP based access management – for example, an FTP server with site-licensed software on it for employees

Before VPN, complicated to allow access to FTP site for telecommuters or traveling employees– Train all employees to use SSH tunnel, etc…

After VPN, employees offsite can still connect using an internal IP address


VPN Advantages

• Improved Security• Consolidation of Scattered Resources• Transparency to Users

If set up properly

• Reduced Cost (vs. Leased Lines)


VPN Disadvantages

• Time Consuming Setup• Possibly Frustrating Troubleshooting• Interoperability with other

Networks/VPNs• Small performance overhead

Should be negligible on today’s hardware


VPN Security

• In academic terms, VPN can provide Confidentiality, Integrity, and Authenticity

• Security against determined hacker (read: academic attacks) depends largely upon underlying protocols used

• Assuming security of SSH, IPSec, or other protocol used, should be secure


How are VPNs set up?

• Many different types of setup• Vary in:

Amount of hardware used vs. amount of software used– All hardware based– All software based– Mixed

Amount of transparency to end-user– Does the user even realize that they are using a

VPN?


How are VPNs set up? (cont…)

• The following is not an exhaustive list Gateway to gateway

– Using two VPN aware Gateways

End host to gateway– End host uses VPN Software

End host to end host– Both hosts use software

End host to concentrator


How are VPNs set up? (cont…)

• SSH over PPP

• SSL over PPP

• Concentrator using IPSec

• Others (PPTP, L2TP, etc)


VPN via SSH & PPP

• Point-to-Point Protocol over a Secure Shell connection

• Establishing a Network Connection Establish an SSH connection

– VPN Client VPN Server

Each have PPP daemons that will communicate through the SSH connection

Viola! A VPN CONNECTION!


VPN via SSL & PPP

• Point-to-Point Protocol over a Secure Socket Layer connection

• Secure Socket Layer Built-in support for Host Authentication Certificates


VPN via SSL & PPP (cont…)

• Establishing a Network Connection Initial Handshake for secure communication “Hello” messages establish:

– SSL Version, support for Cipher suites, and some random data

Key is determined separately from handshake

SSL Connection Complete! Data transferred over the link


VPN via Concentrator

• What is a Concentrator? Concentrator is NOT a gateway or firewall Specialized device that accepts

connections from VPN peers Authenticates clients Enforces VPN security policies Takes overhead of VPN management and

encryption off of gateways and local hosts


VPN via Concentrator (cont…)

• Steps to Establish VPN Set up Concentrator (add users, specify

authentication mechanisms, set IP address ranges, etc)

Install client software Client runs software when wants to be

on VPN


Other Methods

• Point-to-Point Tunneling Protocol Microsoft’s Implementation of VPN Data is first encapsulated inside PPP

packets PPP packets are then encapsulated in GRE

packets and sent over the link

• PPTP uses two connections One for the data being sent Another for a control channel


Other Methods (cont…)

• Any technology can be used Must have hardware or software to support it

• Another example: L2TP on Gateways Layer 2 Tunneling Protocol Supported by routers If two routers support L2TP, and are properly

configured, then VPN is set up between routers Transparent to end user


Intro to IPSec

• Created to add Authentication, Confidentiality, and Integrity to IP traffic

• Designed to combat specific shortcomings in IP

• IPSec is large and implementation is complicated

• What follows is a high-level overview• As will see in lab, need not be used only

as VPN technology – can be stand alone


Intro to IPSec (cont…)

• IP Sec ≠ VPN IP Sec is a protocol used in many VPNs

• Two main modes Transport Tunnel

• Two main services AH (Authentication Header protocol) ESP (Encapsulating Security Protocol)



• Authentication Header protocol Offers Authenticity and Integrity Uses cryptographic hash

– Covers entire packet, including static header fields

If any part of original message changes, it will be detected

Does not encrypt message Can be used to authenticate –

– Prevents IP Spoofing



• Encapsulating Security Protocol Provides Integrity and Confidentiality Encrypts payload If used in tunnel mode, encrypts original

IP header



• Transport Mode

Or

Real IP Header IP Options IPSec Header Payload (For example, TCP and Payload)

ESP Header

Could be either

AH Header

Authenticates Over

Encrypts Over



• Tunnel Mode

Or

GW IP Header IPSec Header Real IP Header Payload (For example, TCP and Payload)

ESP Header

Could be either

AH Header

Authenticates Over

Encrypts Over



• AH and ESP can be used together Tunnel ESP through AH transport packets

• Want to protect cryptographic keys• Internet Key Exchange protocol (IKE)

Secure way to exchange session keys based on shared secret

Can also use certificates (public key cryptography)


Resources

• Books: Building Linux Virtual Private Networks

– Oleg Kolesnikov, Brian Hatch

Linux Server Hacks– Rob Flickenger

Network Security– Charlie Kaufman, Radia Perlman, Mike

Speciner


Resources (cont…)

• Lecture Slides by Wenke Lee (see below)• Websites:

http://vpn.shmoo.com/ http://www.tldp.org/HOWTO/VPN-HOWTO/ http://www.onlamp.com/lpt/a/3009 http://www.cisco.com/warp/public/471/how_vp

n_works.shtml http://www.cc.gatech.edu/classes/AY2004/cs48

03_fall/ipsec_1.ppt http://www.cc.gatech.edu/classes/AY2004/cs48

03_fall/ipsec_2.ppt

http://vpn.shmoo.com/

http://www.tldp.org/HOWTO/VPN-HOWTO/

http://www.onlamp.com/lpt/a/3009

http://www.cisco.com/warp/public/471/how_vpn_works.shtml

http://www.cisco.com/warp/public/471/how_vpn_works.shtml

http://www.cc.gatech.edu/classes/AY2004/cs4803_fall/ipsec_1.ppt




Documents

Virtual Private Networks and IPSec ECE 4112. ECE 4112 - Internetwork Security What is a VPN? VPN Stands for Virtual Private Network A method of ensuring