Overview of VPN and IPSec Technologies

1
Lecture 2
2
Overview of VPN and IPSec Technologies

• Chapter 2

3
Lecture 2 Objectives

• Understand Virtual Private Network Technologies
• List who benefits from VPNs
• List primary reasons for VPNs and typical
  applications of VPNs
• List 3 VPN benefits
• Identify 3 basic VPN categories
• List 4 Cisco VPN products
• Describe Management Software
• Recognize IPSec protocols and protocol framework
• Define 2 VPN Modes of Operation

4
Lecture 2 Objectives (cont)

• Describe Security Associations (SA)
• Define Message Encryption and Message Integrity
  (HMAC)
• List 3 Peer Authentication methods
• Define Key Management
• Identify the Key Exchange of Choice
  Diffie-Hellman
• Recognize Certificate Authorities (CAs)
• Authenticate IPSec Peers Form Security
  Associations
• List the 5 step process on how IPSec works

5
Overview of VPNs and IPSec

• Virtual Private Network
• Service offering secure communication across a
  public network
• Cisco defines a VPN as an encrypted connection
  between private networks over a public network,
  such as the Internet
• Three types of VPNs
• Remote Access
• Site to Site
• Firewall Based

6
VPNs Benefit the following

• Telecommuters
• Mobile users
• Remote offices
• Business partners
• Clients
• Customers

7
Primary Reasons for VPNs

• Security
• Reduced cost
• All size businesses can quickly and easily
  implement secure VPNs using IPSec or other
  protocols.

8
Typical VPN Applications

• E-mail
• Web browsers
• Client/server programs

9
Benefits of Deploying VPNs

• Cost savings
• Security
• Scalability

10
Cost Savings

• Elimination of expensive dedicated WAN circuits
• Elimination of banks of dedicated modems
• ISPs provide Internet connectivity from anywhere
  at any time.

11
Security

• Private on public infrastructure
• Encryption
• Authentication

12
Scalability

• With VPN technologies, new users can be easily
  added to the network.
• Corporate network availability can be scaled
  quickly with minimal cost.
• A single VPN implementation can provide secure
  communications for a variety of applications on
  diverse operating systems.

13
VPNs - Three Basic Categories

• Remote access
• Site-to-Site Intranet VPNs
• Extranet

14
VPN TypesRemote Access

• Remote Access
• Telecommuters, mobile workers, and remote offices
  with minimal WAN bandwidth

Figure 2.2 Remote Access VPNs
15
VPN TypesRemote Access (cont.)

• Remote Access
• Targeted at mobile users and home telecommutes

16
Advantages of Remote Access

• Modems and terminal servers, and their associated
  capital costs, can be eliminated.
• Long-distance and 1-800 number expenses can be
  dramatically reduced as VPN users dial in to
  local ISP numbers, or connect directly through
  their always-on broadband connections.
• Deployments of new users are simplified, and the
  increased scalability of VPNs allows new users to
  be added without increased infrastructure
  expenses.

17
Disadvantages of Remote Access

• IPSec has a slight overhead because it has to
  encrypt data as they leave the machine and
  decrypt data as they enter the machine via the
  tunnel.
• For users with analog modem connections to the
  Internet at 40 kbps or less, VPNs can be slow
• IPSec is sensitive to delays. Because the public
  Internet infrastructure is used, there is no
  guarantee of the amount of delay that might be
  encountered
• Users might need to periodically reestablish
  connections if delay thresholds are exceeded.

18
Types of VPNsSite-to-Site

• Site to Site
• Used to connect remote offices and branch offices
  to the headquarters internal network over a
  shared infrastructure

Figure 2.3 Intranet VPNs
19
Types of VPNsSite-to-Site (cont.)

• Site to Site
• Used to connect Corporate Sites, past connections
  were through Leased Lines or P2P connections

20
Benefits of Site-to-Site Intranet VPNs

• Reduction of WAN costs, especially when used
  across the Internet.
• Partially or fully meshed networks can be
  established, providing network redundancy across
  one or more service providers.
• Ease of connecting new sites to the existing
  infrastructure.

21
Types of VPNsBusiness-to-Business Extranet

• Business-to-Business Extranet
• Used to give corporate network access to
  customers, suppliers, business partners, or other
  interested communities who are not employees of
  the corporation

Figure 2.4 Extranet VPNs
22
Business-to-Business Extranet VPNs

• Security policies can limit access by
• Protocol
• Ports
• User identity
• time of day
• source or destination address
• other controllable factors

23
Cisco VPN Products

• Routers
• Firewalls
• VPN concentrators
• Clients

24
Cisco VPN Routers

• The best choice for constructing
• Site-to-Site Intranet VPNs
• Business-to-Business Extranet VPNs
• See table 2-3 on pages 27-28 for complete listing

25
Cisco VPN Routers IOS Software

• Delivers multicast
• Routing
• Multiprotocol
• Quality of Service (QoS)
• Integrated DSL and cable modems
• Special VPN modules (Network Modules)
• Encryption
• free memory
• CPU cycles

26
Cisco PIX Firewalls

• Special VPN modules (Network Modules)
• Encryption
• free memory
• CPU cycles
• See table 2-4 on page 29 for complete listing

27
Cisco VPN 3000 Concentrators

• The best choice for constructing
• Remote Access VPNs
• See table 2-5 on page 31 for complete listing

28
Cisco VPN 3000 Concentrators (cont.)

• High-performance
• Scalable
• Offer high availability
• State-of-the-art encryption
• Authentication techniques
• Scalable Encryption Processor (SEP) modules can
  be easily used to add capacity and throughput.

29
Cisco VPN 3000 Concentrators (cont.)

• Support small offices of 100 or fewer VPN
  connections to large enterprises of 10,000 or
  more simultaneous VPN connections
• Redundant and nonredundant configurations are
  available
• Support wireless clients
• Personal Digital Assistants (PDAs)
• Smart Phones

30
Cisco VPN Client (Unity Client)

• No extra cost
• (with Cisco VPN 3000 Series Concentrators)
• Relatively easy to configure
• Can be preconfigured for mass deployments
• Scalable

31
Cisco VPN Client supports

• Linux
• Solaris
• MAC OS
• Windows 95
• Windows 98
• Windows Me
• Windows NT 4.0
• Windows 2000
• Windows XP

32
Wireless Client Support

• Trial copy of Certicom Corporations Movian VPN
  Client
• Elliptic Curve Cryptosystem (ECC)compliant
• New Diffie-Hellman group

33
Cisco Internet Mobile Office

• Cisco Mobile Office On The Road is a global
  collaborative effort
• Provides secure, high-speed Internet and intranet
  access from public facilities such as airports
  and hotels

34
Management Software

• Cisco VPN Device Manager
• CiscoWorks 2000
• Cisco Secure Access Control Server (ACS)
• CiscoWorks VPN/Security Management Solution (VMS)

35
Cisco VPN Device Manager

• Installed directly into a supporting routers
  flash memory
• Supported on Cisco 7100, 7200, and 7400 Series
  Routers

36
Cisco Secure Access Control Server (ACS)

• Ciscos Authentication, Authorization, and
  Accounting (AAA) server
• TACACS
• RADIUS.
• Web-based, graphical interface, easy to install
  and administer.
• Supported on routers, firewalls, concentrators,
  VPNs, switches, DSL and cable solutions, voice
  over IP (VoIP), and wireless solutions.

37
CiscoWorks VPN/Security Management Solution (VMS)

• Highly scalable solution for configuring,
  monitoring, and troubleshooting remote access,
  intranet, and extranet VPNs for small- and
  large-scale VPN deployments

38
IPSec

• Network layer
• Protects and authenticates IP packets between
  participating IPSec peers
• Not bound to any specific encryption or
  authentication algorithms, keying technology, or
  security algorithms
• Framework of Open Standards
• Provides CIA (confidentiality, Integrity, and
  Authentication)

39
IPSec Protocols

• A collection of open standards
• www.ietf.org/html.charters/ipsec-charter.html
• Data confidentiality
• Data integrity
• Data authentication
• Works at the IP layer
• Can use the Internet Key Exchange (IKE) protocol

40
Things to Remember with IPSec

• IPSec supports High-Level Data-Link Control
  (HDLC), ATM, Point-to-Point Protocol (PPP), and
  Frame Relay serial encapsulation.
• IPSec also works with Generic Routing
  Encapsulation (GRE) and IP-in-IP (IPinIP)
  Encapsulation Layer 3 tunneling protocols. IPSec
  does not support the data-link switching (DLSw)
  standard, source-route bridging (SRB), or other
  Layer 3 tunneling protocols.
• IPSec does not support multipoint tunnels.

41
Things to Remember with IPSec

• IPSec works strictly with unicast IP datagrams
  only. It does not work with multicast or
  broadcast IP datagrams.
• IPSec provides packet expansion that can cause
  fragmentation and reassembly of IPSec packets,
  creating another reason that IPSec is slower than
  CET.
• When using NAT, be sure that NAT occurs before
  IPSec encapsulation so that IPSec has global
  addresses to work with.

42
IPSec Protocols

• IP Security Protocol (IPSec)
• Authentication Header (AH)
• Encapsulating Security Payload (ESP)
• Message Encryption
• Data Encryption Standard (DES)
• Triple DES (3DES)
• AES Advanced Encryption Standard, developed to
  replace DES, 128 and 256 bit
• Message Integrity (Hash) Functions
• Hash-based Message Authentication Code (HMAC)
• Message Digest 5 (MD5)
• Secure Hash Algorithm-1 (SHA-1)

43
IPSec Protocols (cont.)

• Peer Authentication
• Rivest, Shamir, and Adelman (RSA) Digital
  Signatures
• RSA Encrypted Nonces
• Key Management
• Diffie-Hellman (D-H) DH1, DH2, DH5
• Certificate Authority (CA)
• Security Association
• Internet Key Exchange (IKE)
• Internet Security Association and Key Management
  Protocol (ISAKMP)

44
IPSec Protocols (Purely IPSEC)

• Authentication Header (AH)
• Encapsulating Security Payload (ESP)
• IKE and IPSec negotiate encryption and
  authentication services between pairs. This
  negotiation process culminates in establishing
  Security Associations (SAs)

45
IPSec ProtocolsSecurity Associations (SAs)

• SAs are stored in a Security Association Database
• Each SA is assigned a Security Parameters Index
  (SPI) number
• combined with the destination IP address and the
  security protocol (AH or ESP), uniquely
  identifies the SA.

46
IPSec Protocols Authentication Header (AH)

• Authentication Header (AH)
• Provides
• Data integrity
• Data origin authentication
• Uses a keyed-hash mechanism
• An optional anti-replay service
• Does not provide
• Encryption
• Which means that the packets are sent as clear
  text

47
IPSec Protocols Authentication Header (AH)

• Authentication Header (AH)

Figure 2.5 AH Header in IPSec Datagram
48
IPSec Protocols Encapsulating Security Payload
(ESP)

• Encapsulating Security Payload (ESP)
• Provides
• Confidentiality by enabling encryption of the
  original packet
• Data origin authentication
• Integrity
• Anti-replay service
• Some limited traffic flow confidentiality

49
IPSec Protocols Encapsulating Security Payload
(ESP)

• Encapsulating Security Payload (ESP)

Figure 2.6 EPS Encapsulation Process
Figure 2.7 Encapsulating Security Payload
50
Anti-Replay

• Ensure that IP packets cannot be intercepted by a
  third party or man in the middle and then be
  changed and reinserted into the data stream
• AH (Authentication Header) and ESP (Encapsulating
  Security Payload) are anti-replay tactics
• Keep track of sequence numbers allocated to
  packets
• When security association is established sequence
  numbers are set to 0
• Packets are then encrypted and numbered starting
  at 1
• Receiver verifies packet sequence number is not
  the same as the one it previously received
• AH does this by default
• ESP does it by turning on authentication (MD5 or
  SHA-1)

51
Modes of VPN Operation

• Transport mode
• Tunnel mode

52
Modes of VPN Operation Transport Mode

• Transport
• Protects the packets payload, higher-layer
  protocols
• Leaves the original IP address in the clear
• The original IP address is used to route the
  packet through the Internet
• Used between two hosts
• Provides security to the higher-layer protocols
  only

53
Modes of VPN Operation Transport Mode (cont.)

• End-to-end connections between hosts or devices
  acting as hosts
• AH Transport mode does not support NAT
• because changing the source IP address in the IP
  header causes authentication to fail
• If you need to use NAT with AH Transport mode,
  you must ensure that NAT happens before IPSec

54
Modes of VPN Operation Transport Mode (cont.)

• ESP Transport mode

• AH Transport mode

Figure 2.9 ESP Transport Mode
Figure 2.8 AH Transport Mode
55
Modes of VPN Operation Tunnel Mode

• Tunnel
• Used when either end of the tunnel is a security
  gateway ( Concentrator, router, or a PIX Firewall
• Used when the final destination is not a host,
  but a VPN gateway
• The security gateway encrypts and authenticates
  the original IP packet. A new IP header is then
  appended to the front of the encrypted packet.
  The new outside IP address is used to route the
  packet through the Internet to the remote end
  security gateway
• Provides security for the whole original IP
  packet.

56
Modes of VPN Operation Tunnel Mode (cont.)

• Used between gateways
• Cisco IOS Software routers
• Cisco PIX Firewalls
• Cisco VPN 3000 Series Concentrators
• also typically used when a host connects to one
  of these gateways
• AH Tunnel mode does not support NAT

57
Modes of VPN Operation Tunnel Mode

• ESP Tunnel mode

• AH Tunnel mode

Figure 2.11 ESP Tunnel Mode
Figure 2.10 AH Tunnel Mode
58
ESP

• ESP supports NAT in either Tunnel or Transport
  mode
• ESP supports encryption, AH does not
• ESP supports authentication with ESP HMAC
  service.

59
Security Associations (SA)

• Negotiation process to select a matching set of
• Algorithms for authentication
• Encryption
• Hashing
• SA lifetime.
• Ensure data integrity and source authenticity,
  provide encryption, or do both

60
Security Associations (SA) (cont.)

• SAs are simplex
• Establishing conversations between peers requires
  two IPSec SAs
• one going and one coming
• IPSec SAs are also protocol specific
• Using both AH and ESP between security pairs, you
  need separate SAs for each

61
Existing Protocols Used in the IPSec Process

• IPSec makes use of numerous existing encryption,
  authentication, and key exchange standards. This
  approach maintains IPSec as a standards-based
  application, making it more universally
  acceptable in the IP community.

62
Existing Protocols Used in the IPSec Process
(cont.)

• Confidentiality
• Uses encryption
• Clear text is changed into ciphertext on public
  internet
• 2 types of encryption keys
• Asymmetric
• Use one key to encrypt and another to decrypt
  i.e. RSA
• Symmetric
• Use the same key to encrypt and decrypt i.e. DES,
  3DES, AES
• The longer the key the stronger the encryption

63
Message Encryption

• Data Encryption Standard (DES)
• 56-bit key
• Triple Data Encryption Standard (3DES or Triple
  DES)
• Produces an aggregate 168-bit key, providing
  strong encryption
• Performs an encryption process, a decryption
  process, and then another encryption process,
  each with a different 56-bit key

64
Message Integrity (hashing)

• Hash is created, any deviation means that the
  message has been altered
• Message Digest 5 (MD5)
• Secure Hash Algorithm-1 (SHA-1)
• Hashed Method Authentication Code (HMAC)
• HMAC was developed to add a secret key into the
  calculation of the message
• MD5 creates a shorter message digest than does
  SHA-1 and is considered less secure but offers
  better performance

65
Message Integrity (hashing) (cont.)

• To guard against modification of data, hashes are
  used to ensure data has not been modified
• HMAC (Hash based Message Authentication Code)
• Hashes must match on both sides of communication
  to ensure data has not been altered
• 2 main algorithms used with IPSec are MD5 and
  SHA-1

66
Message Integrity (hashing) HMAC
67
Peer Authentication

• Digital Signatures
• The signature is authenticated by decrypting the
  signature with the senders public key
• RSA is used most common and commercially
• DSA is used by the government
• Peer Authentication methods
• Pre-shared Keys
• RSA Signatures
• RSA Encrypted Nonces random number generated by
  peers

68
Peer Authentication Preshared Keys

• The process of sharing preshared keys is manual
• This method is fairly secure, but it does not
  scale well to large applications

69
Peer Authentication RSA Digital Signatures

• Certificate Authority (CA) provides RSA digital
  certificates upon registration with that CA
• These digital certificates allow stronger
  security than do preshared keys
• When an RSA digital certificate is requested, a
  public and a private key are generated

70
Peer Authentication RSA Encrypted Nonces

• A nonce is a pseudorandom number.
• RSA encrypted nonces permit repudiation of the
  communication
• Either peer can plausibly deny that it took part
  in the communication
• Cisco is the only vendor that offers this form of
  peer authentication

71
Key Management

• Five permanent keys are used for every IPSec peer
  relationship
• Two are private keys
• Two are public keys
• The fifth key is the shared secret key. Both peer
  members use this key for encryption and hashing
  functions
• This is the key created by the Diffie-Hellman
  protocol
• Establishing conversations between peers requires
  two IPSec SAs

72
Key Management How Do We Get Our Keys?

• Keys can be exchanged in any manner necessary
• Key Exchange of Choice? Diffie-Hellman
• Provides a way for two peers to establish a
  shared secret key that only they know, although
  they are communicating over an insecure channel
• Security is not an issue with DH key exchange.
  Although someone might know a users public key,
  the shared secret cannot be generated, because
  the private key never becomes public

73
Diffie-Hellman Protocol

• Each peer generates a Public/Private Key pair
• Private Key is NEVER shared
• Each peer combines the others public key with
  its own private key and computes the same shared
  secret number
• The shared secret number is then converted into a
  shared secret key and the shared secret key is
  never exchanged over the insecure channel

74
Diffie-Hellman Protocol (cont.)

• Asymmetrical key exchange process in which peers
  exchange different public keys to generate
  identical private keys
• Diffie-Hellman is a clean process
• Asymmetric key encryption processes are much too
  slow for the bulk encryption required in
  high-speed VPN circuits
• Diffie-Hellman protocol has been relegated to
  creating the shared secret key used by symmetric
  key encryption protocols.

75
Diffie-Hellman Protocol (cont.)

• Diffie-Hellman provides an elegant solution for
  providing each peer with a shared secret key
• Peers that use symmetric key encryption protocols
  must share the same secret key
• Symmetric key encryption processes then use the
  shared secret key for encryption or
  authentication of the connection

76
Diffie-Hellman Protocol (cont.)
77
Certificate Authorities (CAs)

• Are a trusted entity for issuing and revoking
  digital certificates and for providing a means to
  verify the authenticity of those certificates
• CAs are usually third-party agents such as
  VeriSign or Entrust
• For cost savings, you could also set up your own
  CA using Windows 2000 Certificate Services.

78
Authenticating IPSec Peers Forming Security
Associations

• The protocol that brings all the previously
  mentioned protocols together is the Internet Key
  Exchange (IKE) Protocol
• IKE operates in two separate phases when
  establishing IPSec VPNs
• IKE Phase 1, it is IKEs responsibility to
  authenticate the IPSec peers, negotiate an IKE
  security association between peers, and initiate
  a secure tunnel for IPSec using the Internet
  Security Association and Key Management Protocol
  (ISAKMP)
• In IKE Phase 2, the peers use the authenticated,
  secure tunnel from Phase 1 to negotiate the set
  of security parameters for the IPSec tunnel.

79
IKE Phase 1

• Encryption algorithm56-bit DES (default) or the
  stronger 168-bit 3DES.
• Hash algorithmMD5 (default) or the stronger
  SHA-1.
• Authentication methodPreshared keys, RSA
  encrypted nonces, or the most secure, RSA digital
  signatures (also the default).
• Key exchange method768-bit Diffie-Hellman Group
  1 (default) or the stronger 1024-bit
  Diffie-Hellman Group 2.
• IKE SA lifetimeThe default is 86,400 seconds or
  1 day. Shorter durations are more secure but come
  at a processing expense.
• Must be identical on the prospective peer

80
IKE Phase 2 (IPSec Transform Sets)

• IPSec protocolAH or ESP
• Hash algorithmMD5 or SHA-1 (These are always
  HMAC assisted for IKE Phase 2.)
• Encryption algorithm if using ESPDES or 3DES
• The AH Protocol is seldom used in production
  environments today. SHA-HMAC and MD5- HMAC are
  now available to provide additional packet
  integrity for ESP. A second argument for not
  using AH is that AH does not support NAT or PAT

81
IPSec Transform Sets

• IPSec parameters are grouped into predefined
  configurations called transforms.
• The transforms identify the IPSec protocol, hash
  algorithm, and when needed, the encryption
  algorithm
• Only a handful of valid transforms are available
  they are identified on the next slide
• A specific IPSec tunnel can support up to three
  transform sets, one AH and up to 2 ESPs, as
  listed on page 56

82
IPSec Transforms
83
How IPSec Works IPSec Preparation Steps

• Most projects go much easier if you spend some
  careful planning time before you begin. The same
  is true for implementing IPSec security
• Step 1 Establish an IKE policy
• Step 2 Establish an IPSec policy
• Step 3 Examine the current configuration
• Step 4 Test the network before IPSec
• Step 5 Permit IPSec ports and protocols

84
How IPSec Works The Five-Step Process of IPSec

• Step 1 Interesting traffic initiates the setup of
  an IPSec tunnel.
• Step 2 IKE Phase 1 authenticates peers and
  establishes a secure tunnel for IPSec
  negotiation.
• Step 3 IKE Phase 2 completes the IPSec
  negotiations and establishes the IPSec
  tunnel.
• Step 4 Once the tunnel has been established,
  secured VPN communications occur.
• Step 5 When there is no more traffic to use
  IPSec, the tunnel is torn down, either
  explicitly or through timeout of the SA
  lifetimes.

85
How IPSec WorksStep 1

• Define Interesting Traffic
• What traffic should be protected
• Use access-lists to determine traffic
• Outbound ACLs select protected, Inbound filters
  traffic that should have been protected
• Security policy dictates Access Control Lists
  (ACL)
• Peers must contain the same access lists, and you
  can have multiple access lists for different
  purposes between peers
• ACLs are called crypto ACLs

86
How IPSec WorksStep 1 (cont.)

• Permit and Deny keywords have a different purpose
  for crypto ACLs
• Permit - Allows for authentication, encryption,
  or both.
• Deny - Bypasses IPSec and puts the clear-text
  packet on the wire to the destination

Table 2.10 Crypto ACL Actions
87
How IPSec WorksStep 1 (cont.)

• Outbound ACLs

Figure 2.12 Crypto ACLs
88
How IPSec WorksStep 2

• IKE Phase 1
• Negotiate IKE policy sets (encryption type, hash
  algorithm, authentication method, key exchange,
  IKE Security Association Lifetime)
• Main mode or aggressive mode
• Main mode (default)
• Main mode has three bidirectional (two-way)
  exchanges between the initiator and the receiver.
• Aggressive mode
• Only three messages are exchanged
• Policies must match on both ends of the tunnel

89
How IPSec WorksStep 2 (cont.)

• First exchange The algorithms and hashes used to
  secure the IKE communications are agreed upon in
  matching IKE SAs in each peer.
•  
• Second exchange Uses a Diffie-Hellman exchange
  to generate shared secret keying material used to
  generate shared secret keys and to pass
  noncesrandom numbers sent to the other party and
  then signed and returned to prove their identity.
•  

90
How IPSec WorksStep 2 (cont.)

• Third exchange Verifies the other side's
  identity.
• The main outcome of main mode is matching IKE SAs
  between peers. The IKE SA specifies values for
  the IKE exchange the authentication method used,
  the encryption and hash algorithms, the
  Diffie-Hellman group used, the lifetime of the
  IKE SA in seconds or kilobytes, and the shared
  secret key values for the encryption algorithms.
  The IKE SA in each peer is bi-directional.

91
How IPSec WorksStep 2 (cont.)

• In aggressive mode, fewer exchanges are made
• On the first exchange, almost everything is
  squeezed into the proposed IKE SA values
• The receiver sends everything back that is needed
  to complete the exchange.
• The only thing left is for the initiator to
  confirm the exchange.
• The weakness of using the aggressive mode is
  that both sides have exchanged information before
  there's a secure channel. Therefore, it's
  possible to "sniff" the wire and discover who
  formed the new SA. However, it is faster than
  main mode.

92
How IPSec WorksStep 3

• IKE Phase 2
• Negotiate IPSec parameters (transform set, peers,
  traffic to be encrypted)
• IPSec parameters must match on both ends of the
  tunnel

93
How IPSec WorksStep 3 (cont.)

• IKE Phase 2 has one mode of operation, Quick
  mode, which begins immediately after the secured
  tunnel is established in IKE Phase 1
• The following tasks are accomplished during IKE
• IPSec SA parameters are negotiated and agreed on
  by both peers within the protection of the IKE SA
  established in Phase 1
• IPSec SAs are established
• IPSec SAs are renegotiated periodically as needed
• IPSec SAs an optionally perform an additional
  Diffie-Hellman key exchange

94
How IPSec WorksStep 4

• Once the IPSec SAs have been established in Step
  3, secured traffic can be exchanged over the
  connection
• Data Transfer
• Traffic is encrypted and decrypted according to
  parameters set in IKE phase 1 and IKE phase 2

95
How IPSec WorksStep 5

• IPSec tunnel termination
• SA timer expires
• If packet counter is exceeded
• In normal operation, IPSec VPN tunnels can be
  terminated two ways
• One of the peers goes away (deletion)
• More frequently, however, they out based on the
  negotiated SA lifetimes (timeouts)

96
Lecture 2 - Summary

• Understand Virtual Private Network Technologies
• List who benefits from VPNs
• List primary reasons for VPNs and typical
  applications of VPNs
• List 3 VPN benefits
• Identify 3 basic VPN categories
• List 4 Cisco VPN products
• Describe Management Software
• Recognize IPSec protocols and protocol framework
• Define 2 VPN Modes of Operation

97
Lecture 2 Summary (cont.)

• Describe Security Associations (SA)
• Define Message Encryption and Message Integrity
  (HMAC)
• List 3 Peer Authentication methods
• Define Key Management
• Identify the Key Exchange of Choice
  Diffie-Hellman
• Recognize Certificate Authorities (CAs)
• Authenticate IPSec Peers Form Security
  Associations
• List the 5 step process on how IPSec works

98
Lecture 2 - Labs

• Lab 1a Basic Host to Site VPN using PPTP
• Lab1b Basic Host to Site VPN using L2TP