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Configuration of a Site-to-Site IPsec Virtual Private Network Anuradha Kallury CS 580 Special Project August 23, 2005

Configuration of a Site-to-Site IPsec Virtual Private Network Anuradha Kallury CS 580 Special Project August 23, 2005. IPsec – An Introduction. IPsec is a suite of protocols used to create virtual private networks (VPNs) Creates encrypted tunnel between 2 private networks

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Configuration of a Site-to-Site IPsec Virtual Private Network Anuradha Kallury CS 580 Special Project August 23, 2005

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  1. Configuration of a Site-to-Site IPsec Virtual Private Network Anuradha Kallury CS 580 Special Project August 23, 2005

  2. IPsec – An Introduction • IPsec is a suite of protocols used to create virtual private networks (VPNs) • Creates encrypted tunnel between 2 private networks • Authenticates both ends of the tunnel

  3. IPsec – An Introduction (Cont’d) • Can choose what traffic to encrypt and how to encrypt it • Encapsulates and encrypts IP data only (can use GRE for non-IP traffic) • IPsec is composed of the following main protocols: • Internet Key Exchange (IKE) protocol • Encapsulating Security Payload (ESP) protocol • Authentication Header (AH) protocol

  4. IPsec - Fundamental Mechanisms • Packet Encapsulation • Encapsulating Security Payload (ESP) - encrypts and authenticates data • Authentication Header (AH) – authenticates data and header • Tunnel mode - new IP header appended in front of original IP header of packet • Transport mode - uses original IP header of packet • Encryption • Uses symmetric key algorithms DES or 3DES • Integrity Checking • Uses Message Authentication Codes using Hashing (HMAC) • Hashing algorithms used are MD5 or SHA-1

  5. IPsec Implementation • LAN-to-LAN IPsec VPN • Also called site-to-site IPsec VPN • Merges 2 private networks across a public network • Appears as one virtual network with shared resources

  6. IKE – An Introduction • Responsible for negotiating the details of the IPsec tunnel between the 2 peers • Main functions of IKE in IPsec: • Negotiate protocol parameters • Exchanging public keys • Authenticate both ends • Managing keys after exchange

  7. How IKE Works • IKE is a two phase protocol • Phase 1 • Uses main mode or aggressive mode exchanges between peers • Negotiates a secure, authenticated communication channel between the IPsec peers • Phase 2 • Uses quick mode exchanges between peers • Negotiates security associations for the IPsec services

  8. IKE - Main Mode • The main functions of the main mode (or aggressive mode) are: • Agree on a set of parameters that will be used to authenticate the 2 IPsec peers • Agree on a set of parameters that will be used to encrypt a part of the main mode and all of the quick mode exchange. • Authenticate the 2 IPsec peers to each other • Generate keys that can be used to generate the necessary data encryption keys after negotiations are done.

  9. IKE - Main Mode (Cont’d) • All the information negotiated in main mode is stored as an IKE or ISAKMP security association (SA). • There is only one SA between any 2 IPsec peers.

  10. IKE - Quick Mode • The main functions of the quick mode are: • Agree on a set of parameters for creating the IPsec SAs used to encrypt (for ESP) the data between the 2 peers • If Perfect Forward Secrecy (FPS) is being used, performs another Diffie-Hellman (DH) exchange to generate new keys for generating the data encryption keys

  11. IKE Authentication Mechanisms • Preshared Keys • Define the same key on both IPsec peers • Simple but not scalable • Digital Signatures • Uses public/private key pairs generated on both IPsec peers • Public key is exchanged using a digital certificate that also contains sender info • Certificate issued by a certificate authority (CA) server • Encrypted Nonces • Pseudo-random numbers are encrypted and exchanged by the IPsec peers

  12. IPsec Negotiation Using IKE • IKE negotiates IPsec tunnels between IPsec peers using one of three main methods: • Main mode using preshared key authentication followed by quick mode negotiation • Main mode using digital signature authentication followed by quick mode negotiation • Aggressive mode using preshared key authentication followed by quick mode negotiation

  13. Configuration of LAN-to-LAN IPsec - Network Diagram Responder Initiator 192.1.12.5 192.1.12.20 10.1.2.0/24 10.1.1.0/24 • Cisco Routers R1 and R2 both running IOS version 12.2.15T11 (including support for IPsec and 3DES) • Cisco Catalyst Switch 3550-01 running IOS version 12.1.22(EA1a)

  14. priority Configuration of LAN-to-LAN IPsec - Setup of Routers • Step 1: Ensure that IKE is enabled Router(config)# crypto isakmp enable • Step 2: Create the ISAKMP policy which defines the attributes negotiated between the peers for the IKE SA Router(config)# crypto isakmp policy 1 Router(config-isakmp)# encryption 3des Router(config-isakmp)# hash md5 Router(config-isakmp)# authentication pre-share Router(config-isakmp)# group 1 Router(config-isakmp)# lifetime 14400

  15. Configuration of LAN-to-LAN IPsec - Setup of Routers (Cont’d) • Step 3: Define the pre-shared key and the IP address of the IPsec peer Router(config)# crypto isakmp key 42DB72B3 address 192.1.12.20 • Step 4: Define a transform-set for use with IPsec as follows: Router(config)# crypto ipsec transform-set myset1 esp-3des esp-md5-hmac • Step 5: Define the mode associated with the transform-set (optional) Router(cfg-crypto-tran)# mode tunnel

  16. Configuration of LAN-to-LAN IPsec - Setup of Routers (Cont’d) • Step 6: Define an access list which specifies the interesting traffic for IPsec • Can be used to specify “interesting” traffic for IPsec Router(config)# access-list 101 permit ip 10.1.1.0 0.0.0.255 10.1.2.0 0.0.0.255 • Step 7: Define a crypto map • The crypto map links together all of the details of the IPsec configuration Router(config)# crypto map mymap1 ipsec-isakmp

  17. Configuration of LAN-to-LAN IPsec - Setup of Routers (Cont’d) • Step 8: Within the identified crypto map, define the IP address of the IPsec peer Router(config-crypto-m)# set peer 192.1.12.20 • Step 9: Within the identified crypto map, define which transform-set is to be used with this crypto map Router(config-crypto-m)# set transform-set myset1 • Step 10: Within the identified crypto map, define which access list is to be used with this crypto map Router(config-crypto-m)# match address access-list 101

  18. Configuration of LAN-to-LAN IPsec - Setup of Routers (Cont’d) • Step 11: Assign the crypto map to the specific interface of the router on which IPsec traffic will flow Router(config)# interface Ethernet 0/0 Router(config-if)# crypto map mymap1 • Step 12: Verify that the defined policy, transform-set, and pre-shared key are the same on both IPsec peers

  19. Configuration of LAN-to-LAN IPsec – Viewing IPsec attributes • Assigned IPsec attributes can be viewed using following commands: Router# show crypto isakmp policy Router# show crypto isakmp sa Router# show crypto isakmp key Router# show crypto ipsec transform-set Router# show crypto map Router# show crypto ipsec sa Router# show crypto ipsec security-association lifetime

  20. Configuration of LAN-to-LAN IPsec – Screenshot1 of Router 1 crypto

  21. Configuration of LAN-to-LAN IPsec – Screenshot2 of Router 1 crypto

  22. Configuration of LAN-to-LAN IPsec – Screenshot1 of Router 1 config

  23. Configuration of LAN-to-LAN IPsec – Screenshot2 of Router 1 config

  24. Configuration of LAN-to-LAN IPsec – Screenshot3 of Router 1 config

  25. Configuration of LAN-to-LAN IPsec – Screenshot1 of Router 2 crypto

  26. Configuration of LAN-to-LAN IPsec – Screenshot2 of Router 2 crypto

  27. Configuration of LAN-to-LAN IPsec – Screenshot1 of Router 2 config

  28. Configuration of LAN-to-LAN IPsec – Screenshot2 of Router 2 config

  29. Configuration of LAN-to-LAN IPsec – Screenshot3 of Router 2 config

  30. Configuration of LAN-to-LAN IPsec Debug output on router 1 (initiator)

  31. Configuration of LAN-to-LAN IPsec Debug output on router 1 (cont’d)

  32. Configuration of LAN-to-LAN IPsec Debug output on router 1 (cont’d)

  33. Configuration of LAN-to-LAN IPsec Debug output on router 1 (cont’d)

  34. Configuration of LAN-to-LAN IPsec Debug output on router 1 (cont’d)

  35. Configuration of LAN-to-LAN IPsec Debug output on router 1 (cont’d)

  36. Configuration of LAN-to-LAN IPsec Debug output on router 2 (responder)

  37. Configuration of LAN-to-LAN IPsec Debug output on router 2 (cont’d)

  38. Configuration of LAN-to-LAN IPsec Debug output on router 2 (cont’d)

  39. References • Network Security Principles and Practices by Saadat Malik • Cisco IOS Security Configuration Guide, Release 12.2 • Cisco IOS Security Command Reference, Release 12.2 • Cisco IOS Configuration Fundamental Configuration Guide, Release 12.2 • Cisco IOS Interface Command Reference, Release 12.2

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