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  1. 1. IPSEC Protocols Encryption AlgorithmsInternet Security Association and Key Management Type Key Length (Bits) StrengthProtocol (ISAKMP) DES Symmetric 56 WeakA framework for the negotiation and management ofsecurity associations between peers (traverses UDP/500) 3DES Symmetric 168 MediumInternet Key Exchange (IKE) AES Symmetric 128/192/256 StrongResponsible for key agreement using asymmetric RSA Asymmetric 1024+ StrongcryptographyEncapsulating Security Payload (ESP) Hashing AlgorithmsProvides data encryption, data integrity, and peer Length (Bits) Strengthauthentication; IP protocol 50 MD5 128 MediumAuthentication Header (AH) SHA-1 160 StrongProvides data integrity and peer authentication, but not dataencryption; IP protocol 51 IKE Phases IPsec Modes Phase 1 A bidirectional ISAKMP SA is established Original between peers to provide a secure management L2 IP TCP/UDP Packet channel (IKE in main or aggressive mode)Transport Phase 1.5 (optional) L2 IP ESP/AH TCP/UDP Mode Xauth can optionally be implemented to enforce user authentication Tunnel L2 New IP ESP/AH IP TCP/UDP Phase 2 Mode Two unidirectional IPsec SAs are established forTransport Mode data transfer using separate keys (IKE quickThe ESP or AH header is inserted behind the IP header; the mode)IP header can be authenticated but not encrypted TerminologyTunnel ModeA new IP header is created in place of the original; this Data Integrityallows for encryption of the entire original packet Secure hashing (HMAC) is used to ensure data has not been altered in transit Configuration Data Confidentiality ISAKMP Policy Encryption is used to ensure data cannot becrypto isakmp policy 10 encryption aes 256 intercepted by a third party hash sha Data Origin Authentication authentication pre-share Authentication of the SA peer group 2 lifetime 3600 Anti-replay Sequence numbers are used to detect and ISAKMP Pre-Shared Key discard duplicate packetscrypto isakmp key 1 MySecretKey address Hash Message Authentication Code (HMAC) A hash of the data and secret key used to IPsec Transform Set provide message authenticitycrypto ipsec transform-set MyTS esp-aes 256 esp-sha-hmac mode tunnel Diffie-Hellman Exchange A shared secret key is established over an IPsec Profile insecure path using public and private keyscrypto ipsec profile MyProfile set transform-set MyTS Troubleshooting show crypto isakmp sainterface Tunnel0 Virtual Tunnel Interface ip address show crypto isakmp policy tunnel source tunnel destination show crypto ipsec sa tunnel mode ipsec ipv4 show crypto ipsec transform-set tunnel protection ipsec profile MyProfile debug crypto {isakmp | ipsec}by Jeremy Stretch v2.0