Dell Brocade G620 Brocade 8.0.1 Fabric OS Administratiors Guide - Page 250

Configuring Security Policies IPsec protocols protect IP datagram integrity using hash message authentication codes (HMAC). Using hash algorithms with the contents of the IP datagram and a secret key, the IPsec protocols generate this HMAC and add it to the protocol header. The receiver must have access to the secret key in order to decode the hash. IPsec protocols use a sliding window to assist in flow control, The IPsec protocols also use this sliding window to provide protection against replay attacks in which an attacker attempts a denial of service attack by replaying an old sequence of packets. IPsec protocols assign a sequence number to each packet. The recipient accepts each packet only if its sequence number is within the window. It discards older packets. Security associations A security association (SA) is the collection of security parameters and authenticated keys that are negotiated between IPsec peers to protect the IP datagram. A security association database (SADB) is used to store these SAs. Information in these SAs--IP addresses, secret keys, algorithms, and so on--is used by peers to encapsulate and decapsulate the IPsec packets An IPsec security association is a construct that specifies security properties that are recognized by communicating hosts. The properties of the SA are the security protocol (AH or ESP), destination IP address, and Security Parameter Index (SPI) number. SPI is an arbitrary 32-bit value contained in IPsec protocol headers (AH or ESP) and an IPsec SA is unidirectional. Because most communication is peer-to-peer or client-to-server, two SAs must be present to secure traffic in both directions. An SA specifies the IPsec protocol (AH or ESP), the algorithms used for encryption and authentication, and the expiration definitions used in security associations of the traffic. IKE uses these values in negotiations to create IPsec SAs. You must create an SA prior to creating an SA-proposal. You cannot modify an SA once it is created. Use the ipSecConfig --flush manual-sa command to remove all SA entries from the kernel SADB and recreate the SA. IPsec proposal The IPsec sa-proposal defines an SA or an SA bundle. An SA is a set of parameters that define how the traffic is protected using IPsec. These are the IPsec protocols to use for an SA, either AH or ESP, and the encryption and authentication algorithms to use to protect the traffic. For SA bundles, [AH, ESP] is the supported combination. Authentication and encryption algorithms IPsec uses different protocols to ensure the authentication, integrity, and confidentiality of the communication. Encapsulating Security Payload (ESP) provides confidentiality, data integrity and data source authentication of IP packets, and protection against replay attacks. Authentication Header (AH) provides data integrity, data source authentication, and protection against replay attacks, but unlike ESP, AH does not provide confidentiality. In AH and ESP, hmac_md5 and hmac_sha1 are used as authentication algorithms. Only in ESP, 3des_cbc, blowfish_cbc, aes256_cbc and null_enc are used as encryption algorithms. Use Table 55 when configuring the authentication algorithm. TABLE 55 Algorithms and associated authentication policies Algorithm Encryption Level hmac_md5 128-bit hmac_sha1 160-bit Policy AH, ESP AH, ESP Description A stronger MAC because it is a keyed hash inside a keyed hash. When MD5 or SHA-1 is used in the calculation of an HMAC; the resulting MAC algorithm is termed HMAC-MD5 or HMAC-SHA-1 accordingly. 250 Brocade Fabric OS Administration Guide, 8.0.1 53-1004111-02