how HMAC works in IPSec

[Athul Chandran]

can somebody explain how HMAC works in IPSec? i know HMAC attaches secret key to HASH. But whats that secret key? and how it is created? and how it passes to another peer (responder)?

Why its required in IPSec?

Thanks

AC

[Frank DeNofa]

Athul,

In short, HMAC is the authentication/integrity part of IPsec encapsulation. It serves as a means of verifying that the packet you're receiving was actually sent by your peer and has not been modified in transit. This Cisco Press doc does a decent job at going into some additional detail: http://www.ciscopress.com/articles/article.asp?p=25473

HTH,

Frank