RCSP Study Guide - IPSec
You configure IPSec encryption to allow data to be communicated securely between peer Steelhead appliances. Enabling IPSec encryption makes it difficult for a third party to view your data or pose as a machine you expect to receive data from.
To enable IPSec, you must specify at least one encryption (DES or NULL) and authentication algorithm (MD5 or SHA-1). Only optimized data is protected, passthrough traffic is not.