Security is an important issue in IP over satellite, since an attacker can easily intercept such communication and can even corrupt the transmitted data. In the first part of the paper, the authors address the implications of optimizing the Transport Control Protocol (TCP) on the security services provided by IPSec protocol suite. They provide a set of rules for optimizing TCP without interfering with IPsec. In the second part of the paper, they address IP multicast security issues. They also introduce an efficient key distribution algorithm that can handle a large dynamic group.