ecure remote administration of various things.
IPSEC is not end-to-end
IPSEC cannot provide the same end-to-end security as systems working at higher levels. IPSEC encrypts an IP connection between two machines, which is quite a different thing than encrypting messages between users or between applications.
For example, if you need mail encrypted from the senders desktop to the recipients desktop and decryptable only by the recipient, use PGP or another such system. IPSEC can encrypt any or all of the links involved -- between the two mail servers, or between either server and its clients. It could even be used to secure a direct IP link from the senders desktop machine to the recipients, cutting out any sort of network snoop. What it cannot ensure is end-to-end user-to-user security. If only IPSEC is used to secure mail, then anyone with appropriate privileges on any machine where that mail is stored (at either end or on any store-and-forward servers in the path) can read it.
In another common setup, IPSEC encrypts packets at a security gateway machine as they leave the senders site and decrypts them on arrival at the gateway to the recipients site. This does not even come close to providing an end-to-end service. In particular, anyone with appropriate privileges on either sites LAN can intercept the message in unencrypted form.
IPSEC cannot do everything
IPSEC also cannot provide all the functions of systems working at higher levels of the protocol stack. If you need a document electronically signed by a particular person, then you need his or her digital signature and a public key cryptosystem to verify it with.
Note, however, that IPSEC authentication of the underlying communication can make various attacks on higher-level protocols more difficult. In particular, authentication prevents man-in-the-middle attacks.
IPSEC authenticates machines, not users
IPSEC uses strong authentication mechanisms to control which messages go to which machines, but it does not have the concept of user ID, which is vital to many other security mechansims and policies. This means some care must be taken in fitting the various security mechansims on a network together. For example, if you need to control which users access your database server, you need some non-IPSEC mechansim for that. IPSEC can control which machines connect to the server, and can ensure that data transfer to those machines is done securely, but that is all. Either the machines themselves must control user access or there must be some form of user authentication to the database, independent of IPSEC.
IPSEC does not stop denial of service attacks
Denial of service attacks aim at causing a system to crash, overload, or become confused so that legitimate users cannot get whatever services the system is supposed to provide. These are quite different from attacks in which the attacker seeks either to use the service himself or to subvert the service into delivering incorrect results.
IPSEC shifts the ground for DoS attacks; the attacks possible against systems using IPSEC are different than those that might be used against other systems. It does not, however, eliminate the possibility of such attacks.
IPSEC does not stop traffic analysis
Traffic analysis is the attempt to derive intelligence from messages without regard for their contents. In the case of IPSEC, it would mean analysis based on things visible in the unencrypted headers of encrypted packets -- source and destination gateway addresses, packet size, et cetera. Given the resources to acqui |