the firewall.
at the network layer, or, at most, the transport layer. This allows support of protocols that
involve multiple channels created as a result of negotiations in the control channel. Most of the
multimedia protocols as well as some other protocols (such as FTP, RPC, and SQL*Net)
involve multiple channels. For example, FTP uses ports 20 and 21, one port for control and one
port for data, as shown in Figure 15-12.
overview and discusses some of the basic mechanisms utilized with IPSec. IPSec works at the
network layer. It is a set of protocols and algorithms that work together to secure data between
endpoints. IPSec consists of two authentication protocols, Encapsulation Security Payload
(ESP) and Authentication Header (AH), and two protection modes, tunnel and transport. Public
and private encryption keys are also discussed, including the Diffie-Hellman method of key
exchange. CCDPs need to know the basic mechanics of IPSec and its advantages and
disadvantages in large enterprise networks.
the data but does not manipulate the addressing portion of the packet. It leaves the header alone,
so it does not provide for data origin authentication. What ESP does is scramble the data in the
packet so that if the packet is intercepted, the attacker cannot get the information in the packet.
ESP can be in two modes--transport or tunnel. Transport mode is used within a network where