D-Link DFL-260-IPS-12 Product Manual - Page 240
ALGs, 6.2.1. Overview, Deploying an ALG
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6.2. ALGs Chapter 6. Security Mechanisms 6.2. ALGs 6.2.1. Overview To complement low-level packet filtering, which only inspects packet headers in protocols such as IP, TCP, UDP, and ICMP, NetDefend Firewalls provide Application Layer Gateways (ALGs) which provide filtering at the higher application OSI level. An ALG object acts as a mediator in accessing commonly used Internet applications outside the protected network, for example web access, file transfer and multimedia transfer. ALGs provide higher security than packet filtering since they are capable of scrutinizing all traffic for a specific protocol and perform checks at the higher levels of the TCP/IP stack. ALGs exist for the following protocols in NetDefendOS: • HTTP • FTP • TFTP • SMTP • POP3 • SIP • H.323 • TLS Deploying an ALG Once a new ALG object is defined by the administrator, it is brought into use by first associating it with a Service object and then associating that service with an IP rule in the NetDefendOS IP rule set. Figure 6.1. Deploying an ALG 240
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