2.1.8. Native services

Native services provide a limited number of server-like features in PNS. Their use is optional and depends on the needs and security requirements of your organization. The use of Network Time Protocol (NTP) and Bind is recommended, while Postfix is useful for managing mail traffic from various firewall components locally.

These services are called native because they are installed with PNS and are available by default. They are implementations of the actual Linux services of the same names. These services provide networking services that are either difficult to implement with application proxies (or at the packet filter level) or provide services for the firewall itself. For more information on these services, see Chapter 9, Native services.

  • NTP: PNS hosts can function both as a Network Time Protocol (NTP) client and server. Time synchronization among the PNS hosts is very important for correct logging entries. Once the firewall's time is correctly synchronized, it can act as the authentic time source for its internal networks.

  • DNS: PNS features a fully functional ISC BIND 9 DNS server. It is optional and definitely not mandatory to use if security regulations explicitly prohibit the installation of non-firewall software on the firewall machine. However, in small and mid-sized networks, it can be beneficial to have a built-in name server, if it is solely used as a forward–only DNS server.

  • SMTP: PNS uses Postfix as the built-in SMTP server component. Postfix is used for SMTP queuing. PNS also has an application proxy for inspecting SMTP traffic, while CF can be used to perform virus, spam, and content-based filtering on the SMTP traffic. The primary role of this Postfix service is to provide a Mail Transport Agent (MTA) for the firewall itself: a number of mail messages can originate from the firewall, and these messages are delivered using the Postfix service. Although the Postfix service is a fully functional MTA in PNS, it is not intended to be a general purpose mail server solution for any organization.

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