| You've already seen just about all the files containing network configuration information you're ever likely to need to work with. However, a few more files are still worth listing and briefly describing. This doesn't count config files for major network services, though; we'll cover those in Chapter 26, "Configuring a Web Server," and Chapter 32. Most of these files have man pages; simply use man filename, without the path, to view them (for example, man inetd.conf). Here's a description of the files: /etc/networks As you've already seen, this file contains symbolic names for subnets that you might want to use in places such as the routing table. /etc/hosts.allow This is a listing of fairly complex security rules for responding to connections of various types on a per-host basis. You can use hosts.allow to reject connections from certain hostswhether on a particular service or on all servicesor to specify an action to take when such a connection attempt is made. This mechanism only works for services that honor the hosts.allow file; third-party software packages such as Apache tend to use their own host management rules. /etc/inetd.conf The inetd "super-server" is responsible for accepting connection requests for services specified in inetd.conf and spawning a process to handle each one. Services run from within inetd include Telnet, FTP, POP3, and various miscellaneous services that you may want to disable if they're not needed. More on this in Chapter 30, "Network Security." /etc/services A database of IP service types and the TCP and UDP ports each maps to. Some programs use this table to look up commonly used ports; it also provides a handy reference for what services are assigned what ports by the Internet Assigned Numbers Authority (IANA). /etc/protocols Like /etc/services, this is a table providing keyword mappings for various IP subprotocol numbers. It is mostly of interest as a reference. /etc/rpc Another table of mappings, even less likely to be of interest to the administrator. RPC lookups provide port-mapping services to requests such as NFS, NIS, and various status-reporting programs. /etc/pam.d Pluggable Authentication Modules (PAM) provide a way to assign cascading authenticators (S/Key, Kerberos, and the like) to various services. This will be of interest when we discuss network security in Chapter 30. /etc/host.conf If present, this file specifies the order in which name lookup sources are given priority. In the default configuration, /etc/hosts is consulted first, followed by the resolver in BIND (the DNS running on the local machine). This file is automatically generated and should not require any manual editing.
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