Application Layer Protocols

  • Applications are running either as stand alone daemons: Apache, SSH, Sendmail, Samba, BIND, DHCP...
  • or started through application servers such as inetd or xinetd: telnet, rsh, rlogin, ftp, imap, pop3 ...

    Entry for FTP services in /etc/inetd.conf 
    ftp       stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/in.ftpd

  • The fields of /etc/inetd.conf contain the following:

    1. service-name valid name from /etc/services
    2. socket type stream for TCP and dgram for UDP
    3. protocol valid protocol from /etc/protocols
    4. flag nowait if multithreaded and wait if single-threaded
    5. user/group run application as user or group
    6. program usually tcpd
    7. argument the name of the daemon that needs to be run

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