Network Services
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Network Services

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Network Services Network Services Presentation Transcript

  • Network Services CSCI N321 – System and Network Administration Copyright © 2000, 2007 by Scott Orr and the Trustees of Indiana University
  • Section Overview
    • Client-Server Model
    • Network Ports, Services and Daemons
    • Network Protocols
    • Viewing Active Ports
    • Common Server Daemons
  • References
    • Linux System Administration
        • Chapter 18 (pgs. 305-332)
        • Optional: Chapters 20 & 21
    • CQU 85321 System Administration Course
    • Textbook
    • Chapter 16
    • Lectures
    • 2002 #16
    View slide
  • TCP/IP Protocol Stack Physical Layer (media) Link Layer (Device Drivers) Network Layer (IP) Transport Layer (TCP,UDP) Application (FTP, HTTP, DNS) View slide
  • Client-Server Model Server Client Listens for incoming requests Makes a request Request fulfilled
  • Network Ports
    • Enables processes to communicate with each other across a network
    • 64K possible ports
    • Privileged ports
      • < 1024 reserved for system use only
      • Correspond to well-known services
      • /etc/services
  • /etc/services
    • Service-name port/protocol aliases
    • Examples:
    • ssh 22/tcp
    • smtp 25/tcp mail
    • www 80/tcp http www-http
    • imaps 993/tcp
    • syslog 514/udp
  • Running Network Servers
    • Stand-alone Daemon
      • Each started via rc script
      • Always running
      • Listens (binds) to the service port
      • Uses resources even when idle
    • inetd “Super-daemon”
      • Listens to many ports
      • Starts daemon when request is received
      • Daemon shuts down when finished
      • /etc/inetd.conf
  • /etc/inetd.conf
    • service_name: Service name
    • sock_type:
      • stream (tcp)
      • dgram (udp)
      • raw (direct IP)
    • proto : protocol used ( /etc/protocol )
    • flags : wait, nowait
    • user : User to run daemon as
    • server_path : Full path to daemon program
    • args : Command line arguments to daemon
  • Xinetd
    • Replacement for inetd
    • Enhancements
      • Access Control
      • Resource based limits
      • Logging (Success and Failure)
    • Default: /etc/xinetd.conf
    • Service Specific: /etc/xinetd.d
  • /etc/xinetd.conf defaults { instances = 60 log_type = SYSLOG authpriv log_on_success = HOST PID log_on_failure = HOST cps = 25 30 } includedir /etc/xinetd.d
  • Example xinetd service /etc/xinetd.d/imaps: service imaps { disable = no socket_type = stream wait = no user = root server = /usr/local/sbin/imapd groups = yes flags = REUSE IPv6 }
  • Windows Service Management
    • Microkernel – Everything a service
    • Administrative tools -> Services
    • Service Options
      • Startup Type: Automatic, Manual, Disabled
      • Log On: Which user to run service as
      • Recovery: What to do on failure
      • Dependencies: Which services does this one depend upon
  • Windows Service Recovery
    • Settings for:
      • First Failure
      • Second Failure
      • Subsequent Failures
    • Counter Reset (Days)
    • Options:
      • Take no Action
      • Restart the Service
      • Run a program
      • Restart the Computer
  • Network Protocols
    • Service request/response syntax
    • Often uses English commands
    • Request For Comments (RFC)
      • Documentation for protocols and practices
      • Each revision its own number
      • May have a second classification
        • For Your Information (FYI)
        • Best Common Practices (BCP)
        • Standards (STD)
  • Viewing Active Ports
    • netstat –a – Ports in use
      • Source/destination addresses and ports
      • Protocol used
      • State
        • LISTEN
        • ESTABLISHED
    • lsof –i :service – Process using port
    • tcpdump – View network traffic
  • Resource Sharing Daemons
    • Network File System (NFS)
      • nfsd
      • mountd
    • Line Printing Daemon ( lpd )
    • Samba
      • smbd – Microsoft file and print sharing
      • nmbd – Microsoft name resolution
  • Internet Daemons
    • telnetd – Remote Access
    • ftpd – File transfer
    • Berkeley-R Daemons
    • sshd – Secure Shell
    • Electronic Mail
      • sendmail/postfix – Receiving email
      • imapd , popd – Remote email access
    • httpd – Web
  • Infrastructure Daemons
    • named – DNS
    • dhcpd – Dynamic Host Config Protocol
    • nisd/ldapd – Directory Services
    • fingerd – User information
    • xntpd – System time synchronization
    • routed / gated – Routing
    • Firewall