1. Network Services CSCI N321 – System and Network Administration Copyright © 2000, 2007 by Scott Orr and the Trustees of Indiana University

2. Section Overview Client-Server Model Network Ports, Services and Daemons Network Protocols Viewing Active Ports Common Server Daemons

3. References Linux System Administration Chapter 18 (pgs. 305-332) Optional: Chapters 20 & 21 CQU 85321 System Administration Course Textbook  Chapter 16 Chapter 16 Lectures  2002 #16 2002 #16

4. TCP/IP Protocol Stack Physical Layer (media) Link Layer (Device Drivers) Network Layer (IP) Transport Layer (TCP,UDP) Application (FTP, HTTP, DNS)

5. Client-Server Model Server Client Listens for incomingrequests Makes a request Request fulfilled

6. 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

7. Service-name port/protocol aliases Examples: ssh22/tcp smtp25/tcpmail www80/tcphttp www-http imaps993/tcp syslog514/udp

8. 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

9. 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

10. Xinetd Replacement for inetd Enhancements Access Control Resource based limits Logging (Success and Failure) Default: /etc/xinetd.conf Service Specific: /etc/xinetd.d

11. /etc/xinetd.conf defaults{ instances = 60 instances = 60 log_type = SYSLOG authpriv log_type = SYSLOG authpriv log_on_success = HOST PID log_on_success = HOST PID log_on_failure = HOST log_on_failure = HOST cps = 25 30 cps = 25 30} includedir /etc/xinetd.d

12. Example xinetd service /etc/xinetd.d/imaps: service imaps { disable = no disable = no socket_type = stream socket_type = stream wait = no wait = no user = root user = root server = /usr/local/sbin/imapd server = /usr/local/sbin/imapd groups = yes groups = yes flags = REUSE IPv6 flags = REUSE IPv6}

13. 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

14. 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

15. 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)

16. 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

17. Resource Sharing Daemons Network File System (NFS) nfsd mountd Line Printing Daemon ( lpd ) Samba smbd – Microsoft file and print sharing nmbd – Microsoft name resolution

18. 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

19. Infrastructure Daemons named – DNS dhcpd – Dynamic Host Config Protocol nisd/ldapd – Directory Services fingerd – User information xntpd – System time synchronization routed / gated – Routing Firewall