Linux Networking

1. Linux Networking CIS230.0325

2. Why Linux/Unix? • Configurability • Customizable System to satisfy unique needs. • Scalability • Able to serve an increasing number of users with out down time. • Stability • Exceptional design to avoid crashes

3. Daemon & HTTPD • Daemon • Linux Program • Runs in the background • Starts up and shuts down with the system • Httpd • D for daemon • Runs in the background • Answers server request from clients

4. Inetd & TCP Wrappers • Inetd • Links ports to associated server domain • Runs appropriate programs that are requested • TCP Wrappers • Grants or denies Server Request • Logs network use • Date • Time • Service requested • Clients name • Address

5. File Sharing • FTP (file transfer protocol) • NFS (network file system) • To access shared file: • file must be listed in the NFS server host file. • User must know location • Mount file using mount command (line prompt) • Able to view mounted file like directory

6. Network File System • NFS allows users to view/share files in Unix/Linux • Allows users to access their files from virtually any computer • Virtual file system • NFS Request are stateless • Repeats client request during system crash • During reboot, server would then answer request like the system crash never occurred • Knfsd – Kernel network file system daemon • Runs in Kernel mode • Uses NFS tools to improve response time for clients

7. Server Message Block • SMB is a client/server protocol • Application and presentation level protocol • Runs on transport and network protocols • In charge of • File sharing • Printing • Logins

8. Samba/Share • Samba is server for sharing, printing, and login services • Share allows users in a SMB to share resources in network • Two components of samba: • Smbd: responsible for file and print services and executes users verifications • Nmbd: applies name resolution and browsing

9. SWAT • Samba Web Administration Tool allows system administrator: • Change Samba configuration • Select shares • Set verification requirements like user name and password

10. Postscript/Ghostscript • Postscript: • Is used to optimize printing graphics and text • Provides convenient language for printing with out reference to any device features like printer resolution • Ghostscript converts postscript documents to raster • ( composed of pixels and dot) image. Because inkjet printers are not compatible with postscript Postscript is the Linux/Unix page description language.

11. LPD/CUPS LPD (line printer daemon) CUPS (common Unix printing system) • Linux Print Spooler • Starts when computer boots • Waits for print request from clients • Holds prints jobs until printer is ready • Prints the next file on the list • Allows computer to act as a print server • Accept print jobs from clients • Process and sends to appropriate printer • Consist of spooler, scheduler and filter system • Converts print data to a format that the printer understands

12. Internet Printing Protocol • IPP manages print jobs and queues • Runs on HTTP and allows bidirectional communication between server and client • Allows search for available printers in the network • Verifies which client can access server host • Stores logs and provides accounting capability • Offers compatibility with older LPD-style clients

13. Apache • Open source web server used by Linux/Unix • Powers more then half the web sites around the world (ex. hotmail, yahoo) • Displays and serves HTML pages hosted on a server to a client browser

14. KHTTPD • Kernel mode Linux daemon that provides a web service • Able to run on Apache • Kernel mode speeds up serving of static pages • Errors are able to bring down an entire system • User based process are more stable

15. Apache pre-forking • Creates multiple child processes to handle HTTP request • Parents process checks to see child process are working properly and coordinates everything • As more HTTP request are made, more child process are created to process them • When HTTP goes idle, the parent would kill child processes to free up resource • If child process were to crash, the parent and other child would not be effected • This process make apache very reliable

16. Apache - Modular Architecture • Provides basic http functionality and other modules to provide additional functionality • Supports dynamic shared object that permit loading of external modules at a run time • Provides Application Programming Interface (APT) • Apache is fully customizable to the administrator or programer • Portable run-time layer provides • File input/output • Network input/output • Own memory management routines

17. Apache Filter • Accepts input from the standard input device • modifies data and sends the results to the standard output device • Used internally to process internal functions • When receiving a request, it delegates the request to a single content handler module that sends the data back to the client

18. Clusters & Beowulf Clusters • Consist of multiple computers, each with its own O.S • Works with high speed network • Goals • High performance • High availability • Load balance • Scalability • Manageability Beowulf Clusters • Tightly connected network computers dedicated to the solution of a single problem • Links multiple inexpensive computers to achieve the performance of a super computer • Low priced

19. Single System Image • A SSI is a comprised of multiple resources such as • Networks • Distributed Databases • Or Servers • To act as a single unified powerful resource • Linked to form peer-to-peer network • Does not share client-server relationship • Managed by the operating system’s kernel • Unlike Beowulf clusters • Does not need to be modified to use MPI • Regular programs can run without modification • Doesn’t need to be cluster aware to have benefits

20. Cryptic line commands vs. User-friendly interface