The document provides an overview of Internet Protocol (IP) addressing, including the concept of reliability in datagram delivery and the structure of IP addresses. It explains routing, subnetting, multicast versus unicast communication, and the use of the xinetd daemon for managing internet services in Linux. Key technical details such as routing protocols, multicast IP address ranges, and configuration files are also discussed.

1. Compiled by: Jayakumar Balasubramanian Web: http://www.jwritings.com Email: [email_address]

2. Introduction to IP The concept of ‘unreliability’ Datagram delivery from source to destination Creates a ‘virtual path’ and forms the basis of packet switching Takes the optimal/shortest path Learn the network topology and perform ‘routing’ functionality Independent of data link layer technology

3. Recap of addressing

4. The IP address Logical address 32 bit length IP address parts: Network part Host part Multiple classes Class A Class B Class C Special class The ‘heart’ of routing

5. Subnet mask The subnet mask is used to get the network portion of the IP address. This is basically achieved by performing logical AND. By looking into the subnet mask we can determine the class of the IP address. The concept of ‘subnetting’

6. Example

7. The concept of ‘routing’

8. Some more concepts Route types: Network specific route Host specific route Default route Type of protocols Routing protocols (Ex) OSPF, BGP Routed protocols (Ex) TCP, DNS, SNMP Data link layer Maximum Transfer Unit (MTU) Segmentation and re-assembly (SAR)

9. Special class of IP addresses Broadcast Address Multicast Address Loop back Address

10. The concept of Multicasting Have you used Yahoo/Google groups? Instead of sending a separate copy of the data for each recipient, the source ends the data only once. Unicast does mass mailings; Multicast does chain letters. Advantages: Cost-efficient Timely distribution of data Reduces WAN traffic

11. Multicast IP addresses The IP address belongs to ‘Class D’ Ranges from 224.0.0.0 to 239.255.255.255 Each address corresponds to a particular group/pre-defined protocol. 224.0.0.1 is for “All-hosts-in-LAN”

12. Sockets and multicasting options The ‘setsockopt’ API: setsockopt (int sockFd, int level, int optname, const void* optval, socklen_t optlen); level : IPPROTO_IP opt-name: IP_ADD_MEMBERSHIP IP_DROP_MEMBERSHIP

13. struct ip_mreq struct ip_mreq { struct in_addr imr_multiaddr; struct in_addr imr_interface; };

14. The ‘xinetd’ daemon The ‘xinetd’ is a replacement for ‘inetd’, the internet services daemon. Each internet services are categorized based on port number. The daemons in Linux are started when the system is booting up. Basically all standard servers (Telnet, FTP, SSH, etc..) are started in the similar way. Our idea is to make our server program as a daemon and try out some things.

15. Some basics The syntax of ‘select()’ and brush up. Standard socket descriptors: STDIN and STDOUT. Linux specific: The /etc directory The *.conf files in Linux

16. The /etc/services file Defines the sockets and protocols used for Internet services. Each service is listed on a single line corresponding to the form: Syntax: ServiceName PortNumber/ProtocolName Aliases ServiceName - Specifies an official Internet service PortNumber - Specifies the socket port number user ProtocolName - Specifies the transport protocol used Aliases - Specifies a list of unofficial service names.

17. Example echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null daytime 13/tcp daytime 13/udp chargen 19/tcp ttytst source chargen 19/udp ttytst source ftp 21/tcp time 37/tcp timeserver

18. The /etc/xinetd.conf file xinetd.conf is the configuration file that determines the services provided by xinetd . Any line whose first non-white-space character is a '#' is considered a comment line. Empty lines are ignored. Each entry defines a service identified by the service_name. This is where the service specific details are provided.

19. Syntax and Example service <service_name> { <attribute> <assign_op> <value> <value> ... ... } service SMTP { socket type = stream protocol = tcp wait = no user = mail server = /usr/sbin/exim }

20. Inside your program Important points: Use ‘select’ and STDIN combination for receiving client requests. Use STDOUT for sending the data out to clients. Restarting the ‘xinetd’ /etc/init.d/xinetd restart

21. Web : http://www.jwritings.com Email: [email_address]