Understanding IP Addressing, Ports, and Hostnames in Networking

Exploring methods to obtain own IP address, well-known ports, hostname resolution, and mapping hostnames to IP addresses in networking. Discover the significance of ports, addressing projects, and DNS servers in establishing communication protocols like UDP and TCP.

• IP Addressing
• Networking
• Ports
• Hostnames
• DNS Servers

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1. CSE 461 Section 1: UDP, TCP, and addresses

2. Addressing Project 0 requires sending your own IP address to another client Problem: getting own IP address can be hard How can we do it?

3. Getting own IP address: hostname method Steps Python example Get the computer s host name Resolve it into an IP address import socket name = socket.gethostname() ip = socket.gethostbyname(name) Sometimes doesn t work depending on hostname configuration and/or will just return local host (127.0.0.1)

4. Getting own IP address: connect to server method Steps Python example Create a socket Connect to known server on internet import socket s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.connect(( gmail.com ,80)) ip = s.getsockname()[0] Get socket address Useful when previous method doesn t work Similar methods exist for other languages as well

5. Other Methods getaddrinfo() E.g., socket.getaddrinfo(name, 0) Can return other network interfaces that you don t want (e.g., IPv6) Querying outside URL E.g., urllib2.urlopen( http://abstract.cs.washington.edu/~zahorjan/ip.cgi ).read() Best method (if you have a dedicated server to tell you your IP)

6. Ports Addresses specific to applications/services on a system 16-bit numbers (from 0 to 165535)

7. Well-Known Ports Many applications/services have designated ports Examples: ftp: 21 ssh: 22 telnet: 23 http: 80 Ports from 0 to 1023 are well-known ports (don t use them for protocols you make up!) Can see a list of your system s well known ports in /etc/services (Linux/Unix)

8. Hostnames map to IP addresses Hosts contact DNS (Domain Name System) servers to get IP address of a given name E.g., www.gmail.com maps to 173.194.33.118 nslookup demo