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Section 1: UDP, TCP, and addresses

CSE 461. Section 1: UDP, TCP, and addresses. 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?. Getting own IP address: hostname method. Steps. Python example. Get the computer’s host name

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Section 1: UDP, TCP, and addresses

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

  2. Addressing • Project 0 requires sending your ownIP address to another client • Problem: getting own IP addresscan 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 • Get socket address import socket s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.connect((‘gmail.com’,80)) ip = s.getsockname()[0] • 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 toapplications/serviceson a system • 16-bit numbers (from0 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

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