Networks and the Internet

It’s dangerous to go alone!

The internet is between you and a server.

137.112.146.189(Charles)

The Internet

208.80.152.201Wikipedia

DNS

Wikipedia server

Rose’s server

The DNS server• I want to say hi to wikipedia.org. • I ask my dns server:

• What is the address of wikipedia.org?• Tell 137.112.146.189

• The DNS server gets my packet, and looks up “wikipedia.org”– It finds an entry in its log:• Wikipedia.org ->208.80.152.201

• The DNS server tells me• Wikipedia.org is 208.80.152.201

Crafting a packet.

• I want to ask wikipedia for its main page. That is, tell wikipedia’s server to– Get /main_page.html, send it to me.

• I craft a packet:– Tell 208.80.152.201• Get /main_page.html• Send it to 137.112.146.189

• I release that packet to the internet.

Rose

Wikipedia

traceroute wikipedia.orgtraceroute to wikipedia.org (208.80.152.201), 30 hops max, 60 byte packets1 137.112.146.1 (137.112.146.1) 3.968 ms // Skinner switch2 137.112.9.35 (137.112.9.35) 0.566 ms //Rose’s router.3 ip-64-184-0-181.indianafiber.net (64.184.0.181) 3.297 ms //Rose-internet4 xe-10-3-0.bar2.Cincinnati1.Level3.net (4.59.42.17) 5.361 ms 5 ae-7-7.ebr2.Atlanta2.Level3.net (4.69.136.218) 18.507 ms6 ae-2-2.ebr2.Miami1.Level3.net (4.69.140.141) 31.373 ms7 ae-1-100.ebr1.Miami1.Level3.net (4.69.151.253) 30.734 ms8 ae-3-5.bar1.Tampa1.Level3.net (4.69.148.214) 36.790 ms9 ae-5-5.car1.Tampa1.Level3.net (4.69.133.13) 36.164 ms10 ae-13-13.car3.Tampa1.Level3.net (4.69.133.18) 36.536 ms11 level3.co1.as30217.net (4.71.0.14) 36.482 ms12 te3-4.co2.as30217.net (84.40.24.50) 40.225 ms //Wikipedia-internet13 10ge5-1.csw5-pmtpa.wikimedia.org (84.40.25.102) 42.481 ms //Wikipedia router.14 wikipedia-lb.pmtpa.wikimedia.org (208.80.152.201) 36.569 ms //Wikipedia server

Theinternet

Asia Pacific - RedUnknown - WhiteNorth America - BlueRFC1918 IP Addresses - CyanLatin American and Caribbean - YellowEurope/Middle East/Central Asia/Africa - Green

Date: Nov 22 2003 http://www.opte.org/maps/

Wikipedia gets my packet.

• Wikipedia’s server gets my packet. • It reads my request, and crafts a return packet:– Tell 137.112.146.189• The content of /main_page.html is:

• It sends that packet to the internet.• The internet gives me that packet.

The internet doesn’t always work.

• The internet is like the postal service. – It tries to get your packets to their destination as

fast as possible. – If one server is down, it can use another.

• It also has some bad things.– Someone can sniff your packets. Securing their

contents is your job. – Packets are guaranteed to arrive at least zero

times.

A discussion with Wikipedia

• Loading Wikipedia’s welcome page is a conversation of nearly 200 packets.

• DNS resolution: 6 packets.• Saying “Hi” to Wikipedia: 9 packets.• Wikipedia saying “Hi” back: 1 packet.• Me telling Wikipedia I heard it say hi: 1 packet.• Me requesting the front page: 1 packet• Both sides agreeing on sending content: 20 packets• Data transmission (and acknowledgement): 150 packets.

Server-side view192.168.1.100 - - [01/Jan/2012:18:51:47 -0500] "GET / HTTP/1.0" 200 44127.0.0.1 - - [01/Jan/2012:19:04:40 -0500] "GET / HTTP/1.0" 200 44127.0.0.1 - - [01/Jan/2012:19:05:37 -0500] "GET / HTTP/1.0" 200 44192.168.1.100 - - [01/Jan/2012:19:06:24 -0500] "GET / HTTP/1.0" 200 44192.168.1.100 - - [01/Jan/2012:19:08:54 -0500] "GET /.htaccess HTTP/1.0" 403 211192.168.1.100 - - [01/Jan/2012:19:09:13 -0500] "GET /hmm HTTP/1.0" 404 201192.168.1.100 - - [01/Jan/2012:19:10:15 -0500] "GET / HTTP/1.0" 200 52137.112.120.201 - - [02/Jan/2012:22:20:11 -0500] "GET / HTTP/1.1" 200 52137.112.120.201 - - [02/Jan/2012:22:20:11 -0500] "GET /favicon.ico HTTP/1.1" 404 209137.112.146.135 - - [02/Jan/2012:23:07:30 -0500] "GET / HTTP/1.1" 200 52137.112.146.135 - - [02/Jan/2012:23:07:30 -0500] "GET /favicon.ico HTTP/1.1" 404 209114.205.1.94 - - [02/Jan/2012:23:22:59 -0500] "GET /vhosts/ehcp/?op=applyfordomainaccount HTTP/1.1" 404 210114.205.1.94 - - [02/Jan/2012:23:23:00 -0500] "GET /ehcp/?op=applyfordomainaccount HTTP/1.1" 404 203137.112.146.135 - - [03/Jan/2012:01:52:38 -0500] "GET /favicon.ico HTTP/1.1" 404 209//Here, I blocked access to the server to everyone. 137.112.146.135 - - [03/Jan/2012:01:53:19 -0500] "GET / HTTP/1.1" 403 202137.112.146.135 - - [03/Jan/2012:01:53:19 -0500] "GET /favicon.ico HTTP/1.1" 403 213137.112.146.135 - - [03/Jan/2012:01:53:20 -0500] "GET / HTTP/1.1" 403 202137.112.146.135 - - [03/Jan/2012:01:53:20 -0500] "GET /favicon.ico HTTP/1.1" 403 213208.25.216.194 - - [03/Jan/2012:12:15:13 -0500] "HEAD / HTTP/1.0" 403 -107.22.72.52 - - [03/Jan/2012:13:25:27 -0500] "HEAD / HTTP/1.0" 403 -81.201.60.168 - - [03/Jan/2012:22:57:00 -0500] "GET / HTTP/1.0" 403 202

1xx codes:InformationalUncommon.

2x codes:Success200: OK

3xx codes:Redirect301: permanent304: not modified

4xxClient error403: forbidden404: not found

5xx:Server error500: server broken501: not implemented503: server down

Credits

• Map of IPv4 address space: http://xkcd.com/195/

• Level3 network: http://www.hcwt.com/level3.php?search_what=level3

• Internet map http://opte.org/maps/