Networks and the Internet
It’s dangerous to go alone!
The internet is between you and a
server.
137.112.146.189
(Charles)
Rose’s
server
The Internet
Wikipedia
server
DNS
208.80.152.201
Wikipedia
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.org
traceroute to wikipedia.org (208.80.152.201), 30 hops max, 60 byte packets
1 137.112.146.1 (137.112.146.1) 3.968 ms // Skinner switch
2 137.112.9.35 (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-internet
4 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 ms
6 ae-2-2.ebr2.Miami1.Level3.net (4.69.140.141) 31.373 ms
7 ae-1-100.ebr1.Miami1.Level3.net (4.69.151.253) 30.734 ms
The
8 ae-3-5.bar1.Tampa1.Level3.net (4.69.148.214) 36.790 ms
internet
9 ae-5-5.car1.Tampa1.Level3.net (4.69.133.13) 36.164 ms
10 ae-13-13.car3.Tampa1.Level3.net (4.69.133.18) 36.536 ms
11 level3.co1.as30217.net (4.71.0.14) 36.482 ms
12 te3-4.co2.as30217.net (84.40.24.50) 40.225 ms //Wikipedia-internet
13 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
Date: Nov 22 2003
Asia Pacific - Red
Unknown - White
North America - Blue
RFC1918 IP Addresses - Cyan
Latin American and Caribbean - Yellow
Europe/Middle East/Central Asia/Africa - Green
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 view
192.168.1.100 - - [01/Jan/2012:18:51:47 -0500] "GET / HTTP/1.0" 200 44
127.0.0.1 - - [01/Jan/2012:19:04:40 -0500] "GET / HTTP/1.0" 200 44
127.0.0.1 - - [01/Jan/2012:19:05:37 -0500] "GET / HTTP/1.0" 200 44
192.168.1.100 - - [01/Jan/2012:19:06:24 -0500] "GET / HTTP/1.0" 200 44
192.168.1.100 - - [01/Jan/2012:19:08:54 -0500] "GET /.htaccess HTTP/1.0" 403 211
192.168.1.100 - - [01/Jan/2012:19:09:13 -0500] "GET /hmm HTTP/1.0" 404 201
192.168.1.100 - - [01/Jan/2012:19:10:15 -0500] "GET / HTTP/1.0" 200 52
137.112.120.201 - - [02/Jan/2012:22:20:11 -0500] "GET / HTTP/1.1" 200 52
137.112.120.201 - - [02/Jan/2012:22:20:11 -0500] "GET /favicon.ico HTTP/1.1" 404 209
137.112.146.135 - - [02/Jan/2012:23:07:30 -0500] "GET / HTTP/1.1" 200 52
137.112.146.135 - - [02/Jan/2012:23:07:30 -0500] "GET /favicon.ico HTTP/1.1" 404 209
114.205.1.94 - - [02/Jan/2012:23:22:59 -0500] "GET /vhosts/ehcp/?op=applyfordomainaccount HTTP/1.1" 404 210
114.205.1.94 - - [02/Jan/2012:23:23:00 -0500] "GET /ehcp/?op=applyfordomainaccount HTTP/1.1" 404 203
137.112.146.135 - - [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" 403 202
137.112.146.135 - - [03/Jan/2012:01:53:19 -0500] "GET /favicon.ico HTTP/1.1" 403 213
137.112.146.135 - - [03/Jan/2012:01:53:20 -0500] "GET / HTTP/1.1" 403 202
137.112.146.135 - - [03/Jan/2012:01:53:20 -0500] "GET /favicon.ico HTTP/1.1" 403 213
208.25.216.194 - - [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:
Informational
Uncommon.
2x codes:
Success
200: OK
3xx codes:
Redirect
301: permanent
304: not modified
4xx
Client error
403: forbidden
404: not found
5xx:
Server error
500: server broken
501: not implemented
503: server down
Credits
• Map of IPv4 address space:
http://xkcd.com/195/
• Level3 network:
http://www.hcwt.com/level3.php?search_wh
at=level3
• Internet map http://opte.org/maps/