1. Reading for next class No new reading, but there will be a quiz Ch 4.1 – 4.23: Internet applications

2. Review: Traceroute 3 probes Local host: Alice Remote host: Jack Probe successive hops to find network path – sends 3 packets that will reach each router on path towards destination – Each router returns packets to sender – sender times interval between transmission and reply.

3. Review: Traceroute Local host: Alice Remote host: Jack Technically, a hop is defined as the action that occurs when a packet “jumps” from one router to the next. 1 hop 2 hop 3 hop N-1 hop N hop

4. Traceroute Example 1 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net (140.222.27.221) 2. 100ms 120ms 140ms New-York2.t3.ans.net (140.223.37.9) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net (40.1.122) 4 339ms 279ms 279ms Allspice.lcs.mit.edu (18.26.0.115) 3 delay measurements

5. Traceroute Question 6 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net (140.222.27.221) 2. 100ms 120ms 140ms New-York2.t3.ans.net (140.223.37.9) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net (40.1.122) 4 339ms 279ms 279ms Allspice.lcs.mit.edu (18.26.0.115) How many computers are there in this route? How many hops?

6. Traceroute Question 7 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net (140.222.27.221) 2. 100ms 120ms 140ms New-York2.t3.ans.net (140.223.37.9) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net (40.1.122) 4 339ms 279ms 279ms Allspice.lcs.mit.edu (18.26.0.115) How many packets are sent by local host? How many packets are forwarded by New York (New- York2.t3.ans.net )?

7. Traceroute Question 8 C:\> tracert allspice.lcs.mit.edu 1 20ms 25ms 15ms philadelphia4.t3.ans.net (140.222.27.221) 2. 100ms 120ms 140ms New-York2.t3.ans.net (140.223.37.9) 3 300ms 280ms 260ms Cambridge1.bbnplanet.net (40.1.122) 4 339ms 279ms 279ms Allspice.lcs.mit.edu (18.26.0.115) What’s the average round trip time form local host to Cambridge1.bbnplanet.net?

8. Traceroute Example 2 C:\> tracert www.oxford.ac.uk 1 85 ms 1 ms 1 ms 192.168.1.1 2 9 ms 11 ms 9 ms c-71-58-208-1.hsd1.pa.comcast.net [71.58.208.1] 3 11 ms 10 ms 10 ms te-0-7-0-6-sur02.statecollege.pa.pitt.comcast.net [162.151.68.245] 4 17 ms 15 ms 15 ms be-3-ar03.lowerpaxton.pa.pitt.comcast.net [69.139.194.81] 5 21 ms 21 ms 27 ms he-0-15-0-0-ar01.pittsburgh.pa.pitt.comcast.net[69.139.168.185] 6 45 ms 31 ms 32 ms be-7016-cr01.newyork.ny.ibone.comcast.net [68.86.91.29] 7 29 ms 28 ms 29 ms ae12.edge1.NewYork2.level3.net [4.68.127.1] 8 145 ms 302 ms 306 ms ae-4-4.car1.Manchesteruk1.Level3.net [4.69.133.101] 9 116 ms 210 ms 207 ms ae-4-4.car1.Manchesteruk1.Level3.net [4.69.133.101] 10 107 ms 103 ms 106 ms 195.50.119.98 11 107 ms 107 ms 107 ms ae29.erdiss-sbr1.ja.net [146.97.33.41] 12 114 ms 106 ms 106 ms ae31.londpg-sbr1.ja.net [146.97.33.21] 13 109 ms 109 ms 109 ms ae21.read-rbr3.ja.net [146.97.37.206] 14 106 ms 117 ms 105 ms ae1.read-rbr2.ja.net [193.63.108.129] 15 108 ms 107 ms 107 ms ae2.oxfo-rbr2.ja.net [193.63.108.134] 16 108 ms 107 ms 107 ms Oxford-University-2.ja.net [193.63.109.114] 17 109 ms 110 ms 108 ms csurb.backbone.ox.ac.uk [192.76.21.21] 18 281 ms 110 ms 110 ms boucs.backbone.ox.ac.uk [192.76.22.200] 19 106 ms 107 ms 107 ms boucs-lompi1.sdc.ox.ac.uk [192.76.32.62] 20 109 ms 109 ms 108 ms aurochs-web-154.nsms.ox.ac.uk [129.67.242.154] Trace complete. Level3: Trans-atlantic link comcast Janet: UK’s research network oxford

9. Traceroute Exercise 1 Step 1: Start  Run  cmd Step 2: Trace route to – Somewhere in the U.S. – Somewhere outside U.S. Discuss the results with classmates next to you – How may hops are there in the path? – What’s the average delay from you computer to the remote host? – How many major networks does the path traverse? What are they? – For destination outside US, from which router do the packets leave US?

10. Traceroute Exercise 2 For this exercise, you need to use the traceroute server at http://www.slac.stanford.edu/cgi-bin/nph- traceroute.pl. When you view this web page, execute a traceroute (trace) to:http://www.slac.stanford.edu/cgi-bin/nph- traceroute.pl 1.your machine 2.Somewhere in US 3.Somewhere outside US

11. Traceroute Exercise 3 At the command prompt, type: – tracert 18.31.0.200 Describe what is strange about the observed output, and why traceroute gives you such an output