CS459 Internet Measurements

Transcription

1 CS459 Internet Measurements Introduction to Traceroute and iplane Spring 2015

2 Traceroute Tool used to trace the path from source to destination host. TCP/IP not designed for traceroute, so it is sometimes unpredictable. traceroute from a host in Los Angeles to the BBC website in London. 1

3 Traceroute Displays the entire path followed by the outgoing packets to reach the destination host. Names and identity of routers and devices in the path. Measures the transit delay for reaching each node along the path to the destination. Windows use an ICMP-based traceroute utility - tracert. Sends ICMP echo request (ICMP Type 8 ) packets to the destination (ping). Unix, Linux and BSD systems use a UDP-based traceroute. Sends UDP packets to the destination, with destination port ranging from to

4 Traceroute Operation Packet sent from source to destination contain a TTL value (number of permitted hops). Each router that handles a packet subtracts one from the packet s TTL and forwards it to the next router in the path. If the TTL reaches zero, the packet is considered as expired and thus, it is discarded (not forwarded to the next router). At this point, most routers send an ICMP Time Exceeded message back to the sender. This message contains the IP address of the specific device. Traceroute uses these messages to identify the route 3

5 TTL = 1 Traceroute Operation 4

6 TTL = 1 Traceroute Operation TTL = 0 4

7 TTL = 1 Traceroute Operation TTL = 0 ICMP Time Exceeded (ICMP Type 11) 4

8 TTL = 2 Traceroute Operation TTL = 1 4

9 TTL = 2 Traceroute Operation TTL = 1 TTL = 0 4

10 TTL = 2 Traceroute Operation TTL = 1 TTL = 0 ICMP Time Exceeded 4

11 TTL = 3 Traceroute Operation TTL = 2 TTL = 1 TTL = 0 ICMP Time Exceeded 4

12 TTL = 4 Traceroute Operation TTL = 3 TTL = 2 TTL = 1 ICMP Reply (Type 0 ) 4

13 Traceroute Operation The sender sends 3 packets per hop (default) The sender keeps the time each message is sent, and compares it with the time every ICMP time exceeded packet is received Thus, it estimates the delay of each hop in the path. IP address and hostname of each device in the path becomes known (if router settings/firewalls does not prevent it). 5

14 Linux Traceroute Try it now Open a terminal: -> traceroute mailhost.csd.uoc.gr -> traceroute -> traceroute Check out the Traceroute Man Page: - I [use ICMP ECHO for probes] - T [use TCP SYN for probes] - m [max ttl] - N [number of simultaneous probes] 6

15 Traceroute Example 1 Hop 1: Home LAN router, Hops 5-6: Level 3 backbone Hops 2-4: My ISP s backbone Hops 7-10: Facebook s Network Results for 8 & 9 indicate that the router security settings keep them from revealing their identity (most probable), or that the router/connection is slow. 7

16 Traceroute Example 2 8

17 Building the Atlas of the Internet Traceroute shows the route a packet follows, from a single source to a single destination source. However, we miss other paths (e.g. the route followed by the response packets). We miss existing links/connections. What if we combine different paths? Can we build the atlas of the Internet? 9

18 iplane A topology collection research project run by the University of Washington on PlanetLab. o PlanetLab is a global network of academic research servers. Performs traceroutes to a random sample of BGP prefixes, daily, since iplane constructs an annotated map of the topology of the Internet, focusing on core Internet backbones that contain most of the used paths. 10

19 iplane Data Daily traceroute files from all the PlanetLab nodes, since For the purposes of the 1 st assignment we will need the traces that describe the first Monday of the first month of each season from 2007 to (first Monday of March, June, Sept and December). The datasets required for the assignment have been downloaded in the spare partition of fistiki.csd.uoc.gr (/spare/hy459/iplane.cs.ucr.edu/iplane_logs/..). 11

20 iplane Data Tracefiles for Sep Tracefiles for Dec Follow the original hierarchy of iplane, <year>/<month>/<day>/ From 2010/12 iplane stores tracefiles in in pl_traces directory 12

21 Archive of a specific day Three kind of files index.out.<vantage_point> count.out.<vantage_point> trace.out.<vantage_point> You will only use trace.out files for the assignment. 13

22 iplane Data Follow the original hierarchy of iplane, <year>/<month>/<day>/ for Dec. 01,

23 iplane Data Format Use readoutfile tool to read out each trace.out.* file already compiled in /spare/hy459/readoutfile 15

24 Reading a tracefile Traceroute from: planetlab1.cs.columbia.edu to:

25 Parse the tracefiles Use whichever programming language you like - You can even modify the readoutfile tool according to your needs But, we highly recommend to use a scripting language (e.g. shell scripting, awk, sed etc) - Very flexible - Speed of development - Good opportunity to get familiar with 17

26 Example 1 Find the hops contained in all traceroutes initiated by planetlab2.cs.uoi.gr in 2014 (Mar, Jun, Sep, Dec). Find all the destination hosts, for all the traceroutes performed in the first Monday of March

27 Example 2 Print the path from planetlab2.cs.uoi.gr to each destination point, in a single line each 19

28 Example 3 Print the latency between planetlab2.cs.uoi.gr and for the first day of each season in Use awk to select specific columns 20

29 Example 3 Print the latency between planetlab2.cs.uoi.gr and for the first day of each season in Use awk to select specific columns - Assign the result of a specific command to a variable - Print formatted output 21