Selecting best Redhat Mirror Sites for parallel download Jing Yang and Zhong Li CS522 Semester Proje

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Selecting best Redhat Mirror Sites for parallel
downloadJing Yang and Zhong LiCS522 Semester
Project
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Selecting the best mirror sites for parallel
download

• Investigate traceroute and pathchar to
  characterize the top Redhat mirror sites of
  interest to UCCS(wait.uccs.edu)
• Apply traceroute to get shortest round trip time
  (rrt) values and netowrk topology.
• Apply pathchar to estimate the bandwidth of the
  links along which the packet flow.

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• Traceroute and Pathchar Programs
• Traceroute utilizes IP protocol time to live
  field and attempts to elicit an ICMP
  TIME_EXCEEDED responses from each gateway along
  the path to some host and therefore obtain the
  round trip time(rtt). (designed by Jacobson)
• Pathchar correlates rtt with packet length to
  estimate the bandwidth. Pathchar provides more
  detailed and precise information by sending many
  differenet probe packets to each link. (designed
  by Van Jacobson)

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Apply Traceroute for Topology

• -70 Redhat mirror websites from north America
  were chosen for running traceroute
• ttl is originally set to1 and increased by one
  each time the packet is sent to further host.
• ttl is decreased by each gateway and when ttl
  becomes zero, the gateways ends back a ICMP time
  exceeded message.

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Traceroute Execution Result

• When we get an ICMP port unreachable, does it
  mean we have reached the destination?
• zli_at_wait trace traceroute limestone.uoregon.edu
  
• traceroute to limestone.uoregon.edu
  (128.223.162.20), 30 hops max, 38 byte packets
• 1 cs-content-switch1-router (128.198.60.1)
  0.403 ms 1.000 ms 0.833 ms
• 2 uccsedge (128.198.254.9) 3.153 ms 3.828 ms
  2.830 ms
• 3 uccs-link-at-frgp (128.198.254.2) 3.230 ms
  3.361 ms 3.196 ms
• 4 ucar.edu.ip.att.net (12.124.158.13) 3.752 ms
  3.754 ms 3.970 ms
• 17 p10-0-0.mit2.bbnplanet.net (4.1.80.10)
  83.610 ms 146.916 ms 83.738 ms
• 18 b24-rtr-1-backbone.mit.edu (18.168.0.14)
  88.859 ms 88.080 ms 88.964 ms
• radole.lcs.mit.edu (18.201.1.3) 88.724 ms
  88.153 ms 91.810 ms 
• 21 rufus.w3.org (18.29.1.67) 268.701 ms
  223.507 ms 241.069 ms
•  
•  

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How Pathchar Works

• - local host sends 32 probe packets (by
  default) for each different size ranging from 64
  bytes to 1500 bytes (45 times)
• Some parameters can be passed in the command
  line
• -f initial hop , -l max ttl, -q
  queries for more info checkhttp//www.cai.org/t
  ools/utilities/others/pathchar/pathcharnotes.html
• - It correlates rrt with packet length to
  estimate bandwidth

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Pathchar Execution Example

• pathchar to trillian.cc.gatech.edu
  (130.207.108.135)
• can't find path mtu - using 1500 bytes.
• doing 32 probes at each of 45 sizes (64 to 1500
  by 32)
• 0 localhost
• 27 Mb/s, 155 us (758 us)
• 1 cs-content-switch1-router (128.198.60.1)
• 97 Mb/s, 179 us (1.24 ms)
• 2 uccsedge (128.198.254.9).
• .
• 14 130.207.251.2 (130.207.251.2)
• ?? b/s, 356 us (94.8 ms)
• 15 cc-rstone-sys3-156.cc.gatech.edu
  (130.207.108.158)
• 54 Mb/s, 154 us (95.3 ms), 33 dropped
• 16 trillian.cc.gatech.edu (130.207.108.135)
• 16 hops, rtt 93.5 ms (95.3 ms), bottleneck 27
  Mb/s, pipe 319241 bytes
• 
  

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Interpretation of Pathchar Output

• the last line shows the output of this pathchar
  run there are totally 15 gateways involved(16 is
  the destination) bottleneck is 27 Mb/s which
  occurs between the local host and
  cs-content-switch1-router (128.198.60.1)
• Tree diagram shows the result of running pathchar
  on all websites(each run takes 4-5 hours)

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Wait to Redhat Mirror Sites Tree
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Algorithm for Selecting Top Mirror Sites (Steps
1-3)

• 1. Sort the all the bottleneck values in
  decreasing order and put in array Atotal number
  of websites
• 2. choose the domain name with bottleneck A0 as
  the first website and put in the final result
  array Snumber of domain names sorted
• 3. Find all the nodes where the host with next
  bottleneck can merge with other nodes (if has
  some). If not put domain name with the bottleneck
  in A, choose next value in A and go back to 3.

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Algorithm for Selecting Top Mirror Sites (Steps
4-6)

• 4. Find all the bandwidths between the merged
  nodes and their previous nodes.
• 5. Compare each bandwidth with the sum of
  bottlenecks of hosts that merge, if the sum does
  not exceed the bandwidth, put the domain name
  with the next bottleneck in array, choose the
  next value in array A and go back to 3.
• 6. If the sum is larger than bandwidth, choose
  the next value in array A and go back to 3.

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Algorithm for Selecting Top Mirror Sites (Step 7)

• 7. Keep doing this until all hosts in array A are
  put in array S.
• list of top five websites selected for UCCS
  (wait.uccs.edu)
• 1. true-love.rutgers.edu
• 2. ubu.nws.orst.edu
• 3. atlas.services.ou.edu
• 4. www.cio.ohio-state.edu
• 5. Fillmore.ind.net

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Reference

• http//redhat.com.download/mirror.html
• http//www.cai.org/tools/utilities/others/pathchar
  /pathcharnotes.html
• http//www-iepm.slac.stanford.edu/monitoring/load/
  pathchar.html
• http//sitka.triumf.ca/net/pathchar.html
• http//www.fips.de/Computer/man/pathchar.html