CSCI 5273 Computer Networks Stevens, Chapter 6

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CSCI 5273Computer NetworksStevens, Chapter 6
7Using PING and TRACEROUTE

• Dirk GrunwaldAssoc. ProfessorDept. of Computer
  ScienceUniversity of Colorado, Boulder

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Overview

• Ping sends a ICMP message to a remote host and
  lets you determine if that host is responding
• Traceroute uses TTL fields to query all hosts
  enroute to a specific destination. You can use
  traceroute to map a network.

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PING

• Named after sonar
• Server normally implemented in kernel
• Uses ICMP echo and echo reply messages
• On UNIX, the identifier field is set to Unix PID
  of sending process
• Sequence number starts _at_ 0, incremented every
  time a new echo message is sent

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Sample PING output

• foobar-32 ping gatekeeper.dec.com
• PING gatekeeper.dec.com (204.123.2.2) 56 data
  bytes
• 64 bytes from 204.123.2.2 icmp_seq0 ttl240
  time37 ms
• 64 bytes from 204.123.2.2 icmp_seq1 ttl240
  time35 ms
• 64 bytes from 204.123.2.2 icmp_seq2 ttl240
  time32 ms
• 64 bytes from 204.123.2.2 icmp_seq4 ttl240
  time35 ms
• 64 bytes from 204.123.2.2 icmp_seq6 ttl240
  time37 ms
• 64 bytes from 204.123.2.2 icmp_seq7 ttl240
  time33 ms
• 64 bytes from 204.123.2.2 icmp_seq8 ttl240
  time37 ms
• 64 bytes from 204.123.2.2 icmp_seq9 ttl240
  time54 ms
• 64 bytes from 204.123.2.2 icmp_seq10 ttl240
  time63 ms
• 64 bytes from 204.123.2.2 icmp_seq11 ttl240
  time34 ms
• 64 bytes from 204.123.2.2 icmp_seq12 ttl240
  time36 ms
• ----gatekeeper.dec.com PING Statistics----
• 13 packets transmitted, 11 packets received, 15
  packet loss
• round-trip (ms) min/avg/max 32/40/63 ms

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Details on Output

• Sequence number is shown for each message
• In our example, messages returned in order but
  we lost some packets
• TTL field of return messages displayed
• RTT calculated at the host based on the sequence
  number

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PING to a PPP Connection

• foobar-36 ping dialup-85-30
• PING dialup-85-30.colorado.edu (128.138.85.30)
  56 data bytes
• 64 bytes from 128.138.85.30 icmp_seq0 ttl26
  time441 ms
• 64 bytes from 128.138.85.30 icmp_seq1 ttl26
  time176 ms
• 64 bytes from 128.138.85.30 icmp_seq2 ttl26
  time182 ms
• 64 bytes from 128.138.85.30 icmp_seq3 ttl26
  time188 ms
• ----dialup-85-30.colorado.edu PING Statistics----
• 5 packets transmitted, 4 packets received, 20
  packet loss
• round-trip (ms) min/avg/max 176/247/441 ms
• foobar-37

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Estimating Bandwidth via Ping

• Ping packet is
• 20 byte IP header
• 8 byte ICMP header
• 56-byte message (user settable)
• Total datagram size is 84 bytes
• PPP will add 8 bytes, for total size of 92 bytes
• This connection looks like (92/.180) / 2
  1069 bytes/second
• Or, 8558 bits/s (w/o modem overhead)
• Cheap modem.

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Using PING for sleuthing

• foobar-28 ping www.hotbot.com
• PING www.hotbot.com (216.32.228.18) 56 data
  bytes
• ----www.hotbot.com PING Statistics----
• 2 packets transmitted, 0 packets received, 100
  packet loss
• foobar-29 ping www.hotbot.com
• PING www.hotbot.com (209.185.151.128) 56 data
  bytes
• ----www.hotbot.com PING Statistics----
• 2 packets transmitted, 0 packets received, 100
  packet loss
• foobar-30 ping www.hotbot.com
• PING www.hotbot.com (216.32.228.18) 56 data
  bytes
• ----www.hotbot.com PING Statistics----
• 2 packets transmitted, 0 packets received, 100
  packet loss

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Record Route Option

• Most PING implementations provide record route
• -R option on linux
• -r ltcountgt option on Windows
• Each router stores its address in the IP options
  field
• Only 9 addresses possible
• Thus, round-trip record only possible for 4
  routing hops

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Using the Route Record Option

• why-21 ping -R foobar
• PING foobar.cs.colorado.edu (128.138.241.78) 56
  data bytes
• 64 bytes from 128.138.241.78 icmp_seq0 ttl63
  time4.4 ms
• RR why.cs.colorado.edu (128.138.202.208)
• cs-gw-dmz.cs.colorado.edu
  (128.138.243.193)
• cs-gw3-esl.cs.colorado.edu
  (128.138.241.65)
• foobar.cs.colorado.edu (128.138.241.78)
• cs-gw3-dmz.cs.colorado.edu
  (128.138.243.194)
• cs-gw-hpsc.cs.colorado.edu
  (128.138.202.1)
• why.cs.colorado.edu (128.138.202.208)
• 64 bytes from 128.138.241.78 icmp_seq1 ttl63
  time4.9 ms (same route)
• 64 bytes from 128.138.241.78 icmp_seq2 ttl63
  time4.2 ms (same route)
• 64 bytes from 128.138.241.78 icmp_seq3 ttl63
  time4.1 ms (same route)
• --- foobar.cs.colorado.edu ping statistics ---
• 4 packets transmitted, 4 packets received, 0
  packet loss
• round-trip min/avg/max 4.1/4.4/4.9 ms

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Limitations to PING

• Commonly blocked
• Ping of death

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Traceroute

• Traceroute uses a sequence of ICMP messages to
  determine the current route to a particular
  destination
• The TTL specifies the number of hops a message
  can travel
• traceroute send UDP datagrams while varying the
  TTL
• The router that drops the UDP packet replies with
  a time exceeded ICMP message

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Finding the end

• The end-point wont reply with that ICMP message
• So, traceroute sends to an unlikely UDP port
• Eventually get a no such port ICMP message
• Knows that its reached the end
• Usually...

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Route to Gatekeeper

• foobar-45 traceroute gatekeeper.dec.com
• traceroute to gatekeeper.dec.com (204.123.2.2),
  30 hops max, 40 byte packets
• 1 cs-gw3-esl (128.138.241.65) 1 ms 0 ms 0 ms
• 2 cs-gw-dmz (128.138.243.193) 3 ms 1 ms 2 ms
• 3 engr-cs.Colorado.EDU (128.138.80.141) 2 ms
  2 ms 2 ms
• 4 hut-engr.Colorado.EDU (128.138.80.201) 2 ms
  2 ms 2 ms
• 5 cuatm-gw.Colorado.EDU (128.138.80.2) 2 ms 2
  ms 2 ms
• 6 den-edge-11.inet.qwest.net (205.169.250.49)
  2 ms 5 ms 3 ms
• 7 den-edge-04.inet.qwest.net (205.171.16.169)
  4 ms 2 ms 5 ms
• 8 den-core-01.inet.qwest.net (205.171.16.65) 5
  ms 6 ms 8 ms
• 9 sfo-core-03.inet.qwest.net (205.171.5.35)
  28 ms 27 ms
• 10 sfo-core-02.inet.qwest.net (205.171.18.9) 28
  ms 26 ms 27 ms
• 11 sjo-core-01.inet.qwest.net (205.171.5.121)
  27 ms 27 ms 30 ms
• 12 sjo-edge-05.inet.qwest.net (205.171.22.46)
  31 ms 31 ms 30 ms
• 13 maw-brdr-02.inet.qwest.net (205.171.4.122)
  30 ms 33 ms
• 14 a11-0-0-4.sanjose1-br1.bbnplanet.net
  (4.24.145.1) 35 ms 30 ms 35 ms
• 15 p2-0.sanjose1-nbr1.bbnplanet.net (4.0.3.193)
  33 ms 32 ms 37 ms
• 16 p4-0.paloalto-nbr2.bbnplanet.net (4.0.1.1)
  34 ms 34 ms 40 ms
• 17 p1-0.paloalto-nbr1.bbnplanet.net (4.0.5.65)
  34 ms 35 ms

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Route to Gatekeeper 1

• foobar-45 traceroute gatekeeper.dec.com
• traceroute to gatekeeper.dec.com (204.123.2.2),
  30 hops max, 40 byte packets
• 1 cs-gw3-esl (128.138.241.65) 1 ms 0 ms 0 ms
• 2 cs-gw-dmz (128.138.243.193) 3 ms 1 ms 2 ms
• 3 engr-cs.Colorado.EDU (128.138.80.141) 2 ms
  2 ms 2 ms
• 4 hut-engr.Colorado.EDU (128.138.80.201) 2 ms
  2 ms 2 ms
• 5 cuatm-gw.Colorado.EDU (128.138.80.2) 2 ms 2
  ms 2 ms
• 6 den-edge-11.inet.qwest.net (205.169.250.49)
  2 ms 5 ms 3 ms
• 7 den-edge-04.inet.qwest.net (205.171.16.169)
  4 ms 2 ms 5 ms
• 8 den-core-01.inet.qwest.net (205.171.16.65) 5
  ms 6 ms 8 ms
• 9 sfo-core-03.inet.qwest.net (205.171.5.35)
  28 ms 27 ms

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Route to Gatekeeper 2

• 10 sfo-core-02.inet.qwest.net (205.171.18.9) 28
  ms 26 ms 27 ms
• 11 sjo-core-01.inet.qwest.net (205.171.5.121)
  27 ms 27 ms 30 ms
• 12 sjo-edge-05.inet.qwest.net (205.171.22.46)
  31 ms 31 ms 30 ms
• 13 maw-brdr-02.inet.qwest.net (205.171.4.122)
  30 ms 33 ms
• 14 a11-0-0-4.sanjose1-br1.bbnplanet.net
  (4.24.145.1) 35 ms 30 ms 35 ms
• 15 p2-0.sanjose1-nbr1.bbnplanet.net (4.0.3.193)
  33 ms 32 ms 37 ms
• 16 p4-0.paloalto-nbr2.bbnplanet.net (4.0.1.1)
  34 ms 34 ms 40 ms
• 17 p1-0.paloalto-nbr1.bbnplanet.net (4.0.5.65)
  34 ms 35 ms
• 18 p4-0-0.paix.bbnplanet.net (4.0.6.45) 36 ms
  37 ms 40 ms
• 19 digital-gw1.pa-x.dec.com (4.0.2.114) 40 ms
  34 ms 42 ms
• 20 core-gw1.pa-x.dec.com (204.123.1.1) 38
  ms6 41 ms
• 21 gatekeeper.dec.com (204.123.2.2) 39 ms 35
  ms

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Special features of some traceroutes

• Specify loose source routing
• Specify TOS (type of service) on UDP packet

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Finding routes in our local network

• 128.138.x.y
• 65546 possible IP addresses, not all valid!

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NS lookup
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