ICMP : Internet Control Message Protocol

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ICMP Internet Control Message Protocol

• Computer Network System
• Sirak Kaewjamnong

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Basic Ideas

• ICMP is provided within IP which generates error
  messages to help IP layers(best effort delivery)
• Function of ICMP
• a node recognizing a transmission problem (TTL
  exceed, destination unreachable, etc.) generates
  ICMP messages
• ICMP provides some useful diagnostics about
  network operation (ping, traceroute)

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Basic Ideas

• ICMP error messages never generates due to
• ICMP error message selves
• Broadcast, multicast
• Others fragments, except first fragment
• This to prevent broadcast storm
• What are broadcast storm
• a large number of broadcast datalink frames
  transmitted nearly simultaneous from several
  hosts
• LAN may have been brought to standstill

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ICMP Encapsulation
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ICMP Header

• Type relevant ICMP message
• Code more details information
• Checksum covers ICMP header/data (not IP
  header)

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ICMP Types

• Type Code Meaning
• 0 0 echo reply
• 3 0 network unreachable
• 3 1 host is unreachable
• 3 3 port is unreachable
• 4 0 source quench
• 5 0 redirect
• 8 0 echo request
• 9/10 0 router discovery/advertisement
• 11 0 time exceed
• 12 0 parameter problem
• 13/14 0 time stamp request
• 17/18 0 network request/reply

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ICMP type 0/8 echo request/reply

• PING sends icmp type 8 echo request to a node and
  expects an icmp type 0 echo reply
• identifier and sequence number are used to
  identify datagrams

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ICMP type 3 Destination Unreachable

• Router is unable to deliver datagram, it can
  return the ICMP type 3 with failure code
• Internet header plus 64 bits of original datagram
  are used to identify the datagram caused the
  problem

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ICMP type 4 Source Quench

• Router detected hosts were overload would send
  this message to hosts that were the major cause
• the host would then reduce the rate at which
  subsequence message are sent
• RFC recommends that router must not generate
  source quench, host must still accept the message
  but need take no action

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ICMP type 5 Route Change Request

• Used only by router to suggest a more suitable
  route to the originator (also called ICMP
  redirect)

Type 5
code
checksum
IP address of a more suitable router
IP header 64 bits of original data
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PING ICMP Echo Request/Reply

• PING sends and ICMP echo request to a remote
  host, which then return an ICMP echo reply to the
  sender
• All TCP/IP node is supposed to implement ICMP and
  respond to ICMP echo

PING
Reply
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PING Command

• Send a single echo request message and wait for a
  reply
• Another request is sent if the reply is not
  received within one second
• Continue until at least one reply is received or
  stop after time out
• gt ping maliwan
• maliwan.psu.ac.th is alive
• If maliwan down
• gtping maliwan
• no answer from maliwan.psu.ac.th

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PING Command

• Send an echo request message every seconds and
  records the time it takes for each reply
• every echo request contains a unique sequence
  number to match reply and request
• also record round-trip timing
• also do packet lost statistics

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PING Example

• C\gtping maliwan.psu.ac.th
• Pinging maliwan.psu.ac.th 192.168.100.4 with 32
  bytes of data
• Reply from 192.168.100.4 bytes32 time3ms
  TTL32
• Reply from 192.168.100.4 bytes32 time3ms
  TTL32
• Reply from 192.168.100.4 bytes32 time3ms
  TTL32
• Reply from 192.168.100.4 bytes32 time4ms
  TTL32
• Ping statistics for 192.168.100.4
• Packets Sent 4, Received 4, Lost 0 (0
  loss),
• Approximate round trip times in milli-seconds
• Minimum 3ms, Maximum 4ms, Average 3ms
• C\gt_

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What we get from PING?

• Timing information
• Connection reliability
• Destination Unreachable (routable)

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PING Results

• no respond
• no end node, no connection
• lost packet (significant when gt 2-3 )
• transmission error on LAN/WAN, overloading
  bridge or router
• time acknowledge vary
• host/network overloading gt 100 ms make telnet
  less acceptable
• no lost and echo time is reasonably constant

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Traceroute Command

• Command to determine the active route to a
  destination address
• How?
• Send a UDP message to an unused port on the
  target host with ttl 1
• router decrease ttl to 0, it has to return an
  ICMP time exceed massage
• traceroute set ttl 2 and retransmits, this time
  go one more hop
• ttl until UDP reach the destination
• the target returns an ICMP service unreachable
  because there is no UDP port service

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Traceroute Example

• C\gttracert www.psu.ac.th
• Tracing route to s1.psu.ac.th 192.168.100.61
• over a maximum of 30 hops
• 1 1 ms 1 ms 1 ms
  cs-gw.cs.psu.ac.th 172.28.80.1
• 2 2 ms 2 ms 1 ms esw-cc.psu.ac.th
  192.168.99.39
• 3 2 ms 3 ms 5 ms cc-atm.psu.ac.th
  192.168.0.249
• 4 4 ms 2 ms 3 ms tooky.psu.ac.th
  192.168.98.11
• 5 3 ms 3 ms 3 ms s1.psu.ac.th
  192.168.100.61
• Trace complete.
• C\gt
• usually probes each hop 3 times
• a lost message or a router that doesnt respond
  with denote with an