ICMP

• Internet Control Message Protocol - L3, primarily used for error-reporting
  • not associated w TCP or UDP - connectionless
  • cannot target a specific port

• ping sends ICMP echo request packets

  • hosts reply w ICMP echo reply packets

• windows ping sends 4 echo requests, while linux ping sends continuously

  • linux (cont) on windows: ping -t 192.168.1.1
  • windows (4) on linux: ping -c 4 192.168.1.1

• kinds of ICMP messages

  • 0 - time exceeded
    • traceroute uses this one to get its data back to sender
  • 3 - destination unreachable
  • 8 - echo request
  • 9 - router advertisement
  • 10 - router solicitation
  • 11 - time exceeded