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ICMP : Internet Control Message Protocol

ICMP : Internet Control Message Protocol. Computer Network System Sirak Kaewjamnong. Basic Ideas. ICMP is provided within IP which generates error messages to help IP layers(best effort delivery) Function of ICMP

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ICMP : Internet Control Message Protocol

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  1. ICMP : Internet Control Message Protocol Computer Network System Sirak Kaewjamnong

  2. 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)

  3. 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

  4. Indicate error problems Type Code ……. Contain protocol indicate ICMP IP header IP Data Frame header e.g. Ethernet Frame Data ICMP Encapsulation

  5. 0 15 16 31 Type: 8 Code : 8 Checksum : 16 Content specific ICMP Header • Type : relevant ICMP message • Code : more details information • Checksum : covers ICMP header/data (not IP header)

  6. 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

  7. Type = 0 or 8 code checksum identifier Sequence number Optional data 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

  8. Type = 3 code checksum unused IP header + 64 bits of original data 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

  9. Type = 4 code checksum Unused (must be 0) IP header + 64 bits of original data 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

  10. 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

  11. 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

  12. 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 > ping maliwan maliwan.psu.ac.th is alive If maliwan down >ping maliwan no answer from maliwan.psu.ac.th

  13. 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

  14. PING Example C:\>ping maliwan.psu.ac.th Pinging maliwan.psu.ac.th [192.168.100.4] with 32 bytes of data: Reply from 192.168.100.4: bytes=32 time=3ms TTL=32 Reply from 192.168.100.4: bytes=32 time=3ms TTL=32 Reply from 192.168.100.4: bytes=32 time=3ms TTL=32 Reply from 192.168.100.4: bytes=32 time=4ms TTL=32 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:\>_

  15. What we get from PING? • Timing information • Connection reliability • Destination Unreachable (routable)

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

  17. 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

  18. Traceroute Example C:\>tracert 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:\> • usually probes each hop 3 times • a lost message or a router that doesn’t respond with denote with an “ * “

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