1. Byungchul Park (fates@postech.ac.kr)
ICMP & ICMPv6
DPNM Lab.
Byungchul Park

2. Internet Control Message Protocol
ICMP
Internet Control Message Protocol

3. Introduction ICMP is often considered part of the IP layer
ICMP: Internet Control Message Protocol
ICMP is often considered part of the IP layer
Why the ICMP is needed?
Lacks of IP !!!
Unreliable and connectionless datagram delivery
Best-effort delivery service
Lack of error control and lack of assistance mechanisms
No error-reporting and error-correcting mechanisms
Lacks of mechanism for host and management queries
 ICMP has been designed to compensate for the above deficiencies.
Application
Telnet, FTP, , etc
Transport
TCP, UDP
Network
IP, ICMP, IGMP
Link
device driver and interface card

4. Introduction ICMP message are transmitted within IP datagrams
ICMP: Internet Control Message Protocol
ICMP message are transmitted within IP datagrams
Although ICMP is used primarily by IP, it is possible for an application to also access it. (e.g. Traceroute, Ping)

5. ICMP Messages ICMP message are transmitted within IP datagrams
Types of Messages
ICMP message are transmitted within IP datagrams
Error reporting : report problems that a router or host may encounter when it processes an IP packet
Query message : get specific information from router or a host in order to help a host or network management.
ICMP Messages
Error-reporting
Query

6. ICMP Messages (cont.) Category Type Message Error-reporting message 3
Types of Messages
Category
Type
Message
Error-reporting message 3
Destination unreachable 4
Source quench 11
Time exceeded 12
Parameter problem 5
Redirection
Query message
8 or 0
Echo request or reply
13 or 14
Timestamp request and reply
17 or 18
Address mask request and reply
10 or 9
Router solicitation and advertisement

7. Message Format Type : message type(8 bit)
ICMP Message Format
Type : message type(8 bit)
Code : specify the reason for the particular message
Checksum : 16 bit

8. Message Format Address mask reply 18 Address mask request 17
ICMP common field and message Type
Address mask reply 18
Address mask request 17
Timestamp reply 14
Timestamp request 13
Parameter problem
0-1 12
Time exceeded 11
Router solicitation 10
Router advertisement 9
Echo request 8
Redirection
0-3 5
Source quench 4
Destination unreachable
0-15 3
Echo reply
description
code
Type

9. IP, as an unreliable protocol, is not concerned with error checking and error control. ICMP was designed, in part, to compensate for this shortcoming. ICMP does not correct errors, it simply reports them.

10. ICMP always reports error messages to the original source.
Error Reporting
ICMP: Internet Control Message Protocol
Main responsibilities of ICMP
Error messages are always sent to the original source
ICMP always reports error messages to the original source.
Error Reporting
Time
exceeded
Source
quench
Parameter
problems
Redirection
Destination
unreachable

11. Error Reporting
Contents of data field for error messages
When an ICMP error message is sent, the message always contains the IP header and the first 8 bytes of the IP datagram that caused the ICMP error to be generated.

12. Error Reporting
Destination Unreachable
When a router cannot route a datagram or a host cannot deliver a datagram, the datagram is discarded and the router or host send s a destination unreachable message back to the source.
Format
Destination-unreachable messages with codes 2 or 3 can be created only by the destination host. Other destination-unreachable messages can be created only by routers.
A router cannot detect all problems that prevent the delivery of a packet
There is no flow-control mechanism in the IP protocol.

13. Error Reporting Code Field : the reason for discarding the datagram
Destination Unreachable
Code Field : the reason for discarding the datagram
code
Reasons for error
Network unreachable 1
Host unreachable 2
Protocol unreachable 3
Port unreachable 4
Fragmentation needed and DF set 5
Source route failed 6
Destination network unknown 7
Destination host unknown 8
Source host isolated 9
Communication with destination network administratively prohibited 10
Communication with destination host administratively prohibited 11
Network unreachable for type of services 12
Host unreachable for type of services

14. Error Reporting
Time-Exceeded message
Code 0 is used only by routers to show that the value of the time-to-live field is zero.
Code 1 is used only by the destination host to show that not all of the fragments have arrived within a set time.
Whenever a router receives a datagram with a time-to-live value of zero, it discards the datagram and sends a time-exceeded message to the original source.
When the final destination does not receive all of the fragments in a set time, it discards the received fragments and sends a time-exceeded message to the original source.
Format

15. Error Reporting Code 0: Main header problem
Parameter problem
Code 0: Main header problem
Code 1: Problem in the option field
A parameter-problem message can be created by a router or the destination host.
Format

16. Error Reporting
Redirection concept
When a host send a datagram, which is destined for another network, to the wrong router, the router that receives the datagram will forward the datagram to the correct router. However, to update the routing table of host, it send a redirection message to host.
When a new host come up, its routing table has a limited number of entries. It usually knows only a default router, so they can send to wrong router.

17. Error Reporting
Redirection concept
A redirection message is sent from a router to host on the same local network.
Redirection message format
Code 0: Network specific Code 1: Host specific Code 2: Network specific (specified service)
Code 3: Host specific (specified service)
Format

18. ICMP can also diagnose some network problems through the query messages, a group of four different pairs of messages. In this type of ICMP message, a node sends a message that is answered in a specific format by the destination node.

19. Query Diagnose some network problems Query messages Query Timestamp
ICMP: Internet Control Message Protocol
Diagnose some network problems
Query messages
Query
Timestamp
request & reply
Address mask
Request & reply
Router solicitation
& advertisement
Echo

20. Query
Echo Request and Reply
An echo-request message can be sent by a host or router. An echo-reply message is sent by the host or router which receives an echo-request message.
Echo-request and echo-reply messages can be used by network managers to check the operation of the IP protocol
Echo-request and echo-reply messages can test the reachability of a host. this is usually done by invoking the ping command.

21. Query
Timestamp Request and Reply
The timestamp-request and timestamp-reply messages can be used to synchronize two clocks in two machines if the exact one-way time duration is known.
Timestamp-request and timestamp-reply messages can be used to calculate the round-trip time between a source and a destination machine even if their clocks are not synchronized.
Each field is represented by the unit of Miliseconds from midnight in Universal Time
3 timestamp fields(original, receive, transmit) are 32 bit long, (0~4,294,967,295), but a timestamp in this case cannot exceed 86,400,000= 24x60x60x1000.

22. Query Format Steps Sender create a timestamp-request message
Timestamp Request and Reply
Format
Steps
Sender create a timestamp-request message
Insert the sending time to Original timestamp field
Other 2 fields is 0
Receiver create the timestamp-reply message
Copy the value of the original timestamp to same field
Insert the receiving time of the request message to the receive timestamp
Insert the sending time of the reply message to the transmit timestamp.

23. Query
Address-Mask Request and Reply
When a host want to know about a full IP address which part of address defines the network and subnetwork address and which part corresponds to the host identifier.
Masking is needed for diskless station at statr-up time.(BOOTP protocol)
Mask-request and mask-reply message format

24. Query
Router solicitation and Advertisement
A host the want to send data to a host on outside network needs to know the address of routers connected to its own network.
A host can broadcast(or multicast) a router-solicitation message
A router or routers that received the solicitation message broadcast their routing information using the router-advertisement message.
Router-solicitation message format

25. Query Router advertisement message format
Router solicitation and Advertisement
Router advertisement message format
The preference level is used to select a router as the default router.
If the preference level is 0, the router is considered the default router.
If the preference level is , the router should be never selected as the default router.

26. ICMPv6
Internet Control Message Protocol Version 6

27. Comparison of network layers in IPv4 and IPv 6
ICMPv6: Internet Control Message Protocol version 6

28. Message Format General format of ICMPv6 messages
Router solicitation and Advertisement
General format of ICMPv6 messages

29. Error Reporting Error Reporting Time exceeded Packet too big Parameter
Router solicitation and Advertisement
Error Reporting
Time
exceeded
Packet too big
Parameter
problems
Redirection
Destination
unreachable

30. Destination unreachable
Error Reporting
Comparison Error Reporting function between v4 and v6
Type of Message V4 V6
Destination unreachable
Yes
Source quench No
Packet too big
Time exceeded
Parameter problem
Redirection

31. Neighbor solicitation
Query
ICMPv6: Internet Control Message Protocol version 6
Diagnose some network problems
Query messages
Query
Echo
request & reply
Group
membership
Neighbor solicitation
& advertisement
Router solicitation
& advertisement

32. Query Type of Message V4 V6 Echo request and reply Yes
ICMPv6: Internet Control Message Protocol version 6
Type of Message V4 V6
Echo request and reply
Yes
Timestamp request and reply No
Address mask request and reply
Router solicitation
Neighbor solicitation
ARP
Group membership
IGMP

33. ?