icmp v4 and icmp v6

ICMP v4 and ICMP v6

ICMP overview

• Delivery method of IP is– connectionless, unreliable and unacknowledged.

• In TCP/IP, diagnostic, test and error-reporting functions at the internet/network layer are performed by the Internet Control Message Protocol (ICMP)

• ICMP is the Internet Protocol’s “administrative assistant”.

• The original version, now called ICMPv4, is used with IPv4, and the newer ICMPv6 with IPv6.

ICMP General operation

Limitations

• ICMP error-reporting messages can only be sent back to the originating device.– Intermediate devices cannot be the recipient

of an ICMP message – Because their addresses are normally not

carried in the IP datagram’s header.

ICMP messages• ICMP messages are divided into two general

categories: – error messages that are used to report problem

conditions– informational messages that are used for diagnostics,

testing and other purposes.

• Total 256 messages each for ICMPv4 & ICMPv6.

• In ICMPv4 there is no relationship between Type value and message type

• In ICMPv6 error messages have a Type value of 0 to 127, informational messages 128 to 255.

ICMPv4 Error messages

• Type Value: 3• Message Name : Destination Unreachable

• Summary of Message Type: – Indicates that a datagram could not be delivered

to its destination. The Code value provides more information on the nature of the error.


• Type Value: 4

• Message Name : Source Quench

• Summary of Message Type: – Lets a congested IP device tell a device

that is sending it datagrams to slow down the rate at which it is sending them.


• Type Value: 5

• Message Name : Redirect

• Summary of Message Type: – Allows a router to inform a host of a better

route to use for sending datagrams.


• Type Value: 11

• Message Name : Time Exceeded

• Summary of Message Type: – Sent when a datagram has been discarded

prior to delivery due to expiration of its Time To Live field.


• Type Value: 12

• Message Name : Parameter Problem

• Summary of Message Type: – Indicates a miscellaneous problem

(specified by the Code value) in delivering a datagram.

ICMPv4 Informational messages

• Type Value: 0

• Message Name : Echo Reply

• Summary of Message Type: – Sent in reply to an Echo (Request)

message; used for testing connectivity.


• Type Value: 8

• Message Name : Echo (Request)

• Summary of Message Type: – Sent by a device to test connectivity to

another device on the internetwork. The word “Request” sometimes appears in the message name.


• Type Value: 9

• Message Name : Router Advertisement

• Summary of Message Type: – Used by routers to tell hosts of their

existence and capabilities.


• Type Value: 10

• Message Name : Timestamp (Request)

• Summary of Message Type: – Sent by a device to request that another

send it a timestamp value for propagation time calculation and clock synchronization. The word “Request” sometimes appear in the message name.


• Type Value: 8

• Message Name : Echo (Request)

• Summary of Message Type: – Sent by a device to test connectivity to

another device on the internetwork. The word “Request” sometimes appears in the message name.


• 14 Timestamp Reply

• 17 Address Mask Request

• 18 Address Mask Reply

• 30 Traceroute


• Type Value: 1

• Message Name : Destination Unreachable

• Summary of Message Type: – Indicates that a datagram could not be

delivered to its destination. Code value provides more information on the nature of the error.


• Type Value: 2• Message Name : Packet Too Big• Summary of Message Type:

– Sent when a datagram cannot be forwarded because it is too big for the maximum transmission unit (MTU) of the next hop in the route. This message is needed in IPv6 and not IPv4 because in IPv4, routers can fragment oversized messages, while in IPv6 they cannot.


• Type Value: 3

• Message Name : Time Exceeded

• Summary of Message Type: – Sent when a datagram has been discarded

prior to delivery due to the Hop Limit field being reduced to zero.


• Type Value: 4

• Message Name : Parameter Problem

• Summary of Message Type: – Indicates a miscellaneous problem

(specified by the Code value) in delivering a datagram


• 128 Echo Request• 129 Echo Reply• 133 Router Solicitation• 134 Router Advertisement• 135 Neighbor Solicitation• 136 Neighbor Advertisement• 137 Redirect• 138 Router Renumbering

Error message rules

ICMP error message must not be generated in response to any of the following:

• An ICMP Error Message: This prevents loops. Note, however, that an ICMP error message can be generated in response to an ICMP informational message.

• A Broadcast or Multicast Datagram: • IP Datagram Fragments Except The First• Datagrams With Non-Unicast Source

Address:

ICMP common format

icmp v4 and icmp v6

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