Skip to main content

4. ICMPv6 Informational Messages

4.1. Echo Request Message​

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Identifier          |        Sequence Number        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Data ...
   +-+-+-+-+-

IPv6 Fields:

Destination Address: Any legal IPv6 address.

ICMPv6 Fields:

Type: 128

Code: 0

Identifier: An identifier to aid in matching Echo Replies to this Echo Request. May be zero.

Sequence Number: A sequence number to aid in matching Echo Replies to this Echo Request. May be zero.

Data: Zero or more octets of arbitrary data.

Description

Every node MUST implement an ICMPv6 Echo responder function that receives Echo Requests and originates corresponding Echo Replies. A node SHOULD also implement an application-layer interface for originating Echo Requests and receiving Echo Replies, for diagnostic purposes.

Upper Layer Notification

Echo Request messages MAY be passed to processes receiving ICMP messages.

4.2. Echo Reply Message​

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Identifier          |        Sequence Number        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Data ...
   +-+-+-+-+-

IPv6 Fields:

Destination Address: Copied from the Source Address field of the invoking Echo Request packet.

ICMPv6 Fields:

Type: 129

Code: 0

Identifier: The identifier from the invoking Echo Request message.

Sequence Number: The sequence number from the invoking Echo Request message.

Data: The data from the invoking Echo Request message.

Description

Every node MUST implement an ICMPv6 Echo responder function that receives Echo Requests and originates corresponding Echo Replies. A node SHOULD also implement an application-layer interface for originating Echo Requests and receiving Echo Replies, for diagnostic purposes.

The source address of an Echo Reply sent in response to a unicast Echo Request message MUST be the same as the destination address of that Echo Request message.

An Echo Reply SHOULD be sent in response to an Echo Request message sent to an IPv6 multicast or anycast address. In this case, the source address of the reply MUST be a unicast address belonging to the interface on which the Echo Request message was received.

The data received in the ICMPv6 Echo Request message MUST be returned entirely and unmodified in the ICMPv6 Echo Reply message.

Upper Layer Notification

Echo Reply messages MUST be passed to the process that originated an Echo Request message. An Echo Reply message MAY be passed to processes that did not originate the Echo Request message.

Note that there is no limitation on the amount of data that can be put in Echo Request and Echo Reply Messages.

Last updated on