rfc4443-icmpv6(2006).txt

本备忘录的状态 本文档讲述了一种Internet社区的Internet标准跟踪协议

             from e.3 apply to this case, too).




Conta, et al.               Standards Track                     [Page 6]

RFC 4443                 ICMPv6 (ICMP for IPv6)               March 2006


       (e.5) A packet sent as a link-layer broadcast (the exceptions
             from e.3 apply to this case, too).

       (e.6) A packet whose source address does not uniquely identify a
             single node -- e.g., the IPv6 Unspecified Address, an IPv6
             multicast address, or an address known by the ICMP message
             originator to be an IPv6 anycast address.

   (f) Finally, in order to limit the bandwidth and forwarding costs
       incurred by originating ICMPv6 error messages, an IPv6 node MUST
       limit the rate of ICMPv6 error messages it originates.  This
       situation may occur when a source sending a stream of erroneous
       packets fails to heed the resulting ICMPv6 error messages.

       Rate-limiting of forwarded ICMP messages is out of scope of this
       specification.

       A recommended method for implementing the rate-limiting function
       is a token bucket, limiting the average rate of transmission to
       N, where N can be either packets/second or a fraction of the
       attached link's bandwidth, but allowing up to B error messages to
       be transmitted in a burst, as long as the long-term average is
       not exceeded.

       Rate-limiting mechanisms that cannot cope with bursty traffic
       (e.g., traceroute) are not recommended; for example, a simple
       timer-based implementation, allowing an error message every T
       milliseconds (even with low values for T), is not reasonable.

       The rate-limiting parameters SHOULD be configurable.  In the case
       of a token-bucket implementation, the best defaults depend on
       where the implementation is expected to be deployed (e.g., a
       high-end router vs. an embedded host).  For example, in a
       small/mid-size device, the possible defaults could be B=10,
       N=10/s.

   NOTE: THE RESTRICTIONS UNDER (e) AND (f) ABOVE TAKE PRECEDENCE OVER
   ANY REQUIREMENT ELSEWHERE IN THIS DOCUMENT FOR ORIGINATING ICMP ERROR
   MESSAGES.

   The following sections describe the message formats for the above
   ICMPv6 messages.









Conta, et al.               Standards Track                     [Page 7]

RFC 4443                 ICMPv6 (ICMP for IPv6)               March 2006


3. ICMPv6 Error Messages

3.1.  Destination Unreachable 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             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Unused                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +                as possible without the ICMPv6 packet          +
      |                exceeding the minimum IPv6 MTU [IPv6]          |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           1

   Code           0 - No route to destination
                  1 - Communication with destination
                        administratively prohibited
                  2 - Beyond scope of source address
                  3 - Address unreachable
                  4 - Port unreachable
                  5 - Source address failed ingress/egress policy
                  6 - Reject route to destination

   Unused         This field is unused for all code values.
                  It must be initialized to zero by the originator
                  and ignored by the receiver.
   Description

   A Destination Unreachable message SHOULD be generated by a router, or
   by the IPv6 layer in the originating node, in response to a packet
   that cannot be delivered to its destination address for reasons other
   than congestion.  (An ICMPv6 message MUST NOT be generated if a
   packet is dropped due to congestion.)

   If the reason for the failure to deliver is lack of a matching entry
   in the forwarding node's routing table, the Code field is set to 0.



Conta, et al.               Standards Track                     [Page 8]

RFC 4443                 ICMPv6 (ICMP for IPv6)               March 2006


   (This error can occur only in nodes that do not hold a "default
   route" in their routing tables.)

   If the reason for the failure to deliver is administrative
   prohibition (e.g., a "firewall filter"), the Code field is set to 1.

   If the reason for the failure to deliver is that the destination is
   beyond the scope of the source address, the Code field is set to 2.
   This condition can occur only when the scope of the source address is
   smaller than the scope of the destination address (e.g., when a
   packet has a link-local source address and a global-scope destination
   address) and the packet cannot be delivered to the destination
   without leaving the scope of the source address.

   If the reason for the failure to deliver cannot be mapped to any of
   other codes, the Code field is set to 3.  Example of such cases are
   an inability to resolve the IPv6 destination address into a
   corresponding link address, or a link-specific problem of some sort.

   One specific case in which a Destination Unreachable message is sent
   with a code 3 is in response to a packet received by a router from a
   point-to-point link, destined to an address within a subnet assigned
   to that same link (other than one of the receiving router's own
   addresses).  In such a case, the packet MUST NOT be forwarded back
   onto the arrival link.

   A destination node SHOULD originate a Destination Unreachable message
   with Code 4 in response to a packet for which the transport protocol
   (e.g., UDP) has no listener, if that transport protocol has no
   alternative means to inform the sender.

   If the reason for the failure to deliver is that the packet with this
   source address is not allowed due to ingress or egress filtering
   policies, the Code field is set to 5.

   If the reason for the failure to deliver is that the route to the
   destination is a reject route, the Code field is set to 6.  This may
   occur if the router has been configured to reject all the traffic for
   a specific prefix.

   Codes 5 and 6 are more informative subsets of code 1.

   For security reasons, it is recommended that implementations SHOULD
   allow sending of ICMP destination unreachable messages to be
   disabled, preferably on a per-interface basis.






Conta, et al.               Standards Track                     [Page 9]

RFC 4443                 ICMPv6 (ICMP for IPv6)               March 2006


   Upper Layer Notification

   A node receiving the ICMPv6 Destination Unreachable message MUST
   notify the upper-layer process if the relevant process can be
   identified (see Section 2.4, (d)).

3.2.  Packet Too Big 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             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             MTU                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as possible without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           2

   Code           Set to 0 (zero) by the originator and ignored by the
                  receiver.

   MTU            The Maximum Transmission Unit of the next-hop link.

   Description

   A Packet Too Big MUST be sent by a router in response to a packet
   that it cannot forward because the packet is larger than the MTU of
   the outgoing link.  The information in this message is used as part
   of the Path MTU Discovery process [PMTU].

   Originating a Packet Too Big Message makes an exception to one of the
   rules as to when to originate an ICMPv6 error message.  Unlike other
   messages, it is sent in response to a packet received with an IPv6
   multicast destination address, or with a link-layer multicast or
   link-layer broadcast address.




Conta, et al.               Standards Track                    [Page 10]

RFC 4443                 ICMPv6 (ICMP for IPv6)               March 2006


   Upper Layer Notification

   An incoming Packet Too Big message MUST be passed to the upper-layer
   process if the relevant process can be identified (see Section 2.4,
   (d)).

3.3.  Time Exceeded 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             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Unused                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as possible without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address
                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           3

   Code           0 - Hop limit exceeded in transit
                  1 - Fragment reassembly time exceeded

   Unused         This field is unused for all code values.
                  It must be initialized to zero by the originator
                  and ignored by the receiver.

   Description

   If a router receives a packet with a Hop Limit of zero, or if a
   router decrements a packet's Hop Limit to zero, it MUST discard the
   packet and originate an ICMPv6 Time Exceeded message with Code 0 to
   the source of the packet.  This indicates either a routing loop or
   too small an initial Hop Limit value.

   An ICMPv6 Time Exceeded message with Code 1 is used to report
   fragment reassembly timeout, as specified in [IPv6, Section 4.5].





Conta, et al.               Standards Track                    [Page 11]

RFC 4443                 ICMPv6 (ICMP for IPv6)               March 2006


   Upper Layer Notification

   An incoming Time Exceeded message MUST be passed to the upper-layer
   process if the relevant process can be identified (see Section 2.4,
   (d)).

3.4.  Parameter Problem 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             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                            Pointer                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    As much of invoking packet                 |
      +               as possible without the ICMPv6 packet           +
      |               exceeding the minimum IPv6 MTU [IPv6]           |

   IPv6 Fields:

   Destination Address

                  Copied from the Source Address field of the invoking
                  packet.

   ICMPv6 Fields:

   Type           4

   Code           0 - Erroneous header field encountered
                  1 - Unrecognized Next Header type encountered
                  2 - Unrecognized IPv6 option encountered

   Pointer        Identifies the octet offset within the
                  invoking packet where the error was detected.

                  The pointer will point beyond the end of the ICMPv6
                  packet if the field in error is beyond what can fit
                  in the maximum size of an ICMPv6 error message.