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INTERNET-DRAFT                                                T. Herbert
Intended Status: Standard                                     Quantonium
Expires: June 2018

                                                       December 27, 2017


     ICMPv6 errors for discarding packets due to processing limits
                   draft-herbert-6man-icmp-limits-02


Abstract

   Network nodes may discard packets if they are unable to process
   protocol headers of packets due to processing constraints or limits.
   When such packets are dropped, the sender receives no indication so
   it cannot take action to address the cause of discarded packets. This
   document defines ICMP errors that can be sent by a node that discards
   packets because it is unable to process the protocol headers. A node
   that receives such an ICMP error may be able to modify what it sends
   in future packets to avoid subsequent packet discards.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

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Copyright and License Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.



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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1 Extension header limits  . . . . . . . . . . . . . . . . . .  3
     1.2 Aggregate header limits  . . . . . . . . . . . . . . . . . .  4
   2  ICMP errors for extension header limits . . . . . . . . . . . .  4
     2.1 Format . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2 Unrecognized Next Header type encountered (code 1) . . . . .  5
     2.3 Extension header too big (code 4)  . . . . . . . . . . . . .  5
     2.4 Extension header chain too long (code 5) . . . . . . . . . .  6
     2.5 Too many options in extension header (code 6)  . . . . . . .  6
   3  ICMP error for aggregate header limits  . . . . . . . . . . . .  6
     3.1 Format . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2 Usage  . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4  Operation . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1 Priority of reporting  . . . . . . . . . . . . . . . . . . .  8
     4.2 Host response  . . . . . . . . . . . . . . . . . . . . . . .  8
   5  Security Considerations . . . . . . . . . . . . . . . . . . . .  9
   6  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
     6.1 Parameter Problem codes  . . . . . . . . . . . . . . . . . . 10
     6.2 Destination Unreachable codes  . . . . . . . . . . . . . . . 10
   7  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1  Normative References  . . . . . . . . . . . . . . . . . . . 10
     7.2  Informative References  . . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10















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1  Introduction

   This document specifies ICMP errors that can be sent when a node
   discards a packet due to it being unable to process the necessary
   protocol headers because of processing constraints or limits.

   Four of the errors are specific to processing limits of extension
   headers; another error is used when the aggregate protocol headers in
   a packet exceed the processing limits of a node.

1.1 Extension header limits

   With IPv6, optional internet-layer information is carried in one or
   more IPv6 Extension Headers [RFC8200]. Extension Headers are placed
   between the IPv6 header and the Upper-Layer Header in a packet.  The
   term "Header Chain" refers collectively to the IPv6 header, Extension
   Headers, and Upper-Layer Headers occurring in a packet. Individual
   extension headers may have a length of 2048 and must fit into one
   MTU. Destination Options and Hop by Hop Options contain a list
   options in Type-length-value (TLV) format. Each option includes a
   length of the data field in octets and the minimum size of an option
   (non-pad type) is two bytes and the maximum length is 257 bytes. The
   number of options in an extension header is only limited by the
   length of the extension header and MTU. Options may also be skipped
   over by a receiver if they are unknown and the Option Type indicates
   to skip (first two bits are 00).

   Per [RFC8200], except for Hop by Hop options, extension headers are
   not examined or processed by intermediate nodes. Many intermediate
   nodes, however, do examine extension header for various purposes. For
   instance, a node may examine all extension headers to locate the
   transport header of packet in order to implement transport layer
   filtering or to track connections to implement a stateful firewall.

   Destination hosts are expected to process all extensions headers and
   options in Hop by Hop and Destination Options.

   Due to the variable lengths, high limits of lengths of extension
   headers, or potential for Denial of Service attack; many devices
   impose operational limits of extension headers in packets they can
   process. [RFC7045] discusses the requirements of intermediate nodes
   that discard packets because of unrecognized extension headers. When
   a limit is exceeded, the typical behavior is to silently discard a
   packet. The limits are non-standard and may be configurable per
   implementation. Both intermediate nodes and end hosts may institute
   such limits on extension header processing.

   This document defines three Parameter Problem codes and extends the



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   applicably of an existing code that are sent by a node that discards
   a packet due to processing limits of extension headers being
   exceeded. A source host that receives an ICMP error can modify the
   use of extension headers in subsequent packets to the destination in
   order to avoid further occurrences of packets being discarded.

1.2 Aggregate header limits

   Many hardware devices implement a parsing buffer of a fixed sized to
   process packets. The parsing buffer is expected to contain all the
   headers (often up to a transport layer header for filtering) that a
   device needs to examine. Parsing buffers have been implemented with
   various sizes (512 bytes is common, some devices have smaller sizes).

   When the aggregate length of headers in a packet exceeds the size of
   the parsing buffer, a device will typically either discard the packet
   or defer processing to a software slow path. In either case, no
   indication of a problem is sent back to the sender.

   This document defines one code for ICMPv6 Destination Unreachable
   that is sent by a node that is unable to process the headers of a
   packet due to the aggregate size of the packet headers exceeding a
   processing limit (e.g. exceeding the size of a parsing buffer). A
   source host that receives an ICMP error can modify the headers used
   in subsequent packets to try to avoid further occurrences of packets
   being discarded or relegated to a slow path.

2  ICMP errors for extension header limits

   Three new codes are defined for Parameter Problem type and
   applicability of one existing code is extended for ICMP errors for
   extension header limits.

2.1 Format

   The format of the ICMP message for an extension header limit exceeded
   error is:

    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]           |



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   IPv6 Fields:

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

   ICMPv6 Fields:

      Type
         4 (Parameter Problem type)

      Code (pertinent to this specification)
         1 - Unrecognized Next Header type encountered
         4 - Extension header too big
         5 - Extension header chain too long
         6 - Too many options in extension header

      Pointer
         Identifies the octet offset within the invoking packet where
         the problem occurred.

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

2.2 Unrecognized Next Header type encountered (code 1)

   [RFC8200] specifies that a destination host should send an
   "unrecognized next header type" when a Next Header value is
   unrecognized in a packet. This document extends this to allow
   intermediate nodes to send this same error for a packet that is
   discarded because a node does not recognize a Next Header type.

   This code SHOULD be sent by an intermediate node that discards a
   packet because it encounters a Next Header type that is unknown in
   its examination. The ICMP Pointer field is set to the offset of the
   unrecognized value within the original packet.

   Note that when the original sender receives the ICMP error it can
   differentiate between the message being sent by a destination host,
   per [RFC4443], and an error sent by an intermediate host based on
   matching the source address of the ICMP packet and the destination
   address of the packet in the ICMP data.

2.3 Extension header too big (code 4)

   An ICMP Parameter Problem with code for "extension header too big"
   SHOULD be sent when a node discards a packet because the size of an
   extension header exceeds its processing limit. The ICMP Pointer field



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   is set to the offset of the first octet in the extension header that
   exceeds the limit.

2.4 Extension header chain too long (code 5)

   An ICMP Parameter Problem with code for "extension header chain too
   long" SHOULD be sent when a node discards a packet with an extension
   header chain because an extension header chains exceeds it processing
   limit.

   There are two different limits that might be applied: a limit on the
   total size in octets of the header chain, and a limit on the number
   of extension headers in the chain. This error code is used in both
   cases. In the case that the a size limit is exceeded, the ICMP
   Pointer is set to first octet beyond the limit. In the case that the
   number of extension headers is exceeded, the ICMP Pointer is set to
   the offset of first octet of the first extension header that is
   beyond the limit.

2.5 Too many options in extension header (code 6)

   An ICMP Parameter Problem with code for "too many options in
   extension header" SHOULD be sent when a node discards a packet with
   an extension header that has a number of options that exceed the
   processing limits of the node. This code is applicable for
   Destination options or Hop by Hop options. The ICMP Pointer field is
   set to the first octet of the first option that exceeds the limit.

3  ICMP error for aggregate header limits

   One code is defined for Destination Unreach type for aggregate header
   limits.

3.1 Format

   The error for aggregate header limits employs a multi-part ICMP
   message format as defined in [RFC4884]. The extended structure
   contains a pointer to the octet beyond the limit.

   The format of the ICMP message for an aggregate header limit exceeded
   is:










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   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    |    Length     |             unused            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Internet Header + leading octets of original datagram    |
   |                                                               |
   |                           //                                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                            Pointer                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   IPv6 Fields:

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

   ICMPv6 Fields:

      Type
         1 (Destination Unreachable type)

      Code (pertinent to this specification)
         8 - Headers too long

      Length
         Length of the "original datagram" measured in 64 bit words

      Pointer
         Identifies the octet offset within the invoking packet where a
         limit was exceeded.

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

3.2 Usage

   An ICMP Destination Unreachable error with code for "headers too
   long" SHOULD be sent when a node discards a packet because the
   aggregate length of headers in the packet exceeds the processing
   limits of the node. The Pointer in the extended ICMP structure is set
   to the offset of the first octet that exceeds the limit.




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4  Operation

   Nodes that send or receive ICMP errors due to header processing
   limits MUST generally comply with ICMP processing as specified in
   [RFC4443].

4.1 Priority of reporting

   More than one ICMP error may be applicable to report for a packet.
   For instance, the number of extension headers in a packet might
   exceed a limit and the aggregate length of protocol headers might
   also exceed a limit. Only one ICMP error should be sent for a packet,
   so a priority is defined to determine which error to report.

   The reporting priority of ICMP errors for processing limits is from
   highest to lowest priority:

      1) Real error (existing codes)

      2) Unrecognized Next Header type encountered by an intermediate
         node

      3) Too many options in an extension header

      4) Extension header too big

      5) Extension header chain too long for number of extension headers
         limit exceeded

      6) Extension header chain too long for size of the extension
         header chain exceeding a limit

      7) Headers too long

4.2 Host response

   When a source host receives an ICMP error for a processing limit
   being exceeded, it SHOULD verify the ICMP error is valid and take an
   appropriate action.

   The ICMP error SHOULD be logged with sufficient detail for debugging
   packet loss. The details of the error, including the addresses and
   the offending extension header or data, should be retained. This
   would be useful for instance to debug when a node is mis-configured
   and unexpectedly discarding packets, or when a new extension header
   is being deployed.

   A host MAY modify its usage of protocol headers in subsequent packets



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   to avoid repeated occurrences of the same error.

   For ICMP errors cause by extension header limits being exceeded:

      * An error SHOULD be reported to an application if the application
        enabled extension headers for its traffic. The application MAY
        either terminate a connection if extension headers are required,
        stop using extension headers in packets to the destination
        indicated in packet of the ICMP error, or attempt modify its use
        of extension headers or headers to avoid the packet drop.

      * A host system SHOULD take action if it is automatically
        inserting extension headers into packets unbeknownst to the
        application. The host system SHOULD either stop using extension
        headers or modify its used of extension headers for subsequent
        packets sent to the destination indicated in the packet of the
        ICMP error.

5  Security Considerations

   This document does not introduce any new security concerns for use of
   ICMP errors. The security considerations for ICMPv6 described in
   [RFC4443] are applicable.




























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6  IANA Considerations

6.1 Parameter Problem codes

   IANA is requested to assign the following codes for ICMPv6 type 4
   "Parameter Problem":

         4 - Extension header too big

         5 - Extension header chain too long

         6 - Too many options in extension header

6.2 Destination Unreachable codes

   IANA is requested to assign the following codes for ICMPv6 type 1
   "Destination Unreachable":

         8 - Headers too long

7  References

7.1  Normative References

   [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
             (IPv6) Specification", STD 86, RFC 8200, DOI
             10.17487/RFC8200, July 2017, <https://www.rfc-
             editor.org/info/rfc8200>.

   [RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing of
             IPv6 Extension Headers", RFC 7045, DOI 10.17487/RFC7045,
             December 2013, <http://www.rfc-editor.org/info/rfc7045>.

   [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
             Control Message Protocol (ICMPv6) for the Internet Protocol
             Version 6 (IPv6) Specification", RFC 4443, DOI
             10.17487/RFC4443, March 2006, <http://www.rfc-
             editor.org/info/rfc4443>.

   [RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
             "Extended ICMP to Support Multi-Part Messages", RFC 4884,
             DOI 10.17487/RFC4884, April 2007, <https://www.rfc-
             editor.org/info/rfc4884>.
7.2  Informative References


Author's Address




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   Tom Herbert
   Quantonium
   Santa Clara, CA
   USA


   Email: tom@herbertland.com












































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