Internet DRAFT - draft-herbert-6man-icmp-limits
draft-herbert-6man-icmp-limits
INTERNET-DRAFT T. Herbert
Intended Status: Standard Quantonium
Expires: July 2018
January 15, 2018
ICMPv6 errors for discarding packets due to processing limits
draft-herbert-6man-icmp-limits-03
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 ICMPv6 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 ICMPv6 error may be able to
modify what it sends in future packets to avoid subsequent packet
discards.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Extension header limits . . . . . . . . . . . . . . . . . . 3
1.2 Aggregate header limits . . . . . . . . . . . . . . . . . . 4
2 ICMPv6 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 ICMPv6 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
8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 10
7 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1 Normative References . . . . . . . . . . . . . . . . . . . 10
7.2 Informative References . . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
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1 Introduction
This document specifies ICMPv6 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. New
ICMPv6 code points are defined as an update to [RFC4443].
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.
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This document defines three Parameter Problem codes and extends the
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 ICMPv6 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 ICMPv6 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 ICMPv6 errors for extension header limits
Three new codes are defined for Parameter Problem type and
applicability of one existing code is extended for ICMPv6 errors for
extension header limits.
2.1 Format
The format of the ICMPv6 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 +
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| exceeding the minimum IPv6 MTU [IPv6] |
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 ICMPv6 Pointer field is set to the offset of the
unrecognized value within the original packet.
Note that when the original sender receives the ICMPv6 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 ICMPv6 packet and the destination
address of the packet in the ICMPv6 data.
2.3 Extension header too big (code 4)
An ICMPv6 Parameter Problem with code for "extension header too big"
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SHOULD be sent when a node discards a packet because the size of an
extension header exceeds its processing limit. The ICMPv6 Pointer
field 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 ICMPv6 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 ICMPv6
Pointer is set to first octet beyond the limit. In the case that the
number of extension headers is exceeded, the ICMPv6 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 ICMPv6 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 ICMPv6 Pointer field
is set to the first octet of the first option that exceeds the limit.
3 ICMPv6 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 ICMPv6
message format as defined in [RFC4884]. The extended structure
contains a pointer to the octet beyond the limit.
The format of the ICMPv6 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 ICMPv6 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 ICMPv6 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 ICMPv6 errors due to header processing
limits MUST generally comply with ICMPv6 processing as specified in
[RFC4443].
4.1 Priority of reporting
More than one ICMPv6 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 ICMPv6 error should be sent for a
packet, so a priority is defined to determine which error to report.
The reporting priority of ICMPv6 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 ICMPv6 error for a processing limit
being exceeded, it SHOULD verify the ICMPv6 error is valid and take
an appropriate action.
The ICMPv6 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 ICMPv6 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 ICMPv6 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
ICMPv6 error.
5 Security Considerations
This document does not introduce any new security concerns for use of
ICMPv6 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
8 Acknowledgments
The authors would like to thank Ron Bonica, Bob Hinden for their
comments and suggestions that improved this document.
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>.
[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>.
[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>.
[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>.
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7.2 Informative References
Author's Address
Tom Herbert
Quantonium
Santa Clara, CA
USA
Email: tom@herbertland.com
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