Network Working Group Z. Li
Internet-Draft S. Peng
Intended status: Standards Track Huawei
Expires: January 4, 2021 July 3, 2020
Hop-by-Hop Forwarding Options Header
draft-li-6man-hbh-fwd-hdr-00
Abstract
RFC8200 specifies the HBH header that is assumed to be processed by
each hop in the delivery path of the packet. However, RFC8200 also
expects that nodes processing the HBH header have been explicitly
configured to do so. Therefore, it cannot be assumed that a HBH
header present in the packet is processed. It all depends on the
configuration of each node across the path. Moreover, in most of
networks today, the processing of the HBH header is done in the
control plane (slow processing path) which incurs several limitations
among which resources consumption and security risk.
For these reasons, over time, the Hop-by-Hop Options header has been
sparsely used without any form of large scale deployment. Also, most
of already defined HBH options are forwarding options which contain
forwarding plane information that needs not to be sent to the control
plane.
This document proposes a new Hop-by-Hop Forwarding Options Header in
order to carry Hop-by-Hop options that are solely intended to and
processed by the forwarding plane. This new HBH header is confined
in and dedicated to the forwarding plane while the current HBH header
can still be used for control plane options.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on January 4, 2021.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Problem Statement and Motivation . . . . . . . . . . . . . . 4
2.1. Specifications in RFC8200 . . . . . . . . . . . . . . . . 4
2.2. Classification of HBH Options . . . . . . . . . . . . . . 5
2.3. Service Requirements . . . . . . . . . . . . . . . . . . 5
3. Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Hop-by-Hop Forwarding Options Header . . . . . . . . . . 6
3.2. The usage of the existing Hop-by-Hop Options Header . . . 7
4. Security Considerations . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Appendix. Existing HBH Options . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
As specified in [RFC8200], the Hop-by-Hop (HBH) Options header is
used to carry optional information that will be examined and
processed by every node along a packet's delivery path if it is
explicitly configured to do so. Since there is no specification on
the possible configuration, nodes may be configured to ignore the
Hop-by-Hop Options header, drop packets containing a Hop-by-Hop
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Options header, or assign packets containing a Hop-by-Hop Options
header to a slow processing path. [RFC6564] shows the Reports from
the field indicating that some IP routers deployed within the global
Internet are configured either to ignore or to drop packets having a
hop-by-hop header. As stated in [RFC7872], many network operators
perceive HBH Options to be a breach of the separation between the
forwarding and control planes. Therefore, several network operators
configured their nodes so to discard all packets containing the HBH
Options Extension Header, while others configured nodes to forward
the packet but to ignore the HBH Options. [RFC7045] also states that
hop-by-hop options are not handled by many high-speed routers or are
processed only on a slow path.
Generally, modern routers maintain the separation between forwarding
plane and control plane with plentiful forwarding plane resource but
constrained control plane resource. In order to protect the control
plane, policies are enforced in order to restrict access from the
forwarding plane to the control plane. Some operators severely rate-
limit packets containing the HBH Options Extension Header when they
are being sent to the control plane which will cause packet drops.
The Hop-by-Hop Options can be categorized into Hop-by-Hop Forwarding
Options and Hop-by-Hop Control Options, which contains information
for the forwarding plane and the control plane of the nodes,
respectively. It is necessary and required to separate the two types
of Hop-by-Hop options since they require different process
procedures. The packets carrying the Hop-by-Hop Forwarding Options
are supposed to be maintained in the forwarding plane while the
packets carrying the Hop-by-Hop Control Options are supposed to be
sent to the control plane. The current Hop-by-Hop Options header
specified in [RFC8200] is used to carry both types of Hop-by-Hop
options, and there is no way or indicator to separate the processing
of the two kinds of Hop-by-Hop options using the current
specifications in [RFC8200].
In the current networks, the common implementation is to send all
packets containing a HBH header to the control plane even if they
contain only pad options (a forwarding option specified in
[RFC8200]), resulting in various possible effects such as a risk of a
DoS attack on the router, inconsistent drops among those packets due
to rate limiting, or other effects. This will impact the normal end-
to-end IP forwarding of the network services.
Therefore, due to these limitations, the HBH header has seen limited
use and deployments, and protocol designers are recommended to avoid
using hop-by-hop options in any new protocols. However, there have
been over ten HBH options already specified in RFCs as listed in
Appendix and the specified Forwarding Options are in the majority.
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Moreover, as IPv6 is being rapidly and widely deployed worldwide,
more and more new services that requires hop-by-hop forwarding
process behavior are emerging such as IOAM with IPv6 encapsulation
[draft-ietf-ippm-ioam-ipv6-options]. Therefore, these requirements
should be addressed urgently and properly by the use of an efficient
HBH header when processed in the forwarding plane by transit nodes.
This document proposes a Hop-by-Hop Forwarding Options header to
carry the Hop-by-Hop forwarding options while the existing Hop-by-Hop
Options header is used to carry the Hop-by-Hop control options only.
2. Problem Statement and Motivation
This section describes the problem statement and motivation for
defining a new Hop-by-Hop Forwarding Options header.
2.1. Specifications in RFC8200
While [RFC2460] required that all nodes must examine and process the
Hop-by-Hop Options header, with [RFC8200] it is expected that nodes
along a packet's delivery path only examine and process the Hop-by-
Hop Options header if explicitly configured to do so. The
configuration of the node determines the HBH processing behavior in
the node which implies that each node may have a different behavior
than the others. As specified in [RFC8200], nodes may be configured
to ignore the Hop-by-Hop Options header or drop packets containing a
Hop-by-Hop Options header or assign packets containing a Hop-by-Hop
Options header to a slow processing path. These various behaviors
are observed and described in specifications such as [RFC7045] and
[RFC7872]. Due to such behaviors, new hop-by-hop options are not
recommended in [RFC8200] hence the usability of HBH options is
severely limited.
The Hop-by-Hop Options header is identified by a Next Header value of
zero in the IPv6 header. Currently, the behaviors performed by the
nodes on the packets containing a Hop-by-Hop Options header is only
based on the value of this Next Header in the IPv6 header, that is,
the value of the Next Header is the only trigger for the behaviors to
be performed.
In current networks, usually, nodes are configured in order to assign
packets containing a Hop-by-Hop Options header (indicated by the Next
Header = 0) to a slow processing path, i.e. to the control plane of
the nodes. Very often, such configuration is embedded in the
implementation of the node and cannot be changed or reconfigured.
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2.2. Classification of HBH Options
The Hop-by-Hop Options header contains one or more Hop-by-Hop
Options. Each HBH Option contains a type identifier, i.e. Option
Type. The Hop-by-Hop Options can be categorized into two types: HBH
Forwarding Options and HBH Control Options. The HBH forward options
contain information that is useful to a router's forwarding plane,
e.g. the Jumbo Payload Option [RFC2675]. While the HBH Control
Options contain information that is useful to a router's control
plane, e.g. the Router Alert Option [RFC2711]. Currently, both HBH
forwarding and control options are carried in the same HBH Options
header. There is no specification defining rules for differentiating
the process of the two kinds of options.
According to the common configuration in the current networks, i.e.
to assign packets containing a Hop-by-Hop Options header (indicated
by the Next Header = 0) to a slow processing path, all the HBH
Options will be sent to the control plane of the nodes. It impacts
the normal IP forwarding procedure of the packets containing the HBH
forwarding options which should be processed in the forwarding plane.
As stated above, it also introduces a severe risk of DoS attacks
using HBH headers.
If all the HBH Options are forced to be processed first in the
forwarding plane and then classified according to the HBH Option
Type, it requires the consumption of the forwarding plane resources
to make such processing selection, which will impact the forwarding
efficiency. Moreover, there are some existing nodes that are
configured to assign the packets containing a Hop-by-Hop Options
header to the control plane of the nodes cannot be reconfigured.
Appendix of this document provides the classification of the
currently defined HBH options into HBH forwarding options and HBH
control options, and the HBH forwarding options are in the majority.
2.3. Service Requirements
As listed in the Appendix, there have been over ten HBH options
already specified in RFCs and the specified forwarding options are in
the majority. As IPv6 is being rapidly and widely deployed
worldwide, more and more applications and network services are
migrating to or adopting IPv6. More and more new services that
requires hop-by-hop forwarding process behavior are emerging and the
HBH Options header is going to be utilized by new services in various
use scenarios.
As more services start utilizing the HBH Options header, more packets
containing HBH Options are going to be injected into the networks.
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According to the current common configuration in most network
deployments, all the packets of the new services are going to be sent
to the control plane of the nodes, with the possible consequence of
causing a DoS effect on the control plane. The packets will be
dropped and the normal IP forwarding may be severely impacted. The
deployment of new network services involving multi-vendor
interoperability will become impossible.
In-situ OAM with IPv6 encapsulation [draft-ietf-ippm-ioam-
ipv6-options] is one of the examples. IOAM in IPv6 is used to
enhance diagnostics of IPv6 networks and complements other
mechanisms, such as the IPv6 Performance and Diagnostic Metrics
Destination Option described in [RFC8250]. The IOAM data fields are
encapsulated in "option data" fields of the Hop-by-Hop Options header
if Pre-allocated Tracing Option, Incremental Tracing Option, or Proof
of Transit Option are carried [I-D.ietf-ippm-ioam-data], that is, the
IOAM performs per hop.
As above mentioned, according to the current common configuration,
all the packets employing IOAM are going to be sent to the control
plane of every node along the path, it will cause a severe effect DoS
on the control plane. The packets will be inconsistently dropped and
the normal IP forwarding will be severely impacted. The end-to-end
deployment of IOAM in a network involving nodes from multiple vendors
is impossible.
3. Proposal
3.1. Hop-by-Hop Forwarding Options Header
We propose to define a new HBH Forwarding Options header dedicated to
carry the HBH Forwarding Options. The IPv6 packets containing this
Hop-by-Hop Forwarding Options header will be only processed in the
forwarding plane and MUST NOT be sent to the control plane of the
network nodes.
The Hop-by-Hop Forwarding Options header is identified by a Next
Header value of TBD in the IPv6 header and has the following format:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. HBH Forwarding Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the Hop-by-Hop
Forwarding Options header.
Hdr Ext Len 8-bit unsigned integer. Length of the
Hop-by-Hop Forwarding Options header in 8-octet
units, not including the first 8 octets.
Options Variable-length field, of length such that the
complete Hop-by-Hop Options header is an
integer multiple of 8 octets long. Contains
one or more TLV-encoded HBH forwarding options.
The Hop-by-Hop Forwarding Options header is recommended to be placed
immediately after the IPv6 header.
The Hop-by-Hop Forwarding Options follows the formatting guidelines
specified in the Appendix A. of [RFC8200].
3.2. The usage of the existing Hop-by-Hop Options Header
The existing Hop-by-Hop Options Header, identified by a Next Header
value of zero in the IPv6 header, can still be used for carrying the
HBH control options. The IPv6 packets carrying such HBH control
options will be sent to the control plane anyway, so it follows the
exact current processing procedures.
4. Security Considerations
It is the same as the Security Considerations in [RFC8200] for the
part related with the HBH Options header.
5. IANA Considerations
TBD: Next Header for Hop-by-Hop Forwarding Options Header
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6. Appendix. Existing HBH Options
We further classify the HBH Options into HBH Forwarding and HBH
Control Options. We can see that among all the defined HBH Options
the HBH Forwarding Options are in the majority.
HBH Forwarding Options:
o PAD Options: PAD1 and PADn [RFC8200]
o Jumbo Payload [RFC2675]
o RPL Option [RFC6553]
o Common Architecture Label 1Pv6 Security Option [RFC5570]
o SMF Option [RFC6621]
o MPL Option [RFC7731]
o DFF Option [RFC6971]
o MTU Option [I-D.ietf-6man-mtu-option]
o AltMark Option [I-D.ietf-6man-ipv6-alt-mark]
HBH Control Options:
o Router Alert Option [RFC2711]
o Quickstart Option [RFC4782]
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<https://www.rfc-editor.org/info/rfc7045>.
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[RFC7872] Gont, F., Linkova, J., Chown, T., and W. Liu,
"Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>.
[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>.
7.2. Informative References
[I-D.ietf-6man-ipv6-alt-mark]
Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
Pang, "IPv6 Application of the Alternate Marking Method",
draft-ietf-6man-ipv6-alt-mark-01 (work in progress), June
2020.
[I-D.ietf-6man-mtu-option]
Hinden, R. and G. Fairhurst, "IPv6 Minimum Path MTU Hop-
by-Hop Option", draft-ietf-6man-mtu-option-02 (work in
progress), March 2020.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, DOI 10.17487/RFC2711, October 1999,
<https://www.rfc-editor.org/info/rfc2711>.
[RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
Start for TCP and IP", RFC 4782, DOI 10.17487/RFC4782,
January 2007, <https://www.rfc-editor.org/info/rfc4782>.
[RFC5570] StJohns, M., Atkinson, R., and G. Thomas, "Common
Architecture Label IPv6 Security Option (CALIPSO)",
RFC 5570, DOI 10.17487/RFC5570, July 2009,
<https://www.rfc-editor.org/info/rfc5570>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
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[RFC6621] Macker, J., Ed., "Simplified Multicast Forwarding",
RFC 6621, DOI 10.17487/RFC6621, May 2012,
<https://www.rfc-editor.org/info/rfc6621>.
[RFC6971] Herberg, U., Ed., Cardenas, A., Iwao, T., Dow, M., and S.
Cespedes, "Depth-First Forwarding (DFF) in Unreliable
Networks", RFC 6971, DOI 10.17487/RFC6971, June 2013,
<https://www.rfc-editor.org/info/rfc6971>.
[RFC7731] Hui, J. and R. Kelsey, "Multicast Protocol for Low-Power
and Lossy Networks (MPL)", RFC 7731, DOI 10.17487/RFC7731,
February 2016, <https://www.rfc-editor.org/info/rfc7731>.
Authors' Addresses
Zhenbin Li
Huawei
Beijing 100095
China
Email: lizhenbin@huawei.com
Shuping Peng
Huawei
Beijing 100095
China
Email: pengshuping@huawei.com
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