Internet DRAFT - draft-herbert-ipv6-update-dest-ops
draft-herbert-ipv6-update-dest-ops
INTERNET-DRAFT Tom Herbert
Intended Status: Informational Quantonium
Expires: February 18, 2019
August 17, 2018
Updates to Destination Options Processing
draft-herbert-ipv6-update-dest-ops-00
Abstract
This document updates the requirements for processing Destination
Options in IPv6 in two ways. First, the requirement that all
intermediate destinations in a Routing header must process options in
a Destination header appearing before the Routing header is relaxed.
Secondly, the processing of a Destination Option marked as changeable
is clarified.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Processing Requirements of Destination Options . . . . . . . . 3
3 Changeable Destination Options . . . . . . . . . . . . . . . . 4
4 Security Considerations . . . . . . . . . . . . . . . . . . . . 4
5 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
6 References . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1 Normative References . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5
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1 Introduction
[RFC8200] specifies the Destination Options header and processing
requirements. Two requirements for processing Destination Options are
described based on their association with a Routing header. A
Destination Options header that is in a packet with no Routing
header, or follows a Routing header, is processed only by the final
destination node (if no routing header is present that is simply the
destination of the packet). A Destination Options header that comes
before a Routing header must be processed by each intermediate
destination listed in a Routing header. In the first case,
Destination Options are only processed by one node, but in the latter
they may need to be processed by many intermediate nodes. This
distinction motivates a couple of clarifications to the requirements.
In that case of Destination Options that come before a Routing
header, this document proposes that intermediate destination nodes
may ignore the options. This change has a similar justification for
relaxing the requirement that all intermediate nodes process Hop-by-
Hop options in [RFC8200]. Intermediate destination nodes may be
closer in taxonomy to switches and routers than end hosts, so it
follows that they may have similar processing constraints in
efficiently processing extension headers and TLVs. Those constraints
could lead to similar ad hoc implementation behaviors for processing
packets with options. Some implementations have dropped packets with
options, others have relegated them to slow path processing; in
either case, these behaviors at even a few nodes can essentially
render options unusable. Allowing intermediate nodes to ignore
options retains the primary value and usability of Destination
Options. Intermediate nodes that are not interested in them can
ignore them, nodes that fully support them can process them.
Destination Options may be marked as changeable (the third-highest-
order bit of the Option Type for the Destination Option is set). Per
[RFC8200], for such a marked option its Option Data may be changed en
route. [RFC8200] also states that with the exception of Hop-by-Hop
options, extension headers are not processed except by a destination.
It follows that the only possible case that a Destination Option may
be modified en route is when an intermediate destination in a Routing
header modifies it. This document clarifies that.
2 Processing Requirements of Destination Options
Options in a Destination Options header that is after a Routing
header, or are in a packet with no Routing header present, MUST be
examined and processed by the destination node.
The options in a Destination Options header that appears before a
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Routing header MAY be examined or processed by intermediate nodes
listed in the routing header, including the original destination as
well as the ultimate destination provided in the routing header. If
an intermediate node does not process the options in a Destination
Option header appearing before a Routing header, then it MUST skip
over the Destination Options header and continue to process the next
header which should be a Routing header.
3 Changeable Destination Options
If a Destination Option in a Destination Options header that appears
before a Routing header is marked as changeable (the third-highest
order bit of the option type is set), then the Option Data may be
changed by an intermediate destination node en route to the final
destination. Specifically, the node for the initial destination
address as well as any intermediate node listed in the Routing header
may change the Option Data.
If a Destination Option is marked to be changeable (the third-highest
order bit of the option type is set) and is in a Destination Options
header that follows a Routing header, or there is no Routing header
present, then the Option Data cannot be changed en route. There are
no nodes in the path that are permitted to change the Option Data.
Note that the requirement when an Authentication header is present
that the entire Option Data field must be treated as zero-valued
octets when computing or verifying the packet's authenticating value
is still applicable.
4 Security Considerations
Relaxing the requirement that Destination Options can be ignored by
intermediate nodes should not pose any new security risk. It should
be noted that any security mechanism specified in a Destination
Option should take into account that not all intermediate
destinations would necessarily process the security option.
5 IANA Considerations
There are no IANA considerations in this specification.
6 References
6.1 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>.
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Author's Address
Tom Herbert
Quantonium
Santa Clara, CA
USA
Email: tom@quantonium.net
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