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IETF RFC 5350
IANA Considerations for the IPv4 and IPv6 Router Alert Options
Last modified on Thursday, September 11th, 2008
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Network Working Group J. Manner
Request for Comments: 5350 TKK
Updates: 2113, 3175 A. McDonald
Category: Standards Track Siemens/Roke
September 2008
IANA Considerations for the IPv4 and IPv6 Router Alert Options
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The IETF Trust (2008).
Abstract
This document updates the IANA allocation rules and registry of IPv4
and IPv6 Router Alert Option Values.
Table of Contents
1. Introduction ....................................................2
2. Use of the Router Alert Option Value Field ......................2
3. IANA Considerations .............................................4
3.1. IANA Considerations for IPv4 Router Alert Option Values ....4
3.2. IANA Considerations for IPv6 Router Alert Option Values ....5
4. Security Considerations .........................................5
5. Acknowledgements ................................................6
6. References ......................................................6
6.1. Normative References .......................................6
6.2. Informative References .....................................6
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RFC 5350 IANA Considerations for Router Alert September 2008
1. Introduction
The IP Router Alert Option is defined for IPv4 in [RFC 2113]. A
similar IPv6 option is defined in [RFC 2711]. When one of these
options is present in an IP datagram, it indicates that the contents
of the datagram may be interesting to routers. The Router Alert
Option (RAO) is used by protocols such as the Resource Reservation
Protocol (RSVP) [RFC 2205] and IGMP [RFC 3376].
Both the IPv4 and IPv6 options contain a two-octet Value field to
carry extra information. This information can be used, for example,
by routers to determine whether or not the packet should be more
closely examined by them.
There can be up to 65536 values for the RAO. Yet, currently there is
only a registry for IPv6 values. No registry or allocation policies
are defined for IPv4.
This document updates the IANA registry for managing IPv4 and IPv6
Router Alert Option Values, and removes one existing IPv6 Router
Alert Option Value.
2. Use of the Router Alert Option Value Field
One difference between the specifications for the IPv4 and IPv6
Router Alert Options is the way values for the Value field are
managed. In [RFC 2113], the IPv4 Router Alert Option Value field has
the value 0 assigned to "Router shall examine packet". All other
values (1-65535) are reserved. Neither a management mechanism (e.g.,
an IANA registry) nor an allocation policy are provided for the IPv4
RAO values.
The IPv6 Router Alert Option has an IANA-managed registry
[IANA-IPv6RAO] containing allocations for the Value field.
In [RFC 3175], the IPv4 Router Alert Option Value is described as a
parameter that provides "additional information" to the router in
making its interception decision, rather than as a registry managed
by IANA. As such, this aggregation mechanism makes use of the Value
field to carry the reservation aggregation level. For the IPv6
option, IANA has assigned a set of 32 values to indicate reservation
levels. However, since other registrations have already been made in
that registry, these values are from 3-35 (which is actually a set of
33 values).
Although it might have been desirable to have the same values used in
both the IPv4 and IPv6 registries, the initial allocations in
[RFC 2711] and the aggregation-level allocations in [RFC 3175] have
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RFC 5350 IANA Considerations for Router Alert September 2008
made this impossible. The following table shows the allocations in
the IPv6 registry and the values used in the IPv4 registry, where the
latter have been deduced from [RFC 2113] and [RFC 3175] with the
assumption that the number of aggregation levels can be limited to 32
as in the IPv6 case. Entries for values 6 to 31 have been elided for
brevity.
+----------+-------------------------+------------------------------+
| Value | IPv4 RAO Meaning | IPv6 RAO Meaning |
+----------+-------------------------+------------------------------+
| 0 | Router shall examine | Datagram contains a |
| | packet [RFC 2113] | Multicast Listener Discovery |
| | [RFC 2205] [RFC 3376] | message [RFC 2711] [RFC 2710] |
| | [RFC 4286] | [RFC 4286] |
| 1 | Aggregated Reservation | Datagram contains RSVP |
| | Nesting Level 1 | message [RFC 2711] [RFC 2205] |
| | [RFC 3175] | |
| 2 | Aggregated Reservation | Datagram contains an Active |
| | Nesting Level 2 | Networks message [RFC 2711] |
| | [RFC 3175] | [Schwartz2000] |
| 3 | Aggregated Reservation | Aggregated Reservation |
| | Nesting Level 3 | Nesting Level 0 [RFC 3175](*) |
| | [RFC 3175] | |
| 4 | Aggregated Reservation | Aggregated Reservation |
| | Nesting Level 4 | Nesting Level 1 [RFC 3175] |
| | [RFC 3175] | |
| 5 | Aggregated Reservation | Aggregated Reservation |
| | Nesting Level 5 | Nesting Level 2 [RFC 3175] |
| | [RFC 3175] | |
| ... | ... | ... |
| 32 | Aggregated Reservation | Aggregated Reservation |
| | Nesting Level 32 | Nesting Level 29 [RFC 3175] |
| | [RFC 3175] | |
| 33 | Reserved | Aggregated Reservation |
| | | Nesting Level 30 [RFC 3175] |
| 34 | Reserved | Aggregated Reservation |
| | | Nesting Level 31 [RFC 3175] |
| 35 | Reserved | Aggregated Reservation |
| | | Nesting Level 32(*) |
| | | [RFC 3175] |
| 36-65534 | Reserved | Reserved to IANA for future |
| | | assignment |
| 65535 | Reserved | Reserved [IANA-IPv6RAO] |
+----------+-------------------------+------------------------------+
Note (*): The entry in the above table for the IPv6 RAO Value of 35
(Aggregated Reservation Nesting Level 32) has been marked due to an
inconsistency in the text of [RFC 3175], and is consequently reflected
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RFC 5350 IANA Considerations for Router Alert September 2008
in the IANA registry. In that document, the values 3-35 (i.e., 33
values) are defined for nesting levels 0-31 (i.e., 32 levels).
Similarly, value 3 is a duplicate, because aggregation level 0 means
end-to-end signaling, and this already has an IPv6 RAO value "1"
assigned.
Also note that nesting levels begin at 1 for IPv4 (described in
Section 1.4.9 of [RFC 3175]) and 0 for IPv6 (allocated in Section 6 of
[RFC 3175]).
Section 3.2 of this document redefines these so that for IPv6, value
3 is no longer used and values 4-35 represent levels 1-32. This
removes the above inconsistencies.
3. IANA Considerations
This section contains the new procedures for managing IPv4 Router
Alert Option Values. IANA has created a registry for IPv4 Router
Alert Option Values (described in Section 3.1) and has updated the
IPv6 Router Alert Option Values (described in Section 3.2).
IP Router Alert Option Values are currently managed separately for
IPv4 and IPv6. This document does not change this, as there is
little value in forcing the two registries to be aligned.
3.1. IANA Considerations for IPv4 Router Alert Option Values
The Value field, as specified in [RFC 2113], is two octets in length.
The Value field is registered and maintained by IANA. The initial
contents of this registry are:
+-------------+--------------------------------------+-----------+
| Value | Description | Reference |
+-------------+--------------------------------------+-----------+
| 0 | Router shall examine packet | [RFC 2113] |
| 1-32 | Aggregated Reservation Nesting Level | [RFC 3175] |
| 33-65502 | Available for assignment by the IANA | |
| 65503-65534 | Available for experimental use | |
| 65535 | Reserved | |
+-------------+--------------------------------------+-----------+
New values are to be assigned via IETF Review as defined in
[RFC 5226].
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RFC 5350 IANA Considerations for Router Alert September 2008
3.2. IANA Considerations for IPv6 Router Alert Option Values
The registry for IPv6 Router Alert Option Values continues to be
maintained as specified in [RFC 2711]. In addition, the following
value has been removed from the IANA registry and reserved for
possible future use (not to be allocated currently). The reason is
that it is a duplicate value; aggregation level 0 means end-to-end
signaling, and this already has an IPv6 RAO value "1" assigned.
+-------+--------------------------+-----------+
| Value | Description | Reference |
+-------+--------------------------+-----------+
| 3 | RSVP Aggregation level 0 | [RFC 3175] |
+-------+--------------------------+-----------+
The following IPv6 RAO values are available for experimental use:
+-------------+------------------+-----------+
| Value | Description | Reference |
+-------------+------------------+-----------+
| 65503-65534 | Experimental use | |
+-------------+------------------+-----------+
4. Security Considerations
Since this document is only concerned with the IANA management of the
IPv4 and IPv6 Router Alert Option Values registry, it raises no new
security issues beyond those identified in [RFC 2113] and [RFC 2711].
Yet, as discussed in RFC 4727 [RFC 4727], production networks do not
necessarily support the use of experimental code points in IP option
headers. The network scope of support for experimental values should
be evaluated carefully before deploying any experimental RAO value
across extended network domains, such as the public Internet. The
potential to disrupt the stable operation of the network hosting the
experiment through the use of unsupported experimental code points is
a serious consideration when planning an experiment using such code
points.
When experimental RAO values are deployed within an administratively
self-contained network domain, the network administrators should
ensure that each value is used consistently to avoid interference
between experiments. When experimental values are used in traffic
that crosses multiple administrative domains, the experimenters
should assume that there is a risk that the same values will be used
simultaneously by other experiments, and thus that there is a
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RFC 5350 IANA Considerations for Router Alert September 2008
possibility that the experiments will interfere. Particular
attention should be given to security threats that such interference
might create.
5. Acknowledgements
Thanks to Robert Hancock, Martin Stiemerling, Alan Ford, and Francois
Le Faucheur for their helpful comments on this document.
6. References
6.1. Normative References
[RFC 2113] Katz, D., "IP Router Alert Option", RFC 2113,
February 1997.
[RFC 2711] Partridge, C. and A. Jackson, "IPv6 Router Alert
Option", RFC 2711, October 1999.
[RFC 3175] Baker, F., Iturralde, C., Le Faucheur, F., and B.
Davie, "Aggregation of RSVP for IPv4 and IPv6
Reservations", RFC 3175, September 2001.
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP
26, RFC 5226, May 2008.
6.2. Informative References
[IANA-IPv6RAO] "IANA Registry for Internet Protocol version 6 (IPv6)
Router Alert Option Values", <http://www.iana.org>.
[RFC 2205] Braden, R., Ed., Zhang, L., Berson, S., Herzog, S.,
and S. Jamin, "Resource ReSerVation Protocol (RSVP)
-- Version 1 Functional Specification", RFC 2205,
September 1997.
[RFC 2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999.
[RFC 3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and
A. Thyagarajan, "Internet Group Management Protocol,
Version 3", RFC 3376, October 2002.
[RFC 4286] Haberman, B. and J. Martin, "Multicast Router
Discovery", RFC 4286, December 2005.
Manner & McDonald Standards Track PAGE 6
RFC 5350 IANA Considerations for Router Alert September 2008
[RFC 4727] Fenner, B., "Experimental Values In IPv4, IPv6,
ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727,
November 2006.
[Schwartz2000] Schwartz, B., Jackson, A., Strayer, W., Zhou, W.,
Rockwell, D., and C. Partridge, "Smart Packets:
Applying Active Networks to Network Management", ACM
Transactions on Computer Systems (TOCS), Volume 18,
Issue 1, February 2000.
Authors' Addresses
Jukka Manner
Department of Communications and Networking (Comnet)
Helsinki University of Technology (TKK)
P.O. Box 3000
Espoo FIN-02015 TKK
Finland
Phone: +358 9 451 2481
EMail: jukka.manner@tkk.fi
Andrew McDonald
Roke Manor Research Ltd (a Siemens company)
Old Salisbury Lane
Romsey, Hampshire SO51 0ZN
United Kingdom
EMail: andrew.mcdonald@roke.co.uk
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RFC 5350 IANA Considerations for Router Alert September 2008
Full Copyright Statement
Copyright © The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
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IANA Considerations for the IPv4 and IPv6 Router Alert Options
RFC TOTAL SIZE: 17812 bytes
PUBLICATION DATE: Thursday, September 11th, 2008
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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