    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 (C) 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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    1.  Introduction

       The IP Router Alert Option is defined for IPv4 in [RFC2113].  A
       similar IPv6 option is defined in [RFC2711].  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) [RFC2205] and IGMP [RFC3376].

       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 [RFC2113], 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 [RFC3175], 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
       [RFC2711] and the aggregation-level allocations in [RFC3175] have

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       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 [RFC2113] and [RFC3175] 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 [RFC2113]        | Multicast Listener Discovery |
       |          | [RFC2205] [RFC3376]     | message [RFC2711] [RFC2710]  |
       |          | [RFC4286]               | [RFC4286]                    |
       | 1        | Aggregated Reservation  | Datagram contains RSVP       |
       |          | Nesting Level 1         | message [RFC2711] [RFC2205]  |
       |          | [RFC3175]               |                              |
       | 2        | Aggregated Reservation  | Datagram contains an Active  |
       |          | Nesting Level 2         | Networks message [RFC2711]   |
       |          | [RFC3175]               | [Schwartz2000]               |
       | 3        | Aggregated Reservation  | Aggregated Reservation       |
       |          | Nesting Level 3         | Nesting Level 0 [RFC3175](*) |
       |          | [RFC3175]               |                              |
       | 4        | Aggregated Reservation  | Aggregated Reservation       |
       |          | Nesting Level 4         | Nesting Level 1 [RFC3175]    |
       |          | [RFC3175]               |                              |
       | 5        | Aggregated Reservation  | Aggregated Reservation       |
       |          | Nesting Level 5         | Nesting Level 2 [RFC3175]    |
       |          | [RFC3175]               |                              |
       | ...      | ...                     | ...                          |
       | 32       | Aggregated Reservation  | Aggregated Reservation       |
       |          | Nesting Level 32        | Nesting Level 29 [RFC3175]   |
       |          | [RFC3175]               |                              |
       | 33       | Reserved                | Aggregated Reservation       |
       |          |                         | Nesting Level 30 [RFC3175]   |
       | 34       | Reserved                | Aggregated Reservation       |
       |          |                         | Nesting Level 31 [RFC3175]   |
       | 35       | Reserved                | Aggregated Reservation       |
       |          |                         | Nesting Level 32(*)          |
       |          |                         | [RFC3175]                    |
       | 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 [RFC3175], and is consequently reflected

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       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 [RFC3175]) and 0 for IPv6 (allocated in Section 6 of
       [RFC3175]).

       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 [RFC2113], 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          | [RFC2113] |
       | 1-32        | Aggregated Reservation Nesting Level | [RFC3175] |
       | 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
       [RFC5226].

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    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 [RFC2711].  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 | [RFC3175] |
       +-------+--------------------------+-----------+

       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 [RFC2113] and [RFC2711].

       Yet, as discussed in RFC 4727 [RFC4727], 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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       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

       [RFC2113]        Katz, D., "IP Router Alert Option", RFC 2113,
                        February 1997.

       [RFC2711]        Partridge, C. and A. Jackson, "IPv6 Router Alert
                        Option", RFC 2711, October 1999.

       [RFC3175]        Baker, F., Iturralde, C., Le Faucheur, F., and B.
                        Davie, "Aggregation of RSVP for IPv4 and IPv6
                        Reservations", RFC 3175, September 2001.

       [RFC5226]        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>.

       [RFC2205]        Braden, R., Ed., Zhang, L., Berson, S., Herzog, S.,
                        and S. Jamin, "Resource ReSerVation Protocol (RSVP)
                        -- Version 1 Functional Specification", RFC 2205,
                        September 1997.

       [RFC2710]        Deering, S., Fenner, W., and B. Haberman, "Multicast
                        Listener Discovery (MLD) for IPv6", RFC 2710,
                        October 1999.

       [RFC3376]        Cain, B., Deering, S., Kouvelas, I., Fenner, B., and
                        A. Thyagarajan, "Internet Group Management Protocol,
                        Version 3", RFC 3376, October 2002.

       [RFC4286]        Haberman, B. and J. Martin, "Multicast Router
                        Discovery", RFC 4286, December 2005.

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       [RFC4727]        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

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