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 (C) The IETF Trust (2008).
This document updates the IANA allocation rules and registry of IPv4
and IPv6 Router Alert Option Values.
Table of Contents
1. Introduction ....................................................22. Use of the Router Alert Option Value Field ......................23. IANA Considerations .............................................43.1. IANA Considerations for IPv4 Router Alert Option Values ....43.2. IANA Considerations for IPv6 Router Alert Option Values ....54. Security Considerations .........................................55. Acknowledgements ................................................66. References ......................................................66.1. Normative References .......................................66.2. Informative References .....................................6
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
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
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
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"
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
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
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
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
possibility that the experiments will interfere. Particular
attention should be given to security threats that such interference
Thanks to Robert Hancock, Martin Stiemerling, Alan Ford, and Francois
Le Faucheur for their helpful comments on this document.
6.1. Normative References
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
[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,
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
[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.
[RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6,
ICMPv4, ICMPv6, UDP, and TCP Headers", RFC 4727,
[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.
Department of Communications and Networking (Comnet)
Helsinki University of Technology (TKK)
P.O. Box 3000
Espoo FIN-02015 TKK
Phone: +358 9 451 2481
Roke Manor Research Ltd (a Siemens company)
Old Salisbury Lane
Romsey, Hampshire SO51 0ZN
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