Network Working Group J. Arkko
Request for Comments: 5494 Ericsson
Updates: 826, 951, 1044, 1329, 2131, C. Pignataro
2132, 2176, 2225, 2834, 2835, Cisco Systems
3315, 4338, 4361, 4701 April 2009
Category: Standards Track
IANA Allocation Guidelines for the Address Resolution Protocol (ARP)
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) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
This document specifies the IANA guidelines for allocating new values
in the Address Resolution Protocol (ARP). This document also
reserves some numbers for experimentation purposes. The changes also
affect other protocols that employ values from the ARP name spaces.
This document specifies the IANA guidelines [RFC5226] for allocating
new values for various fields in the Address Resolution Protocol
(ARP) [RFC0826]. The change is also applicable to extensions of ARP
that use the same message format, such as [RFC0903], [RFC1931], and
The change also affects other protocols that employ values from the
ARP name spaces. For instance, the ARP hardware address type
(ar$hrd) number space is also used in the "htype" (hardware address
type) fields in the Bootstrap Protocol (BOOTP) [RFC0951] and Dynamic
Host Configuration Protocol (DHCP) [RFC2131], as well as in the
"hardware type" field in the DHCP Unique Identifiers in DHCPv6
[RFC3315]. These protocols are therefore affected by the update in
the IANA rules. Other affected specifications include the
specialized address resolution mechanisms in:
o HYPERchannel [RFC1044]
o DHCP options [RFC2132] [RFC4361]
o ATM (Asynchronous Transfer Mode) ARP [RFC2225]
o HARP (High-Performance Parallel Interface ARP) [RFC2834] [RFC2835]
o Dual MAC (Media Access Control) FDDI (Fiber Distributed Data
Interface) ARP [RFC1329]
o MAPOS (Multiple Access Protocol over Synchronous Optical Network/
Synchronous Digital Hierarchy) ARP [RFC2176]
o FC (Fibre Channel) ARP [RFC4338]
o DNS DHCID Resource Record [RFC4701]
The IANA guidelines are given in Section 2. Previously, no IANA
guidance existed for such allocations. The purpose of this document
is to allow IANA to manage number assignments based on these
guidelines in a consistent manner.
This document also reserves some numbers for experimentation
purposes. These numbers are given in Section 3.
2. IANA Considerations
The following rules apply to the fields of ARP:
ar$hrd (16 bits) Hardware address space
Requests for ar$hrd values below 256 or for a batch of more than
one new value are made through Expert Review [RFC5226].
Note that certain protocols, such as BOOTP and DHCPv4, employ
these values within an 8-bit field. The expert should determine
that a need to allocate the new values exists and that the
existing values are insufficient to represent the new hardware
address types. The expert should also determine the applicability
of the request and assign values higher than 255 for requests that
do not apply to BOOTP/DHCPv4. Similarly, the expert should assign
1-octet values for requests that apply to BOOTP/DHCPv4, as for
example the "IPsec tunnel" with value 31 [RFC3456]. Conversely,
ARP-only uses, without a foreseeable reason to use the same value
in BOOTP/DHCPv4, should favor 2-octet values.
Requests for individual new ar$hrd values that do not specify a
value, or where the requested value is greater than 255, are made
through First Come First Served [RFC5226]. The assignment will
always result in a 2-octet value.
ar$pro (16 bits) Protocol address space
These numbers share the Ethertype space. The Ethertype space is
administered as described in [RFC5342].
ar$op (16 bits) Opcode
Requests for new ar$op values are made through IETF Review or IESG
3. Allocations Defined in This Document
When testing new protocol extension ideas, it is often necessary to
use an actual constant in order to use the new function, even when
testing in a closed environment. This document reserves the
following numbers for experimentation purposes in ARP:
o Two new ar$hrd values are allocated for experimental purposes:
HW_EXP1 (36) and HW_EXP2 (256). Note that these two new values
were purposely chosen so that one would be below 256 and the other
would be above 255, and so that there would be different values in
the least and most significant octets.
o Two new values for the ar$op are allocated for experimental
purposes: OP_EXP1 (24) and OP_EXP2 (25).
Note that Appendix B.2 of [RFC5342] lists two Ethertypes that can be
used for experimental purposes.
In addition, for both ar$hrd and ar$op, the values 0 and 65535 are
marked as reserved. This means that they are not available for
4. Security Considerations
This specification does not change the security properties of the
However, a few words are necessary about the use of the experimental
code points defined in Section 3. Potentially harmful side effects
from the use of the experimental values need to be carefully
evaluated before deploying any experiment across networks that the
owner of the experiment does not entirely control. Guidance given in
[RFC3692] about the use of experimental values needs to be followed.
The lack of any current rules has come up as new values were
requested from IANA, who contacted the IESG for advice. The author
would like to thank Michelle Cotton in particular for bringing up
this issue. The author would also like to thank Brian Carpenter,
Thomas Narten, Scott Bradner, Donald Eastlake, Andrew G. Malis, Brian
Haberman, Robert Sparks, Larry Zhu, and Dave Thaler for feedback.
6.1. Normative References
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC0951] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951,
[RFC1044] Hardwick, K. and J. Lekashman, "Internet Protocol on
Network System's HYPERchannel: Protocol specification",
STD 45, RFC 1044, February 1988.
[RFC1329] Kuehn, P., "Thoughts on Address Resolution for Dual MAC
FDDI Networks", RFC 1329, May 1992.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC2176] Murakami, K. and M. Maruyama, "IPv4 over MAPOS Version 1",
RFC 2176, June 1997.
[RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over
ATM", RFC 2225, April 1998.
[RFC2834] Pittet, J., "ARP and IP Broadcast over HIPPI-800",
RFC 2834, May 2000.
[RFC2835] Pittet, J., "IP and ARP over HIPPI-6400 (GSN)", RFC 2835,
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3692] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
[RFC4338] DeSanti, C., Carlson, C., and R. Nixon, "Transmission of
IPv6, IPv4, and Address Resolution Protocol (ARP) Packets
over Fibre Channel", RFC 4338, January 2006.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
[RFC4701] Stapp, M., Lemon, T., and A. Gustafsson, "A DNS Resource
Record (RR) for Encoding Dynamic Host Configuration
Protocol (DHCP) Information (DHCID RR)", RFC 4701,
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
[RFC5342] Eastlake. , D., "IANA Considerations and IETF Protocol
Usage for IEEE 802 Parameters", BCP 141, RFC 5342,
Appendix A. Changes from the Original RFCs
This document specifies only the IANA rules associated with various
fields in ARP. The specification of these rules also affects the
allocation of corresponding fields in protocols listed in Section 1
that share the registry. This document does not make any changes in
the operation of these protocols themselves.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709