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IANA rules Address Resolution Protocol ARP 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 for allocating new values for various fields in the Address Resolution Protocol (ARP) . The change is also applicable to extensions of ARP that use the same message format, such as , , 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 Bootstrap Protocol (BOOTP) and Dynamic Host Configuration Protocol (DHCP) , as well as in the "hardware type" field in the DHCP Unique Identifiers in DHCPv6 . These protocols are therefore affected by the update in the IANA rules. Other affected specifications include the specialized address resolution mechanisms in HYPERchannel , DHCP options , , ATM (Asynchronous Transfer Mode) ARP , HARP (High-Performance Parallel Interface ARP) , , Dual MAC FDDI (Fiber Distributed Data Interface) ARP , MAPOS (Multiple Access Protocol over Synchronous Optical Network/Synchronous Digital Hierarchy) ARP , FC (Fibre Channel) ARP , and DNS Resource Records . The IANA guidelines are given in . Previously, no IANA guidance existed for such allocations. This document also reserves some numbers for experimentation purposes. These numbers are given in .

The following rules apply to the fields of ARP: Requests for ar$hrd values below 256 or a batches of more than one new value are made through Expert Review . Note that certain protocols, such as BOOTP and DHCPv4 employ these values within a 8 bit field. The expert should determine that the need to allocate the new values exists and that the existing values are insufficient to represent the new hardware address types. The expert should also determine the applicability of the request, and assign values higher than 255 for requests that do not apply to BOOTP/DHCPv4. Similarly, the expert should assign one-octet values for requests that apply to BOOTP/DHCPv4, as for example the "IPsec tunnel" with value 31 . Conversely, ARP-only uses without a foreseeable reason to use the same value in BOOTP/DHCPv4 should favor 2-octet values. Requests for individual new ar$hrd values that do not specify a value, or where the requested value is greater than 255, are made through First Come First Served . The assignment will always result in a 2-octet value. These numbers share the Ethertype space. The Ethertype space is administered as described in . Requests for new ar$op values are made through IETF Review or IESG Approval .

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: Two new ar$hrd values are allocated for experimental purposes, HW_EXP1 (TBD-BY-IANA-1, but below 256) and HW_EXP2 (TBD-BY-IANA-2, but above 255 and preferably with different values in the least and most significant octets). Two new values for the ar$op are allocated for experimental purposes, OP_EXP1 (TBD-BY-IANA-3, any value will be sufficient) and OP_EXP2 (TBD-BY-IANA-4, any value will be sufficient). Note that , Section B.2 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 allocation.

This specification does not change the security properties of the affected protocols. However, a few words are necessary about the use of the experimental code points defined in . Potentially harmful side-effects from the use of the experimental values needs to be carefully evaluated before deploying any experiment across networks that the owner of the experiment does not entirely control. Guidance given in 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. The author would like to thank Michelle Cotton in particular for bringing this issue up. When no rules exist, IANA consults the IESG for approval of the new values. The purpose of this specification is to establish the rules and allow IANA to operate based on the rules, without requiring confirmation from the IESG. The author would also like to thank Brian Carpenter, Thomas Narten, Scott Bradner, Donald Eastlake, Andrew G. Malis, Brian Haberman, Robert Sparks, and Dave Thaler for feedback.

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 that share the registry. This document does not make any changes in the operation of these protocols themselves.