Internet Engineering Task Force                              S.D. Schoen
Internet-Draft                                                J. Gilmore
Updates: 1122, 1812, 3021 (if approved)                          D. Täht
Intended status: Standards Track         IPv4 Unicast Extensions Project
Expires: 21 March 2022                                         M. Karels
                                                       17 September 2021


                  The Lowest Address in an IPv4 Subnet
                 draft-schoen-intarea-lowest-address-01

Abstract

   With ever-increasing pressure to conserve IP address space on the
   Internet, it makes sense to consider where relatively minor changes
   can be made to fielded practice to improve numbering efficiency.  One
   such change, proposed by this document, is to increase the number of
   unicast addresses in each existing subnet, by redefining the use of
   the lowest-numbered (zeroth) host address in each IPv4 subnet as an
   ordinary unicast host identifier, instead of as a duplicate segment-
   directed broadcast address.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 March 2022.

Copyright Notice

   Copyright (c) 2021 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 (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights



Schoen, et al.            Expires 21 March 2022                 [Page 1]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   and restrictions with respect to this document.  Code Components
   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Background and Current Standards  . . . . . . . . . . . . . .   3
     2.1.  Assumptions About the Lowest Host Address by Remote
           Systems . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Multicast Addresses; Point-to-Point Links . . . . . . . .   6
     2.3.  Current Limitations on Subnet-Directed Broadcast
           Addresses . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Comparison to IPv6 Behavior . . . . . . . . . . . . . . .   6
   3.  Change to Interpretation of the Lowest Address  . . . . . . .   7
     3.1.  Link-Layer Interaction  . . . . . . . . . . . . . . . . .   7
     3.2.  Recommendations . . . . . . . . . . . . . . . . . . . . .   8
       3.2.1.  "Requirements for Internet Hosts -- Communication
               Layers" [RFC1122] . . . . . . . . . . . . . . . . . .   8
       3.2.2.  "Requirements for IP Version 4 Routers" [RFC1812] . .   8
     3.3.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  10
     3.4.  Compatibility and Interoperability  . . . . . . . . . . .  11
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   This document provides history and rationale to change the
   interpretation of the lowest address in each IPv4 subnet from an
   alternative broadcast address to an ordinary assignable host address,
   and updates requirements for hosts and routers accordingly.  The
   decision taken in 1989 to reserve two forms instead of one for local
   IPv4 segment broadcasts is no longer necessary because of the
   obsolescence and disappearance of the software that motivated it.
   Unreserving the lowest address provides an optional extra IPv4 host
   address in every subnet, Internet-wide, alleviating some of the
   pressure of IPv4 address exhaustion.







Schoen, et al.            Expires 21 March 2022                 [Page 2]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Background and Current Standards

   IPv4 has long supported several mechanisms for broadcasting
   communications to every station on a network.  One form of broadcast
   in IPv4 is "segment-directed broadcast" in which a broadcast is
   addressed to every station on a particular network (identified by its
   network number).  Current standards reserve a huge number of
   addresses for this: not just one, but two, addresses per subnet,
   Internet-wide.

   The standard broadcast address on a subnet is the address whose "host
   part" consists of all ones in binary.  For example, in a 24-bit
   subnet that starts at 192.168.3.0, the address 192.168.3.255 is the
   standard broadcast address.  [RFC1122][RFC0894]

   In addition to the standard broadcast address, RFC 1122 (October
   1989) acknowledged a then-current implementation behavior in "4.2BSD
   Unix and its derivatives, but not 4.3BSD", whereby those operating
   systems "use non-standard broadcast address forms, substituting 0 for
   -1".  (Note that there was no standard for IP broadcast when 4.2BSD
   was released in August 1983, more than a year prior to [RFC0919].
   The -1 form was first proposed in [IEN212] in 1982 but was not yet a
   standard.)  According to RFC 1122 and its successors, Internet hosts
   are expected to "recognize and accept [...] these non-standard
   broadcast addresses as the destination address of an incoming
   datagram", and not otherwise use them to identify Internet hosts.
   RFCs 1812 [RFC1812] (sections 4.2.3.1 and 5.3.5), and 3021 [RFC3021]
   (sections 2.2, 3.1, and 3.3) reiterate and further expand on this
   requirement.

   This non-standard broadcast address is the address whose "host part"
   consists of all zeroes.  (The quantity of zeroes depends, in present-
   day terminology, on the applicable subnet mask.)  This address is the
   lowest expressible address within any particular numbered network.
   Following computer science tradition, it may also be referred to as
   the "zeroth address" of its respective subnet.

   The address triple syntax used in RFC 1122 looks unusual to modern
   eyes.  These triples included the "{ network number, subnet number,
   host number }".  The notation also used two's complement binary
   notation in referring to a host number "-1" as containing all binary
   1-bits.  After the widespread adoption of CIDR [RFC4632], network



Schoen, et al.            Expires 21 March 2022                 [Page 3]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   numbers no longer have an "address class" definition based on their
   high-order bits, and there is no distinction between a network number
   and a subnet number (except locally at the router where individual
   subnets are being routed).  Instead, following RFC 4632, IPv4 network
   addresses are denoted with a dotted-decimal format containing one to
   four positive 8-bit integers, a slash, and a whole count of the bits
   in the network number portion, the so-called CIDR notation,
   reportedly devised by Phil Karn.  So for example 192.1.2.0/28 has a
   28-bit network number and a 4-bit host number (32 address bits total,
   minus those 28 bits).  All of the bits of that particular host number
   are zero (because the whole fourth dotted number is 0), and thus the
   interpretation of this address would be affected by this document.
   We will use both notations as convenient.  Where RFC 1122 and its
   successors use the terms "0 form" and "-1 form", we may refer
   respectively to "all-zeros" and "all-ones" host numbers, since every
   bit in the binary representation of these two host numbers has the
   value 0 or 1, respectively.

   4.2BSD, the operating system to whose behavior RFC 1122 required
   deference, was the first BSD operating system full release to include
   TCP/IP support; it was released in 1983.  Its successor, 4.3BSD, was
   released in 1986, which is why RFC 1122 could already confirm that
   the broadcast behavior had been changed.  See [BSDHIST].  RFC 1812
   calls the old behavior "obsolete" in 1995, and RFC 3021 reiterates
   that it is "obsolete" in 2000, although both express the idea that
   the lowest address must continue to be reserved for historical
   reasons.

   All subsequent operating systems used on the Internet implement the
   standard all-ones form of the broadcast address and use it by
   default.  Continuing to reserve the non-standard all-zeroes form
   wastes one IPv4 address per subnet.  No known operating system
   generates IP broadcasts in this format today, and documentation
   consistently encourages network administrators and software
   developers to use the standard form.  The IPv4 protocol does not
   benefit from having two different broadcast addresses with the same
   functionality in every subnet, and the non-standard form has always
   been reserved primarily for backwards compatibility with systems that
   have not existed for decades on the Internet.

   As IPv4 addresses were not perceived as particularly scarce through
   the 1980s, the prospect of wasting tens of millions of otherwise
   assignable addresses in order to achieve backwards compatibility with
   a particular operating system appeared reasonable.  Today, those
   addresses are clearly valuable and could be put to good use as
   identifiers of Internet hosts in a time of IPv4 numbering resource
   exhaustion.




Schoen, et al.            Expires 21 March 2022                 [Page 4]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


2.1.  Assumptions About the Lowest Host Address by Remote Systems

   In general, under CIDR [RFC4632], only hosts and routers on a network
   segment know that segment's netmask with certainty.  Remote parts of
   the Internet are already expected to not make assumptions about
   whether or not a particular address is a broadcast address, since
   that determination is already only meaningful for devices connected
   to the segment containing that address.  This document does not
   change any of these things.  Thus, if the behavior of devices on a
   particular network segment has been updated in accordance with this
   memo, the lowest address on that segment can already be addressed by
   hosts elsewhere on the Internet without any changes to their own
   software.

   [RFC1812] noted in section 4.2.3.1 that whether a reserved address is
   treated specially at all depends on one's vantage point on the
   network:

   |  [a] router obviously cannot recognize addresses of the form {
   |  <Network-prefix>, 0 } if the router has no interface to that
   |  network prefix.  In that case, the rules of the second bullet
   |  [requiring a packet to be discarded] do not apply because, from
   |  the point of view of the router, the packet is not an IP broadcast
   |  packet.

   It also noted in section 5.3.5.2 that

   |  in view of CIDR, such [packets addressed to broadcast addresses of
   |  distant networks] appear to be host addresses within the network
   |  prefix; we preclude inspection of the host part of such network
   |  prefixes.

   To the extent that software continues to make assumptions about IP
   network classes today, it is out of compliance with RFC 4632.  Ever
   since the adoption of CIDR in RFC 1519, it has been unknowable
   whether or to what extent the remote network would internally
   aggregate or deaggregate routes that were visible elsewhere on the
   Internet.  Therefore, Internet hosts and routers MUST NOT assume that
   an IPv4 address on a remote network, other than 0.0.0.0, is invalid,
   unroutable, or unaddressable merely because it ends with a particular
   number of zeroes.  In keeping with the Internet's end-to-end
   principle, decisions about possible invalidity of otherwise routable
   addresses belong as close to the endpoints as possible.








Schoen, et al.            Expires 21 March 2022                 [Page 5]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


2.2.  Multicast Addresses; Point-to-Point Links

   Multicast addresses, as defined by RFC 1112 [RFC1112], do not have a
   network part and host part, nor do they have a netmask or CIDR prefix
   length.  IPv4 multicast addresses, except 224.0.0.0 (which is
   "guaranteed not to be assigned to any group" by RFC 1112), could
   always end with any number of zeroes, and have never had any form of
   directed broadcast address.

   [RFC3021], section 2.1, standardized that, in a point-to-point link
   using a 31-bit netmask, the all-zero and all-one forms of the host-
   part of the address MUST both be treated as unicast ("host")
   addresses.

   The present document does not change the interpretation of multicast
   addresses or 31-bit subnet addresses in any way.

2.3.  Current Limitations on Subnet-Directed Broadcast Addresses

   Sending packets to a subnet-directed broadcast address is still
   generally useful in today's Internet, but only for nodes attached
   directly to that subnet.  [RFC2644] discouraged routers from
   forwarding such packets, to reduce their use in amplifying denial-of-
   service attacks, so they often cannot be received when sent from
   distant hosts.  Many hosts today ignore ICMP packets sent as
   broadcasts, so a directed broadcast ping is no longer a reliable
   means of enumerating all hosts attached to a network.  As
   Informational [RFC6250] notes, "broadcast can only be relied on
   within a link".

2.4.  Comparison to IPv6 Behavior

   In IPv6 there are no reserved per-segment broadcast addresses (or,
   indeed, any broadcast addresses whatsoever).  Instead, IPv6 hosts can
   address all hosts on a network segment by using the link-local
   multicast group address ff02::1 [RFC4291], which, for example,
   produces a multicast Ethernet frame when transmitted over an
   Ethernet-like link [RFC2464].  The lowest address on a subnet is,
   however, reserved in IPv6 by Section 2.6.1 of RFC 4291 [RFC4291] for
   the Subnet-Router address (a means of addressing "any router" on an
   indicated subnet).










Schoen, et al.            Expires 21 March 2022                 [Page 6]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


3.  Change to Interpretation of the Lowest Address

   The purpose of this document is to designate the all-zeros address in
   each subnet as a unicast address.  All such addresses are now
   available for general non-broadcast use, treated identically to all
   host addresses in the subnet besides the "all-ones" broadcast
   address.  This document therefore eliminates an element of the IPv4
   protocol's historical adaptation to 4.2BSD's behavior.  All hosts
   SHOULD continue to recognize and accept only the all-ones form of the
   IPv4 subnet broadcast address.

   Host software that intends to transmit a segment-directed broadcast
   packet in an IPv4 network MUST use only the all-ones form as the
   destination address of the packet.

   An IPv4 datagram containing a source or destination that is equal to
   the all-zeroes form of the local broadcast address SHOULD be treated,
   by both hosts and routers, as a normal unicast datagram; it SHOULD
   NOT be treated as a local broadcast datagram.

   Host software SHOULD allow a network interface to be configured with
   the lowest address on a subnet.  A host with such an address
   configured MUST use this assigned address as a source address for
   datagrams just as it would with any other assigned interface address,
   and MUST recognize a datagram sent to that address as addressed to
   itself.  Host software SHOULD be capable of generating unicast
   packets to the lowest address on a subnet when so requested by an
   application, and MUST encapsulate such packets into link-layer
   unicast frames when transmitted on a link layer that distinguishes
   unicast and broadcast.

   Clients for autoconfiguration mechanisms such as DHCP [RFC2131]
   SHOULD accept a lease or assignment of the lowest address whenever
   the underlying operating system is capable of accepting it.  Servers
   for these mechanisms SHOULD assign this address when so configured.
   The network operator of each subnet retains the discretion to number
   hosts on that subnet with, or without, the use of the lowest address,
   based on local conditions.

3.1.  Link-Layer Interaction

   The link layer always indicates to the IP layer whether or not a
   datagram was transmitted as a broadcast at the link layer.  Hosts
   MUST continue to follow the RFC 1122 rule about link-layer broadcast
   indications:






Schoen, et al.            Expires 21 March 2022                 [Page 7]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   |  A host SHOULD silently discard a datagram that is received via a
   |  link-layer broadcast [...] but does not specify an IP multicast or
   |  broadcast destination address.

   This rule is, among other things, intended to avoid broadcast storms.
   This document now defines the lowest address as a non-broadcast
   address.  Therefore, a host SHOULD silently discard a datagram
   received via a link-layer broadcast whose destination address is the
   lowest IPv4 address in a subnet.  This is true even if the interface
   on which the host received that datagram uses the lowest address as a
   unicast IPv4 address.

3.2.  Recommendations

   The considerations presented in this document affect other published
   work.  This section details the updates made to other documents.

3.2.1.  "Requirements for Internet Hosts -- Communication Layers"
        [RFC1122]

   The new section numbered 3.2.1.3 (h) which was added by RFC 3021 is
   replaced with:

   |  (h) { <Network-number>, <Subnet-number>, 0 }
   |
   |  An ordinary unicast ("host") address in the subnet.  May be used
   |  as either a source or destination address.  If a link-level
   |  broadcast packet is received with this address (or any other
   |  unicast address) as its destination, it MUST be silently
   |  discarded.  Such a packet may be sent by long-obsolete hosts on
   |  the local network.
   |
   |  In applications using CIDR notation [RFC4632], this address, or
   |  any other address in the subnet, may also be used together with a
   |  prefix length to refer to the entire subnet.

3.2.2.  "Requirements for IP Version 4 Routers" [RFC1812]

   The new section (numbered 4.2.2.11 (f)) added by RFC 3021 is replaced
   by:

   |  (f) { <Network-prefix>, 0 }
   |








Schoen, et al.            Expires 21 March 2022                 [Page 8]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   |  An ordinary unicast ("host") address in the subnet.  May be used
   |  as either a source or destination address.  If a link-layer
   |  broadcast packet is received with this address (or any other
   |  unicast address) as its destination, it MUST be silently
   |  discarded.  Such a packet may be sent by long-obsolete hosts on
   |  the local network.
   |
   |  In applications using CIDR notation [RFC4632], this address, or
   |  any other address in the subnet, may also be used together with a
   |  prefix length to refer to the entire subnet.

   The first paragraph on page 49 (which appears after section 4.2.2.11
   (e) in the original RFC 1812, or after section 4.2.2.11 (f) in RFC
   1812 as modified by RFC 3021) is changed from this original text

   |  IP addresses are not permitted to have the value 0 or -1 for the
   |  <Host-number> or <Network-prefix> fields except in the special
   |  cases listed above.  This implies that each of these fields will
   |  be at least two bits long.
   |
   |  DISCUSSION
   |
   |  Previous versions of this document also noted that subnet numbers
   |  must be neither 0 nor -1, and must be at least two bits in length.
   |  In a CIDR world, the subnet number is clearly an extension of the
   |  network prefix and cannot be interpreted without the remainder of
   |  the prefix.  This restriction of subnet numbers is therefore
   |  meaningless in view of CIDR and may be safely ignored.

   to this new text

   |  Unicast IP addresses are permitted to have the value 0 for the
   |  <Host-number> field, and may have the value -1 in the special
   |  cases listed above.  There is no requirement that the <Host-
   |  number> field be any particular length.  In some cases using CIDR
   |  notation, a host may be designated with a /32 suffix (e.g.
   |  192.0.2.34/32), indicating that the specific host rather than its
   |  subnet is being described.
   |
   |  DISCUSSION
   |
   |  Previous versions of this document also noted that subnet numbers
   |  must be neither 0 nor -1, and must be at least two bits in length.
   |  Other versions required that <Network-prefix> fields must be
   |  neither 0 nor -1, and must be at least two bits long.
   |





Schoen, et al.            Expires 21 March 2022                 [Page 9]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   |  Now that the Internet has fully transitioned to CIDR routing,
   |  there are no original classful <Network-number>s to be
   |  distinguished from <Subnet-numbers>.  Each address only has a
   |  <Network-prefix> based on its network mask (or equivalently, the
   |  CIDR suffix specifying how many bits are in the <Network-prefix>).
   |  The former restrictions on subnet numbers and their sizes are
   |  meaningless in view of CIDR and are hereby repealed.  For example,
   |  a route to 0.0.0.0/6 or even 0.0.0.0/1 is a viable CIDR route (for
   |  the aggregation of the blocks 0/8, 1/8, 2/8, and 3/8; or for the
   |  entire lower half of the IPv4 address space) and should not be
   |  considered invalid. 0.0.0.0/0 is standardized to mean "all unicast
   |  IPv4 addresses", e.g. in a default route, by section 5.1 of
   |  [RFC4632], which MUST also continue to work.

   Sections 4.2.3.1 (2) and (4) are replaced with:

   |  (2) SHOULD silently discard on receipt (i.e., do not even deliver
   |  to applications in the router) any packet addressed to 0.0.0.0.
   |  If these packets are not silently discarded, they MUST be treated
   |  as IP broadcasts (see Section [5.3.5]).  There MAY be a
   |  configuration option to allow receipt of these packets.  This
   |  option SHOULD default to discarding them.
   |
   |  A packet addressed to { <Network-prefix>, 0 } is an ordinary
   |  unicast packet, and MUST be treated as such.
   |
   |  (4) SHOULD NOT originate datagrams addressed to 0.0.0.0.  SHOULD
   |  allow for the generation of datagrams addressed to {<Network-
   |  prefix>, 0 } since that is now defined as an ordinary unicast
   |  adddress.

3.3.  Example

   The only IPv4 broadcast address for 192.168.42.0/24 is 192.168.42.255
   (the all-ones or "-1" host number). 192.168.42.0 (the all-zeroes or
   "0" host number) was formerly a second broadcast address on that
   subnet, but is now a unicast address.

   The fact that the address identifier 192.168.42.0 can refer to both a
   network and a specific host 192.168.42.0 is not unusual.  Similarly,
   referring to a subnet as 192.168.42.0/24 and configuring a particular
   interface on that subnet as 192.168.42.0/24 is also not unusual.
   Computer scientists normally count all sorts of things starting at
   the zeroth (lowest) element in a sequence.[EWD831] For example, the
   initial element in an array is likely to be stored at a memory
   address equal to the memory address of the array itself.[ARRAY]
   Similarly, IPv4 hosts in a subnet MAY be enumerated starting with an
   address that matches the address of the subnet itself.



Schoen, et al.            Expires 21 March 2022                [Page 10]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   Similarly, the only IPv4 broadcast address for the subnet
   192.168.42.96/28 is 192.168.42.111.  The address 192.168.42.96 MAY be
   assigned to an individual host on this network.

3.4.  Compatibility and Interoperability

   Many deployed systems follow older Internet standards in not allowing
   the lowest address in a network to be assigned or used as a source or
   destination address.  Assigning this address to a host may thus make
   it unaddressable by some devices on its local network segment.
   Network operators considering assigning this address to a host should
   investigate their own network environments to determine whether their
   interoperability requirements will be met.  Interoperability with
   these addresses is likely to improve over time, following the
   publication of this document.

   Prior standards required hosts and gateways to ignore, and to refrain
   from generating, non-broadcast datagrams from or to the lowest
   address.  So when a single network contains a device that has been
   assigned the lowest address as specified by this document, along with
   one or more devices that follow the traditional behavior, the
   traditional devices will not be able to communicate with the lowest-
   address device at all.  Other sorts of malfunctions are unlikely,
   because the former standards (RFC 1122) required traditional hosts to
   drop any unicast packet addressed to the secondary broadcast address
   that they implemented at the lowest address.

4.  IANA Considerations

   This memo includes no request to IANA.

5.  Security Considerations

   The behavior change specified by this document could produce security
   concerns where two devices, or two different pieces of software on a
   single host, or a software application and a human user, follow
   divergent interpretations of the lowest address on a network.  For
   example, this could lead to errors in the specification or
   enforcement of rules about Internet hosts' connectivity to one
   another, or their right to access resources.

   Firewall rules that assume that the lowest address on a subnet cannot
   be addressed SHOULD be updated to take into account that it can be
   addressed, so as to avoid either unintentionally allowing or
   unintentionally forbidding connections involving it.  Other security,
   monitoring, or logging systems that treat the lowest address as an
   unaddressable bogon address SHOULD likewise be updated.




Schoen, et al.            Expires 21 March 2022                [Page 11]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   Host software SHOULD make the distinction between lowest-address
   (considered individually) and subnet (considered as a group) clear to
   users, where this distinction is relevant and could be a subject of
   confusion.

6.  Acknowledgements

   This document directly builds on prior work by Dave T&#228;ht and
   John Gilmore as part of the IPv4 Unicast Extensions Project.

7.  References

7.1.  Normative References

   [RFC0919]  Mogul, J., "Broadcasting Internet Datagrams", STD 5,
              RFC 919, DOI 10.17487/RFC0919, October 1984,
              <https://www.rfc-editor.org/info/rfc919>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <https://www.rfc-editor.org/info/rfc1122>.

   [RFC1812]  Baker, F., Ed., "Requirements for IP Version 4 Routers",
              RFC 1812, DOI 10.17487/RFC1812, June 1995,
              <https://www.rfc-editor.org/info/rfc1812>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
              (CIDR): The Internet Address Assignment and Aggregation
              Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
              2006, <https://www.rfc-editor.org/info/rfc4632>.

7.2.  Informative References

   [ARRAY]    Wikipedia, "C Programming Language: Array-pointer
              interchangeability", <https://en.wikipedia.org/wiki/C_(pro
              gramming_language)#Array%E2%80%93pointer_interchangeabilit
              y>.

   [BSDHIST]  Wikipedia, "History of the Berkeley Software
              Distribution", <https://en.wikipedia.org/wiki/
              History_of_the_Berkeley_Software_Distribution>.




Schoen, et al.            Expires 21 March 2022                [Page 12]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   [EWD831]   Dijkstra, E.W., "Why Numbering Should Start at Zero",
              August 1982,
              <https://www.cs.utexas.edu/users/EWD/transcriptions/
              EWD08xx/EWD831.html>.

   [IEN212]   Gurwitz, R. and R. Hinden, "IP - Local Area Network
              Addressing Issues", IEN 212, September 1982,
              <https://www.postel.org/ien/pdf/ien212.pdf>.

   [RFC0894]  Hornig, C., "A Standard for the Transmission of IP
              Datagrams over Ethernet Networks", STD 41, RFC 894,
              DOI 10.17487/RFC0894, April 1984,
              <https://www.rfc-editor.org/info/rfc894>.

   [RFC1112]  Deering, S., "Host extensions for IP multicasting", STD 5,
              RFC 1112, DOI 10.17487/RFC1112, August 1989,
              <https://www.rfc-editor.org/info/rfc1112>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
              Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
              <https://www.rfc-editor.org/info/rfc2464>.

   [RFC2644]  Senie, D., "Changing the Default for Directed Broadcasts
              in Routers", BCP 34, RFC 2644, DOI 10.17487/RFC2644,
              August 1999, <https://www.rfc-editor.org/info/rfc2644>.

   [RFC3021]  Retana, A., White, R., Fuller, V., and D. McPherson,
              "Using 31-Bit Prefixes on IPv4 Point-to-Point Links",
              RFC 3021, DOI 10.17487/RFC3021, December 2000,
              <https://www.rfc-editor.org/info/rfc3021>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC6250]  Thaler, D., "Evolution of the IP Model", RFC 6250,
              DOI 10.17487/RFC6250, May 2011,
              <https://www.rfc-editor.org/info/rfc6250>.

Authors' Addresses







Schoen, et al.            Expires 21 March 2022                [Page 13]


Internet-Draft    The Lowest Address in an IPv4 Subnet    September 2021


   Seth David Schoen
   IPv4 Unicast Extensions Project
   San Francisco, CA
   United States of America

   Email: schoen@loyalty.org


   John Gilmore
   IPv4 Unicast Extensions Project
   PO Box 170640-rfc
   San Francisco, CA 94117-0640
   United States of America

   Email: gnu@rfc.toad.com


   David M. Täht
   IPv4 Unicast Extensions Project
   Half Moon Bay, CA
   United States of America

   Email: dave@taht.net


   Michael J. Karels
   Eden Prairie, MN
   United States of America

   Email: rfc@karels.net





















Schoen, et al.            Expires 21 March 2022                [Page 14]