Network Working Group                                       B. Carpenter
Internet Draft                                                      CERN
                                                           21 March 1994
Expires 26 September 1994

File name draft-carpenter-aeiou-00.txt

              Address Extension by IP Option Usage (AEIOU)

Status of this Memo

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   This document proposes an addressing extension mechanism for IP as a
   possible life extender while awaiting IPng.

AEIOU proposal

   It is possible that no IPng candidate will be considered mature
   enough in time to be widely deployed before the IPv4 address space is
   fully allocated. This document suggests a way to cope with this risk.
   Although it does not propose a new IPng candidate, the proposal does
   amount to a major change to IP, requiring new versions of host and
   router software.  However, the impact on existing code is much less
   than that of any IPng proposal. By the same token, the only problem
   that it tackles is the address space problem.

   During the process of collecting requirements for IPng, a number of
   people have stated the need to fix the IPv4 address space problem by

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Draft         Address Extension by IP Option Usage (AEIOU) 21 March 1994

   flexible address extensions beyond 32 bits. However, if this means
   that IPv4 addresses should be replaced by bigger addresses, it breaks
   the current Internet routing and addressing architecture.

   AEIOU proposes to tackle the problem differently.  Firstly, three
   conservative measures should be taken:

   1. Do not extend the global Internet address space or modify the
   global routing architecture.

   2. Do deploy CIDR and BGP4. Be very restrictive on allocations to new
   sites (i.e. give them the minimum CIDR space that will satisfy them
   for one or two years).

   3. Do not allocate any new network numbers to sites that already have
   at least one network number of any class (A, B, C). Try to recover
   unused numbers and CIDRise sparse networks. Encourage use of RFC

   Secondly, provide a simple address extension mechanism as an IP

   4. Add two new IPv4 options "Source Address Extension" (SAE) and
   "Destination Address Extension" (DAE).

       Type:   [copied, class 0, option number TBD]
       Length: 6
       Data:   4 octet address extension (AE)

   The AE options are carried transparently and survive fragmentation.
   Neither, either, or both may be present.

   5. AEs are allocated by a site (not to a site) when it has run out of
   addresses in its share of the IPv4 32-bit address space. The AE space
   is structured like Class A, B and C space and all normal subnetting
   techniques apply. A host in AE space can be considered to have an
   address in the form of a 64-bit couplet (site address, AE).

   Each site has a globally unique 32-bit site address, which can be any
   IPv4 address from the site's IANA-allocated IPv4 address space. This
   site address then "hides" all the site's AEs. For example, the site
   currently allocated the Class B network 128.141 could use as its site address, and this would be the wide-area
   address used for routing all packets to the site's 32-bit AE space.
   Wide-area routing does not change.  Routing to non-AE hosts does not

   6. Hosts now fall into three classes:

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Draft         Address Extension by IP Option Usage (AEIOU) 21 March 1994

      OLD hosts; still running 32-bit IP only.
      NEW hosts; AE options implemented, but no allocated AE (i.e.
                 NEW hosts are still in the global 32-bit space.)
                 By convention, AE= for NEW hosts.
      AE  hosts; AE options implemented, and an AE allocated.
                 AE hosts are in the new 64-bit space.

   The following table shows which combinations of hosts can talk to
   each other, using 32 or 64 bit addresses.

              OLD    NEW     AE
        OLD | 32   | 32   |  no  |      (There might be some cases
            |      |      |      |       where OLD and AE hosts can
        NEW | 32   | 32   |  64  |       talk, if they are on the
            |      |      |      |       same subnet.)
        AE  | no   | 64   |  64  |

   The outline of the deployment plan follows.

   Stage 1: A site address is allocated for every Internet site.
            On-site routers are upgraded to AE.
            All servers are upgraded from OLD to NEW.
            OLD clients can still access NEW servers.

   Stage 2: Ensure that all newly installed clients are AE hosts.
            New clients no longer consume 32-bit addresses.

   Stage 3: Progressively convert OLD clients to AE. This means
            upgrading software versions, and renumbering clients.
            At the same time, RFC 1597 addresses could be transformed
            into AEs if required.

   Stage 4: Sites will now have many unused 32-bit addresses recovered
            during Stage 3. A fraction of these can be recovered by
            further use of CIDR, and can be re-allocated as site addresses
            for new Internet sites.

   Stage 5: Theoretically, all servers can now be converted from NEW to AE.
            At this stage almost all 32-bit addresses can be recovered
            and re-used as in Stage 4. We now have a two-tier Internet
            address scheme (32-bit site address space managed by IANA,
            and 32-bit AE space managed by individual sites).

   Thirdly, some more details:

   7. IP packets flow from source to the destination site exactly as

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Draft         Address Extension by IP Option Usage (AEIOU) 21 March 1994

   they do today. The SAE and DAE options are copied (even if
   fragmentation occurs).  At the ingress router on the destination
   site, if the DAE option is present, it is used by local routing
   protocols to route the packet to the correct physical subnet. These
   routing protocols can be any of those in use today, except that they
   look at the DAE field instead of the normal IP destination address

   This is not optimal for router performance. However, the obvious
   solution of having the ingress router swap the DAE and the DA does
   not work, since this would disturb the TCP and UDP pseudo-header
   checksum calculation.

   8. On a subnet such as Ethernet, a rather straightforward extension
   of ARP (EARP, extended ARP) is needed to obtain the physical address
   corresponding to the (site address,DAE) couplet. For further study,
   but clearly soluble.

   9. DNS RR's will include the AE when it exists. The DNS reply will
   directly imply whether a host is OLD (no AE), NEW (AE = or

   10. I haven't worked out how the AE is handled at the socket API yet.
   This is the biggest problem if software changes are to be minimised.
   It's no worse than for SIPP, of course. It can also be argued that
   forcing applications to use an API with multiple address formats (for
   example, AF_INET and AF_INETE in the case of BSD sockets) is good,
   because this will be needed for the real IPng when it comes.

   11. FOOBAR (RFC 1545) can handle it for FTP.

   12. etc. Lots more to be written, by analogy with the SIPP and TUBA
   transition documents.



Disclaimer and acknowledgements.

   This is a personal view and does not necessarily represent that of my

   AEIOU is not the same as EIP (RFC 1385) but it is in some sense a
   simple inversion of the EIP idea, which has been at the back of my
   mind for two years. It resembles the original (1992) IPAE draft too
   and has some similarities to TP/IX (RFC 1475). Other ideas came from
   the IPng transition discussions in general, and there is a clear

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Draft         Address Extension by IP Option Usage (AEIOU) 21 March 1994

   resemblance to the DECnet Phase V deployment process.

   Various individuals have commented on the earlier versions of this
   document; a full list will be included in a future version.

Author's Address

       Brian E. Carpenter
       Group Leader, Communications Systems      Phone:  +41 22 767-4967
       Computing and Networks Division           Fax:    +41 22 767-7155
       CERN                                      Telex:  419000 cer ch
       European Laboratory for Particle Physics  E-mail:
       1211 Geneva 23, Switzerland

   Expires 26 September 1994

   File name draft-carpenter-aeiou-00.txt

Carpenter                                                       [Page 5]