Network Working Group                                          R. Hinden
Request for Comments: 1955                        Ipsilon Networks, Inc.
Category: Informational                                        June 1996

    New Scheme for Internet Routing and Addressing (ENCAPS) for IPNG

Status of This Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.


   This document was submitted to the IETF IPng area in response to RFC
   1550.  Publication of this document does not imply acceptance by the
   IPng area of any ideas expressed within.  Comments should be
   submitted to the mailing list.

   This memo describes a proposal made to to the Routing and Addressing
   group [ROAD] January 1992 by Robert Hinden.  It was originally sent
   as an email message.  It proposes a medium term solution to the
   Internet's routing and addressing problems.


   I would like to propose a new scheme which I believe is a good medium
   term solution to the routing and address problems of the internet.
   It has the following positive attributes:

      - No Changes to Hosts
      - No Changes to Most Routers
      - No New Routing Protocols
      - No New Internet Protocols
      - No Translation of Addresses in Packets
      - Reduces the Routing Table Size in All Routers
      - Uses the Current Internet Address Structure

   It is not a solution good for all time, because it does impose some
   size limits and does not support new internet services such as
   guaranteed bandwidth, delay, etc.  It does require border routers to
   do additional processing, but does not require any packet
   translation.  I believe that this scheme will give us enough time to
   put into place a long term solution (i.e. pick one or more of CLNP,
   *NAT, IDPR, IDRP, Nimrod, Unified, NewIP, etc.)

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RFC 1955                       IP Encaps                       June 1996

   This scheme is based on the ideas presented by Deborah Estrin (route
   on ADs), Martha Steenstrup (encapsulation), and probably steals from
   ideas put forward by Noel Chiappa, Van Jacobson , Ross Callon, Dave
   Oran, and everyone else in the ROAD group.


   I think that we (the ROAD group) agree that in the short term we need
   to make better use of the IP address space.  I think we also (mostly)
   agree that in the long term we need a solution that can deal with a
   very large number of end points and routes, as well as support new
   services such as guarantees of service, source selected routes, etc.
   We do not agree on any of the details of this but do agree that we
   can not figure out a long term solution before March.  We do agree
   that we should start working on a long term solution(s).

   What this leaves is the need for a good medium term solution which
   can keep the Internet going until we can design and deploy a long
   term solution.  The medium term solution wants to be the most "cost
   effective".  It should buy us the most time to develop a long term
   solution and do it with as little change to the existing Internet as

   I propose this scheme as a new medium term solution.


   The basic idea is that inter-domain routing be done by routing on
   autonomous domains (AD).  The key is how this is done.  The mechanism
   to do this is for the border routers to encapsulate the original IP
   datagrams with another IP header.  The source and destination
   addresses in the new header (I will call it the AD-Header from here
   on) represent the source and destination ADs.

   When the first (entrance) border router receives a datagram from a
   host or router without an AD-Header it looks at the source and
   destination address and does a DNS lookup to get the addresses for
   the AD-Header.  It then adds an AD-Header and forwards the
   encapsulated datagram to its proper destination AD.

   The border routers would compute AD routes by running a routing
   protocol between themselves.  BGP or even IS-IS or OSPF for that
   matter, would work fine.  As you will see later, they might even be

   The addresses I propose to use for the AD addresses are plain old IP
   addresses.  A small number of Class A and Class B addresses would be
   reserved for this purpose.  The network number of the address would

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RFC 1955                       IP Encaps                       June 1996

   indicate that it was an AD identifier.  The local part of the address
   would indicate the actual AD.  This would allow for many ADs to be
   supported.  For example, 10 Class-A and 10 Class-B addresses could
   accommodate (10*2^24 + 10*2^16) 168,427,500 ADs.  We clearly don't
   need that many for a long time.

   The reason why I would chose to get more than one network number to
   use to represent the AD address is I would use them to organize the
   ADs.  Let's call them commonwealths.  Each commonwealth would only
   have to know the detail of it's own ADs.

   Next I would have the border routers inject these AD addresses into
   the Intra-AD routing of transit ADs.  They would tell the routers
   inside of the transit AD that they (the border routers) were the
   route to each appropriate AD network.  Commonwealths that have
   multiple interconnects (probably the common case) could by the use of
   careful assignment of the AD addresses use subnetting to support
   reasonable routing between the commonwealths.  This is where OSPF or
   IS-IS might be better than BGP.  Also, IS-IS, with its ability to
   route on actual end points might be the best.

   The motivation behind injecting the AD addresses into the Intra-AD
   routing of the transit ADs, is that the routers in these ADs can
   forward the AD-Headers without knowing that they are special.  Only
   the entrance and exit border routers are required to do anything

   Finally when a AD-Header is received at the last (exit) border router
   it strips off the AD-Header and sends the datagram to the final

   This scheme is based around the idea that IP addresses are globally
   unique.  I think that we will not actually run out of IP addresses
   for a long time and that we can live with the current addressing
   until we can deploy a long term solution.

   This scheme could be extended to not require globally unique IP
   address.  Effectively the combination of AD-Address and IP-Address is
   the globally unique address.  To use this scheme without globally
   unique IP-Addresses and without changing in the hosts would require a
   NAT mechanism in the border routers.  I think it would be preferable
   to change the hosts to have them do the DNS query and add the AD-
   header.  This could be the basis for the long term solution.

   Another interesting aspect of this scheme is that if we were to relax
   the current architecture where one IP-Address is always in only one
   AD, to allow an IP-Address to be in more than one AD, it would
   provide a solution to the issue of allowing a IP entity to get

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RFC 1955                       IP Encaps                       June 1996

   service from more than one service provider.


   The DNS needs to be extended to add an AD-Address entry for each
   name.  These will be used by the entry and exit border routers to get
   the AD-Addresses to use when building the AD-Headers.

   Border routers need to be extended to do the DNS lookup, perform AD-
   Header encapsulation, run an inter-AD routing algorithm using AD-
   Addresses, and be able to AD-Header de-encapsulation.


   I believe that this scheme has may advantages.  These are:

      - Only border routers and the DNS need change.  No changes are
        required in hosts or non-border routers.

      - No performance impact on datagram forwarding except at entry
        and exit border routers.

      - Only a small impact on bandwidth utilization on transit
        networks due the addition of a 20 byte IP header to each

      - Removes the Inter-AD routing from Intra-AD routing and as a
        result solves the routing load (table size and computation)
        problem for the foreseeable future.

      - The routing load on the border routers is manageable because
        border routers only need to know the detail of the routing
        commonwealth they are a member of.  Other commonwealths appear
        as single addresses.

      - No requirement for new routing protocols to be designed or

      - No translation of packets from one address scheme to another.

      - Uses the current IP addressing structure.

      - It scales well even if there is on the order of one AD per IP
        network, because the AD-Addresses can be assigned logically.

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RFC 1955                       IP Encaps                       June 1996

   It does have some disadvantages.  These are (at least):

      - It is not a long term solution in its initial form.

      - It assumes that the current IP-Addresses can remain globally
        unique for a long time.


   [ROAD] Gross, P., and P. Almquist, "IESG Deliberations on Routing
          and Addressing", RFC 1380, ANS, Stanford University,
          November 1992.


   Security issues are not discussed in this memo.


   Robert M. Hinden
   Ipsilon Networks, Inc.
   2191 East Bayshore Road
   Suite 100
   Palo Alto, CA 94303

   Phone: +1 (415) 846-4604

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