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

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 possible.

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 better.

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 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 different.

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 destination.

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 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 datagram.
  • 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 deployed.
  • 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.

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