An Experiment in DNS Based IP Routing
RFC 1383

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Network Working Group                                         C. Huitema
Request for Comments: 1383                                         INRIA
                                                           December 1992

                 An Experiment in DNS Based IP Routing

Status of this Memo

   This memo defines an Experimental Protocol for the Internet
   community.  Discussion and suggestions for improvement are requested.
   Please refer to the current edition of the "IAB Official Protocol
   Standards" for the standardization state and status of this protocol.
   Distribution of this memo is unlimited.

Table of Contents

   1. Routing, scaling and hierarchies ......................    1
   2. Routing based on MX records ...........................    2
   3. Evaluation of DNS routing .............................    3
   3.1 Loops and relays .....................................    4
   3.2 Performances and scaling .............................    5
   3.3 Tunneling or source routing ..........................    6
   3.4 Choosing a gateway ...................................    6
   3.5 Routing dynamics .....................................    6
   3.6 DNS connectivity .....................................    7
   3.7 On the way back ......................................    8
   3.8 Flirting with policy routing .........................    8
   4. Rationales for deployment .............................    9
   4.1 The good citizens ....................................   10
   4.2 The commercial approach ..............................   10
   5. The experimental development ..........................   11
   5.1 DNS record ...........................................   11
   5.2 Interface with the standard IP router ................   12
   5.3 The DNS query manager ................................   12
   5.4 The real time forwarder ..............................   12
   5.5 Interaction with routing protocols ...................   13
   6. Acknowledgments .......................................   13
   7. Conclusion ............................................   13
   8. References ............................................   14
   9. Security Considerations ...............................   14
   10. Author's Address .....................................   14

1.  Routing, scaling and hierarchies

   Several recent studies have outlined the risk of "routing explosion"
   in the current Internet: there are already more than 5000 networks
   announced in the NSFNET routing tables, more than 7000 in the EBONE

Huitema                                                         [Page 1]
RFC 1383                  DNS based IP routing             December 1992

   routing tables.  As these numbers are growing, several problems
   occur:

      *    The size of the routing tables grows linearly with the
           number of connected networks; handling this larger tables
           requires more resources in all "intelligent" routers, in
           particular in all "transit" and "external" routers that
           cannot rely on default routes.

      *    The volume of information carried by the route exchange
           protocols such as BGP grows with the number of networks,
           using more network resources and making the reaction to
           routing events slower.

      *    Explicit administrative decisions have to be exercised by
           all transit networks administrators which want to
           implement "routing policies" for each and every
           additional "multi-homed" network.

   The current "textbook" solution to the routing explosion problem is
   to use "hierarchical routing" based on hierarchical addresses. This
   is largely documented in routing protocols such as IDRP, and is one
   of the rationales for deploying the CIDR [3] addressing structure in
   the Internet. This textbook solution, while often perfectly adequate,
   as a number of inconveniences, particularly in the presence of
   "multihomed stubs", e.g., customer networks that are connected to
   more than one service providers.

   The current proposal presents a scheme that allows for simple
   routing. It is complementary with the classic "hierarchical routing"
   approach, but provides an easy to implement and low cost solution for
   "multi-homed" domains. The solution is a generalization of the "MX
   record" scheme currently used for mail routing.

2.  Routing based on MX records

   The "MX records" are currently used by the mail routing application
   to introduce a level of decoupling between the "domain names" used
   for user registration and the mailbox addresses. They are
   particularly useful for sending mail to "non connected" domains: in
   that case, the MX record points to one or several Internet hosts that
   accept to relay mail towards the target domain.

   We propose to generalize this scheme for packet routing.  Suppose a
   routing domain D, containing several networks, subnetwork and hosts,