RFC 1383 (rfc1383) - Page 3 of 14

An Experiment in DNS Based IP Routing

RFC 1383                  DNS based IP routing             December 1992


   and I2 --. These gateways also have a particularity: they retain
   information, and don't try to announce to the Internet any
   reachibility information on the networks contained within "D". These
   networks however have been properly registered; a name server
   accessible from the Internet contains the "in-addr.arpa" records that
   enable reverse "address to name" lookup, and also contains the
   network level equivalent of "MX records", say "RX records". Given any
   host address Dx within D, one can get "RX records" pointing to the
   Internet addresses of the gateways, I1 and I2.

   A standard Internet router Ix cannot in principle send a packet to
   the address Dx: it does not have any corresponding routing
   information. However, if the said Internet router has been modified
   to exploit our scheme, it will query the DNS with the name build up
   from "Dx" in the "in-addr.arpa" domain, obtain the RX records, and
   forward the packet towards I1 (or I2), using some form of "source
   routing". The gateway I1 (or I2) will receive the packet; its routing
   tables contain information on the domain D and it can relay the
   packet to the host Dx.

   At this stage, the readers should be convinced that we have presented
   a scheme that:

      *    avoid changes in host IP addresses as topology changes,
           without requiring extra overhead on routing (provided
           that the routing employs some form of hierarchical
           information aggregation/abstraction),

      *    allow to support multihomed domains without requiring
           additional overhead on routing and without requiring
           hosts to have explicit knowledge of multiple addresses.

   They should also forcingly scratch their head, and mumble that things
   can't be so simple, and that one should perhaps carefully look at the
   details before assuming that the solution really works.

3.  Evaluation of DNS routing

   Several questions come to mind immediately when confronted to such
   schemes:

       -    Should all relays access the DNS? What about possible
            loops?

       -    Will the performances be adequate?

       -    How does one choose the best gateway when several are
            announced? What happens if the gateway is overloaded, or



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