Network Working Group                                     net39-testgroup
INTERNET-DRAFT                                      bill manning - editor
Category: Informational                                     November 1995
Expires in six months

                       Class A Subnet Experiment
                       Results and Recommendations

Status of this Memo

        This documents the experience the Internet community with the
        Experimental Protocol defined in RFC 1797.  This does not specify
        an Internet standard of any kind.  Continued discussion is requested.
        Distribution of this memo is unlimited.

        This document is an Internet-Draft.  Internet-Drafts are
        working documents of the Internet Engineering Task Force
        (IETF), its areas, and its working groups.  Note that other
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        Internet-Drafts are draft documents valid for a maximum of six
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        To learn the current status of any Internet-Draft, please check
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        Shadow Directories on,,, or


        This memo documents some experiences with the RFC 1797[1] subnet A
        experiment and provides a number of recommendations on future
        direction for both the Internet Registries and the Operations

        Not all proposed experiments in RFC 1797 were done. Only the "case
        one" type delegations were made.  Additional experimentation was done
        within the DNS service, by supporting a root nameserver and the
        primary for the domain from within the subnetted address space.
        In addition, testing was done on classless delegation[2].

        Internet Services offered over the RFC 1797 experiment were:

                FTP server/client
                lpr (and its ilk)

        F.Root-Servers.Net, a root name server had an interface defined
        as part of the RFC 1797 experiment.  Attached is a report
        fragment on it's performance:

        "My root server has processed 400,000,000 queries in the last 38 days,
        and well over half of them were to the temporary address
        (note that I retained the old address since I knew a
        lot of folks would not update their root.cache files and I didn't
        want to create a black hole.)" - Paul Vixie

        Initial predictions[3] seemed to indicate that the safest path for
        an ISP that participates in such a routing system is to have -all-
        of the ISP clients be either:

                a) singly connected to one upstream ISP
                b) running a classless interior routing protocol

        It is also noted that a network with default route may not notice
        it has potential routing problems until it starts using subnets of
        traditional A's internally.

Problems & Solutions

        There were initial problems in at least one RIPE181[4] implementation.
        It is clear that operators need to register in the Internet
        Routing Registry (IRR) all active aggregates and delegations
        for any given prefix.  Additionally, there need to be methods
        for determining who is authoritative for announcing any given prefix.

        It is expected that problems identified within the confines of this
        experiment are applicable to some RFC 1597 prefixes or any "natural"
        class "A" space.

        Use of traceroute (LSRR) was critical for network troubleshooting
        during this experiment. In current cisco IOS, coding the
        following statement will disable LSRR and therefore inhibit
        cross-provider troubleshooting:

                no ip source-route

        We recommend that this statement -NOT- be placed in active ISP
        cisco configurations.

        In general, there are serious weaknesses in the Inter-Provider
        cooperation model and resolution of these problems is outside the
        scope of this document. Perhaps the IEPG or any/all of the national
        or continental operations bodies[5] will take this as an action
        item for the continued health and viability of the Internet.


        A classic cisco configuration that has the following statements

                ip route
                router bgp 64000
                redistribute static

        will, by default, promote any classful subnet route to a full
        classful route (supernet routes will be left alone).  This
        behaviour can be changed in at least the following two ways:

                ip route
                router bgp 64000
                no auto-summary
                redistribute static

                ip route
                router bgp 64000
                network mask
                redistribute static route-map static-bgp
                access-list 98 deny
                access-list 98 permit any
                route-map static-bgp
                match ip address 98

        Users of cisco gear currently need to code the following
        two statements:

                ip classless
                ip subnet-zero

        The implication of the first directive is that it eliminates
        the idea that if you know how to talk to a subnet of a network,
        you know how to talk to ALL of the network.

        The second is needed since it is no longer clear where the
        all-ones or all-zeros networks are[6].

        Other infrastructure gear exhibited similar or worse behaviour.
        Equipment that depends on use of a classful routing protocol,
        such a RIPv1 are prone to misconfiguration.  Tested examples
        are current Ascend and Livingston gear, which continue to
        use RIPv1 as the default/only routing protocol.  RIPv1 use
        will create an aggregate announcement.

        This pernicious use of this classful IGP was shown to impact
        otherwise capable systems.  When attempting to communicate
        between an Ascend and a cisco the promotion problem identified
        above, was manifest. The problem turned out to be that a classful
        IGP (RIPv1) was being used between the Ascends and ciscos.
        The Ascend was told to announce 39.1.28/24, but since RIPv1 can't
        do this, the Ascend instead sent 39/8.  We note that RIPv1, as
        with all classful IGPs should be considered historic.

        This validates the predictions discussed in [3].

Cisco Specific Examples

        There are actually three ways to solve the unintended aggregation
        problem, as described with current cisco IOS.  Which of them
        applies will depend on what software version is in the router.
        Workarounds can be implemented for ancient (e.g. 8.X) version software.

                o Preferred solution: turn on "ip classless" in the
                  routers and use a default route inside the AS.
                  The "ip classless" command prevents the existence of
                  a single "subnet" route from blocking access via the
                  default route to other subnets of the same old-style network.
                  Default only works with single-homed ISPs.

                o Workaround for 9.1 or later software where the
                  "ip classless" command is not available: install a
                  "default network route" like this:
                  "ip route <next-hop>" along the axis
                  the default route would normally take.  It appears
                  an ISP can utilize the "recursive route lookups" so
                  the "next-hop" may not actually need to be a directly
                  connected neighbour -- the internal router can e.g.
                  point to a loopback interface on the border router.
                  This can become "really uncomfortably messy" and it may
                  be necessary to use a distribute-list to prevent
                  the announcement of the shorter mask.

                o Workaround for 9.0 or older software: create a
                  "default subnet route": "ip route 39.x.y.0 <next-hop>"
                  combined with "ip default-network 39.x.y.0", otherwise
                  as the 9.1 fix.

        Both of the latter solutions rely on static routes, and in the
        long run these will be impossible to maintain.  In some
        topologies the use of static routes can be a problem (e.g. if there
        is more than one possible exit point from the AS to choose


        The RFC 1797 experiment appears to have been a success. We believe
        it safe to start carving up "Class A" space, if the spaces are
        delegated according to normal IR conventions[7] and recommend
        the IANA consider this for future address delegations.


        Thanks to all the RFC 1797 participants. Particular thanks to
        Paul Vixie, Geert Jan de Groot, and the Staff of the IETF33 Terminal
        room.  Other thanks to ACES, MCI, Alternet, IIJ, UUNET-Canada,
        Nothwestnet, BBN-Planet, cisco systems, RIPE, ESnet, Xlink,
        SURFnet, STUPI, Connect-AU, INBEnet, SUNET, EUnet, InterPath,
        VIX.COM, MindSpring.  Especial thanks to Suzanne for cleanup.


[1] IANA, "Class A Subnet Experiment", RFC 1797, ISI, April 1995
[2] H. Eidnes, G. J. de Groot, "Classless delegation",
    Work in Progress, SINTEF RUNIT, RIPE NCC, May 1995
[3] G. Huston, "Observations on the use of Components of the
    Class A Address Space within the Internet", Work in Progress,
    AARnet, May 1995
[4] T. Bates,, "Representation of IP Routing Policies
    in a Routing Registry", RFC 1786, MCI, March 1995
[5], November 1995
[6] F. Baker, Editor, "Requirements for IP Version 4 Routers", RFC 1812,
    cisco systems, June 1995
[7] K. Hubbard, M. Kosters, D. Conrad, D. Karrenberg, "INTERNET
    REGISTRY GUIDELINES", Work in Progress, InterNIC, APNIC, RIPE,
    November 1995

Security Considerations:

Security was not considered in this experiment.

Editor Address:

   Bill Manning
   Information Sciences Institute
   University of Southern California
   4676 Admiralty Way
   Marina del Rey, CA 90292-6695
   Phone: +1 310-822-1511 x387
   Fax:   +1 310-823-6714