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Network Working Group net39-testgroup
Request for Comments: 19xx bill manning - editor
Category: Experimental November 1995
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.
Discussion/Purpose
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
community.
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:
Finger
HTTP
Telnet
FTP server/client
Gopher
DNS
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 39.13.229.241 address
(note that I retained the old 192.5.5.241 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
OR
b) running a classless interior routing protocol
Problems & Solutions
Operations
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.
Routing
A classic cisco configuration that has the following statements
ip route 39.1.28.0 255.255.255.0
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:
1:
ip route 39.1.28.0 255.255.255.0
router bgp 64000
no auto-summary
redistribute static
2:
ip route 39.1.28.0 255.255.255.0
router bgp 64000
network 39.1.28.0 mask 255.255.255.0
redistribute static route-map static-bgp
....
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 39.0.0.0 255.0.0.0 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.
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
from).
Recommendations:
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.
Credits:
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.
References:
[1] IANA, "Class A Subnet Experiment", RFC 1797, ISI, April 1995
[2] H. Eidnes, G. J. de Groot, "Classless in-addr.arpa 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, et.al, "Representation of IP Routing Policies
in a Routing Registry", RFC 1786, MCI, March 1995
[5] http://info.ra.net/div7/ra/Ops.html, 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
USA
Phone: +1 310-822-1511 x387
Fax: +1 310-823-6714
EMail: [email protected]
--
--bill
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