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RIPE Recommendation: IP Networking On IXI

Publication date:
31 May 1991
  • T.Bates
  • M.Terpstra
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This paper gives a set of recommendations for the use of IP using the IXI
X.25 network, coordinated and supported by RIPE, the body that coordinates IP
activities in Europe. It will give recommendations on the usage of IXI for IP
activities as well as some guidelines on IP routing to the RIPE
infrastructure and the rest of the global Internet. A set of well managed and
well connected entry points into RIPE coordinated networks are proposed.
In this paper the phrase 'RIPE infrastructure' implies the infrastructure of
RIPE coordinated networks.


Since the introduction of the IXI infrastructure many of its Access Points
have expressed interest in the use of IP on this network. Connections
foreseen are inside IXI, between IXI and the European IP infrastructure and
the rest of the global Internet.
One of the major problems an X.25 network when used for IP can cause is the
set up of IP links from any access point to all of the other access points,
thus creating an increasingly unmanageable IP network consisting of
nn12 logical IP links.
This paper gives recommendations and guidelines to make proper use of
IXI for IP connectivity, and thus keep a manageable European IP

Entry Points into RIPE

Many of the IXI Access Points also make part of the RIPE infrastructure.
In principle all these IXI Access Points could be considered as
an entry point to the RIPE infrastructure.
As of today there exist 21 IXI Access Points into private academic and
research networks. This could in principle lead to an additional 210
international logical IP links in Europe. This would substantially increase
the existing complexity of IP routing in Europe. Managing such a complex IP
infrastructure would require a major effort in both manpower and money.
Therefore there should be a few well defined, well managed and well connected
entry points into the RIPE infrastructure for IP traffic over the IXI network.
Given the current and proposed topology of the RIPE infrastructure and the
current structure of the IXI network there is a certain overlap in topology.
Both infrastructures have major nodes in Switzerland and the Netherlands so it
seems logical to establish interconnections between the IXI and RIPE
infrastructures in Switzerland or the Netherlands.
One such an interconnection point is currently supported at NIKHEF (Amsterdam)
It is recommended that a similar interconnection point be established near
the IXI node in Bern (Switzerland).
It is also highly recommended that IXI participants wishing to connect
to the RIPE infrastructure are connected to IXI Access Points in Switzerland or
the Netherlands depending on their physical connection in the IXI network.
To keep these entry points well defined and well managed it is strongly
discouraged to connect to the RIPE infrastructure via other entry points than
the ones defined above. However, the number of entry points may be increased
if the traffic levels demand it. The obvious choice for extra IP over IXI
entry points would be KTH (Stockholm) and INFN (Bologna).
IXI participants connecting to above mentioned entry points will be given
equal technical support in their IP practices.

Routing issues

Routing within RIPE

If a simple set of entry points is adopted between the IXI access points
and the IP infrastructure then routing can be managed cleanly. The RIPE
routers use the RIPE database to control routes distributed among
the RIPE infrastructure.
Each IXI access point will have local routes for its own local IP networks and
will propagate them to their RIPE entry point. The RIPE entry point will
distribute all RIPE routes to the IXI access point router. The IXI
access point router is free to re-distribute the RIPE routes internally
but these routes MUST NOT be distributed to other RIPE entry points. The
distribution of RIPE networks is governed by the RIPE database entries.

RIPE access can be looked at from the IXI access points as one "Autonomous
System" even though technically it isn't. IXI access point routers should
peer with the RIPE entry point router using an "Exterior Routing Protocol"
probably EGP. However, due to limitations in routers it may be
more convenient to use an "Interior Routing Protocol" whereby the RIPE
entry point router can use a single routing process for all it's IXI access
points rather than separate ones.

Routing outside RIPE

If an IXI access point router has a need for connections outside of the
RIPE infrastructure (e.g. US internet) using IXI then the IXI access
point is free to establish an IP link to another IXI access point router.
However, RIPE received routes MUST NOT be re-distributed across this IP
link. Much care must be taken when setting and such a link and must
be co-ordinated with RIPE.


This section gives a set of recommendations or guidelines for the use of IP
on IXI. As stated in both IXI-CC and RIPE meetings, RIPE is the body that
coordinates IP activities in Europe, including IP activities on IXI, and is
willing to give technical support for IP activities on IXI.
The following recommendations follow from the above text or are
recommendations generally accepted by RIPE.

1 - Parties wishing to join the RIPE infrastructure with the use of IXI are
welcome and should contact the chairman of RIPE. They are however urged to
seek for connectivity on a regional or national level first.

2 - Parties wishing to join the RIPE infrastructure must give certain network
information for the RIPE database.

3 - The set up of IP links using IXI between parties already connected
through the RIPE infrastructure should not interfere with the current European
IP network practices.

4 - The set up of new IP links using IXI should be done in accordance with
the current and proposed topology of RIPE. This to avoid a spaghetti-like

5 - The routing of IP on IXI should be coordinated by RIPE or one of the
RIPE participants so as not to disturb the current routing in RIPE.

6 - Parties connecting to the RIPE infrastructure in other places than the
stated entry points should consider their link as local only, and no routes
using these links should be distributed to the RIPE infrastructure. It is
therefore strongly discouraged and should be used in exceptional cases only.

7 - The choice of location of well-known entry points for IP over IXI within
RIPE is dependent on some knowledge of the internals of the IXI network, e.g.
the location of the major switches and the topology of the links. It is a major
concern that this dependency exist, since changes in this area could have
serious consequences for services on the RIPE infrastructure.