Description of Inter-AS Networks in the RIPE Routing Registry

Friends,

here is the proposal on how to solve the prtraceroute problem as
discussed in the last routing-WG meeting. Could we have comments until
May 17th please! I'll circulate new versions as substantive comments
are incorporated. The goal is to have the database capable of storing this
a.s.a.p. and have some data in there quickly as prtraceroute is released.

Note that this is not only useful for prtraceroute but much more generally.
It could also be the start of the local inter-AS connection information 
dicussed in the last routing-wg meeting too. As such this addendum could
be extended. Proposals ?

Cheers

Daniel






        Description of Inter-AS Networks in the RIPE
                      Routing Registry



                         Tony Bates
                     Daniel Karrenberg

                        Addendum to
           Representation of IP Routing Policies
               in the RIPE Database (ripe-81)





What is an Inter-AS Network ?

Inter-AS IP networks are those networks which connect multi-
ple autonomous systems (1).  An inter-AS network exists  for
the  purpose  of  passing  traffic  and  routing information
between different autonomous systems.  The most simple exam-
ple  of  an  inter-AS network is a point-to-point link, con-
necting exactly two ASes.  Each end of such a link  is  con-
nected to an interface of router living in each of the auto-
nomous systems. More complex  examples  are  broadcast  type
networks  with  multiple interfaces connecting multiple ASes
with the possibility of more than one connection per AS.


Which additional information is needed?

Consider the following example of three routers 1, 2  and  3
with  interfaces a through f  connected by two inter-AS net-
works X and Y:


         X              Y
a1b     ---    c2d     ---    e3f







_________________________
(1) Inter-AS networks are currently called FIXes, IXFs,
DMZs, NAPs, GIX and other names.
                           - 2 -


Suppose that network X is registered in the routing registry
as  part  of AS1 and net Y as part of AS3. If traffic passes
from left to right prtraceroute will  report  the  following
sequence of interfaces and ASes:

        a in AS1
        c in AS1
        e in AS3

The  traceroute  algorithm  enumerates  only  the  receiving
interfaces  on  the  way to the destination.  In the example
this leads to the passage of AS2 going unnoticed.   This  is
confusing to the user and will also generate exceptions when
the path found is checked against the routing registry.


For operational monitoring tools such as prtraceroute it  is
necessary  to  know  which  interface on an inter-AS network
belongs to which AS.  If AS information is not  known  about
interfaces  on  an inter-AS network, tools like prtraceroute
cannot determine correctly which ASes are being traversed.


Proposed Format

All interfaces on inter-AS networks will be described  in  a
new ias-int attribute of the corresponding network object in
the RIPE database.  The ias-int attribute has the  following
syntax:

ias-int:   <interface-address> <autonomous-system>


The  <interface-address>  must  be  an  address  within  the
corresponding intenum and <autonomous-system> must be of the
form AS<number> refering to an aut-num object in  the  data-
base.
                           - 3 -



For example:

inetnum:   193.193.193.0
netname:   INTER-AS-EXAMPLE
descr:     This is a hypothetical inter-as network.
descr:     It might be called a NAP, FIX, GIX, IXF, DMZ,
descr:     Mehrfachdienstanbieterkommunikationseinrichtung or ...
country:   DE
admin-c:   Werner Mueller
tech-c:    Paul Schmitz
tech-c:    Hans Meier
changed:   ripe-dbm at ripe.net 920714
aut-sys:   AS4711
ias-int:   193.193.193.1 AS123
ias-int:   193.193.193.3 AS4711
ias-int:   193.193.193.9 AS789
source:    RIPE

Note that the interface 193.193.193.3 is described  although
it  is  in  the same AS as the network.  This is recommended
practice.


The update procedure for the ias-int attribute will  be  the
normal  update procedure for network objects.  The attribute
does not need to be guarded because it  does  not  influence
routing policy of operational traffic.



In which AS does an Inter-AS Network belong?

Only one AS announces an inter-AS network  externally.   The
other  ASes  connected to the inter-AS network will probably
carry this network in their internal routing for  redundancy
but will not announce it to other ASes.

In exceptional cases more than one AS may need to  originate
external  routing  information  about  the inter-AS network,
This kind of routing setup cannot be  described  within  the
framework  of  ripe-81  and is generally discouraged.  Tools
using a ripe-81 type registry  could  take  heuristic  hints
from  the ias-int attributes when they encounter such situa-
tions.