Description of Inter-AS Networks in the RIPE Routing Registry Tony Bates Daniel Karrenberg Document-ID: ripe-103 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 multiple auto- nomous systems (1). An inter-AS network exists for the purpose of passing traffic and routing information between different autonomous systems. The most simple example of an inter-AS network is a point-to-point link, connecting exactly two ASes. Each end of such a link is connected to an interface of router living in each of the autonomous systems. More complex examples are broadcast type net- works with multiple interfaces connecting multiple ASes with the possibility of more than one connection per AS. _________________________ (1) Inter-AS networks are currently called FIXes, IXFs, DMZs, NAPs, GIX and other names. ripe-103.txt December 3, 1993 - 2 - 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 networks X and Y: X Y a1b --- c2d --- e3f 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 pas- sage 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 neces- sary 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. Routing Registry Format All interfaces on inter-AS networks will be described in a new ias- int attribute of the corresponding network object in the RIPE data- base. The ias-int attribute has the following syntax: ias-int: The must be an address within the corresponding intenum and must be of the form AS referring to an aut-num object in the database. ripe-103.txt December 3, 1993 - 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@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 opera- tional 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 net- work 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 situations. ripe-103.txt December 3, 1993