Subject: [Sidr] other means of trusting announcements

From: Joe Abley <[email-masked]>
Date: Wed, 20 Jun 2007 22:07:27 -0400

Hi all,

I made a comment during the wg meeting in Prague in response to a  
question from the floor (I forget who asked the question; someone  
from Easynet, I think). Sandy and Steve asked me to repeat it on the  
list.

The problem at the time, if I remember correctly, was one of context.  
For many operators in the RIPE region, there is established practice  
for building filters automatically for use as import filters on BGP  
sessions which is common to many operators. In that context, the SIDR  
approach as described in the face-to-face meeting is perplexing. It  
may well be that the documents could benefit from some accommodation  
of this context in the interests of rapid comprehension by operators  
in that region (operators who, I think, have shown the most interest  
in applying import filters to peers and customers).

The RPSL repository operated by the RIPE NCC (the "RIPE database") on  
behalf of RIPE members (and others) incorporates a feature which I  
believe is not available in corresponding services offered by other  
RIRs. The assignment/allocation data from the RIR (in the form of  
RPSL inetnum, aut-num, etc objects) is linked for the purposes of  
authentication with routing data (e.g. route, route6, etc objects).

This linkage is provided by RPSS (Routing Policy System Security).  
RPSS is documented in RFC 2725, but I do not know how accurate that  
document is with respect to the code which is actually running today  
in Amsterdam.

In broad terms (and apologies to those who know the details of this,  
and who are now cringing) it is not possible to register a route  
object in the RIPE database if you are not authorised to manipulate  
the corresponding (covering) inetnum object. This means that the  
presence of a route object with a particular origin attribute implies  
reasonable confidence that the AS specified in the origin is  
authorised to originate the route in question.

[The big hole in this trust dynamic is that for addresses assigned by  
other RIRs, no such linkage exists; in practice anybody can install  
route objects for addresses they have no business announcing in the  
RIPE database so long as those route objects don't already exist, and  
so long as the addresses concerned are not taken from one of the RIPE  
NCC's pools.]

The key point is that it is possible to build a prefix filter based  
on policy expressed in an aut-num or as-set RPSL object using the  
RIPE database and have a reasonable degree of confidence that the  
resulting prefix filter is probably a reasonable one, at least if the  
peers you mainly deal with are European, and acquired their addresses  
from the RIPE NCC.

For an operator in Europe who mainly deals with other European  
networks, it may well appear that confidence in the origination of a  
particular route from a particular AS is a problem which is largely  
solved. In this context, the need for the X.509 approach developed in  
this working group seems unclear, and the practical process by which  
a prefix filter could be constructed with reference to a certificate  
chain is non-obvious.

For operators elsewhere there is no such context, and the idea of a  
solution to the problem "how do I trust this new customer when he  
says he is allowed to announce route X through me" that doesn't  
involve photoshopped letterheads and fax machines is no doubt much  
more obviously attractive.

Joe

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