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in eduroam, we are just about starting to make real use of the
Chargeable-User-Identity (RFC4372). Our motivation is not billing, but
being able to recognise fraudulent users when they return, to have a
means of permanently banning them. E.g. a user could change his MAC and
outer identity on every re-connect, and evade blocking measures if no
permanent opaque handle identifies him on return.
We are mostly happy with the RFC, but one of my colleagues stumbled upon
something. The RFC says that the business agreement between service
provider and home server determines the lifetime of a CUI. While that's
correct, there is a problem when intermediate proxies are involved (like
a clearing-house): since there is no reliable end-to-end identifier for
service providers, the home server may not know which business partner
it is talking to - it sees only the proxy's connection.
A concrete example from the RFC is: "For example, the lifetime can be
set to one billing period." A home server H doing business with two
service providers S1 (billing period: end of month), S2 (billing period:
25th of every odd month) via a proxy P would need to see an identifier
for S1, S2 when receiving Access-Requests from P to adjust the CUIs it
generates properly, and roll them over at the appropriate end of billing
There is not currently a standard attribute to convey this information.
NAS-IP-Address and NAS-Identifier are semantically bound to a single
NAS. A service provider can operate multiple NASes, on the same or
different access media.
I'm not sure if there is much to do about this. I suppose a good
real-life way to do this is to set a VSA with the information, and make
sure that P sets it for its customers. I wonder if it's worth defining a
properly standardised attribute for this though (since implementing
RFC4372 seems to implicitly require its existence)...
Ingenieur de Recherche
Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et de la Recherche
6, rue Richard Coudenhove-Kalergi
Tel: +352 424409 1
Fax: +352 422473
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