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AAA Routing with EAP-ER



Working on
http://tools.ietf.org/wg/dime/draft-dondeti-dime-erp-diameter-01.txt
the question of defining AVPs vs. defining a new Diameter application showed up.

I wrote a section about this into that draft and I wonder whether my assumptions are reasonable:

3.  Assumptions

  This document defines additional optional AVPs for usage with the
  Diameter EAP application.  Routing of these messages is therefore
  provided via the Diameter Application Identifier (among other
  elements), as specified by the Diameter Base protocol [4].  Based on
  the deployment of ERP, a local Diameter server (the same entity
  serves as a Diameter proxy during the full EAP authentication) may
  play the role of the ER server for future re-authentication attempts.
  As such, the local Diameter server requesting the DSRK needs to be in
  the path of the current EAP exchange between the peer and the EAP
server and also along the path in the future. The Diameter client is furthermore assumed to be able to route the re-authentication messages to the ER server.


Depending on some of the answers to the questions raised in this discussion it might be necessary to define a new Diameter application rather than just defining new AVPs.

Ciao
Hannes


Bernard_Aboba@hotmail.com wrote:
When the peer, the local domain and the AAA-Home also
support ERP, a DSRK (DSRK1) may be requested by the local ER server A at
the time of the EAP exchange.

Some questions:

1. Is the "Local ER server" always a RADIUS client? The ERX document seems to
indicate that this might not always be the case.

2. How is the request for the DSRK made by the "local ER server"? Is the
request authenticated with user credentials?  How does the RADIUS server
determine if the Request is valid?

3. How does the RADIUS server know how to reach the "Local ER server"?
The ERX document talks about a "Domain Identity". How does the RADIUS server use the "Domain Identity" to determine what RADIUS client to send a packet to? Is there an assumption that the "Local ER server" is one hop away from the home RADIUS server? What attributes need to be placed within an Access-Accept
to ensure that the packet is routed to the "local server"?

4.  In Figure 1, the ERX document shows the following flow:

   [<-- EAP-Request/ ------
       Identity]
   [<-- EAP Initiate/ ------
       Reauth-Start]

Is this a typo? The figure shows that the EAP-Request/Identity isn't being responded to by the peer. If the peer implements RFC 3748, won't it send an EAP-Response, which will be passed to the RADIUS server, which will then initiate EAP? Figure 1
seems to show the EAP peer ignoring the EAP-Request, which
implies that it needs to wait for some period of time for another message, which
might or might not arrive.   How long should it wait?

If the peer doesn't respond to the EAP-Request/Identity, according to RFC 3748 and RFC 4137, the NAS will retransmit. So we'll have two EAP conversations
going on at once?

5. In Figure 2, the peer is initiating what would appear to be a standard
RADIUS/EAP conversation via the EAP-Response/Identity.   However, it
would appear that the EAP Response/Identity is being "augmented" by
the local server.  It's hard for me to tell from the figure whether the
[DSRK Req, Domain Identity] is being inserted within the EAP-Response/Identity,
or whether it represents separate RADIUS attributes.  Can you clarify?

6. If the "local 'server" isn't on the path between the NAS and the home server (as it might not be, because of failover), what happens? Does each proxy
also need to host a "local server" to make sure that doesn't occur?
If the "local server" is not on the path, then it seems like two distinct messages would be required. Is there an expectation that the RADIUS Access-Accept
will be multicast, or that two distinct RADIUS Access-Accept packets will
be sent?






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