|
In the normal case you describe below (where the NAS always
starts off with an EAP-Identity Request) there is no need for the NAS to ever
send an EAP-Start packet to the RADIUS server. This is only useful if the
Identity exchange might be superfluous and the RADIUS server can just start off
with the EAP method Request from the beginning. There are a very limited
number of situations where this would be useful because: a.
The NAS has to route the request to a RADIUS
server without a User-Name attribute because there has been no Identity
Exchange (e.g. only the Calling-Station-Id might be available to be placed in
the User-Name attribute) b.
The RADIUS server has to be prepared to
choose the EAP method based on what is placed in the User-Name attribute, if
anything. There are some limited situations in which this might be useful…
but I’m not aware of much deployment experience. The EAP-Start packet is a RADIUS Access-Request packet
containing an EAP-Message attribute with a single NUL character. So the
length of the EAP-Message attribute is >=3. Might make sense to file an errata to clarify. There is no RADIUS attribute to encapsulate EAPoL, only
EAP-Message, which is used to encapsulate EAP. So there is no way
to send an EAPoL-Start packet to a RADIUS server within an EAP-Message
attribute. If there is a need to convey EAPoL-Start data (e.g. IEEE
802.1X-REV extensions to EAPoL-Start such as NIDs) then you’d need to define a
distinct RADIUS attribute to convey that. From: Koehler, Yannick
[mailto:yannick.koehler@hp.com] Hello, I have read the RFC 3579 and I have some questions
and I was hoping to get some answers from you. In the RFC it says that
the EAP-Start may be represented by an EAP-Message of length 2 (no data).
Yet, the specification of this EAP-Message attribute is defined with a
length >= 3 and that, even in the RFC 3579. Also, I do not follow why
there is an EAP-Start packet is this the same as EAPOL-Start ? And if
not, why sending such an empty packet to a RADIUS server? It seems to me
like it waste a round-trip. My understanding of 802.1x nego is something like
that: Client sends EAPOL-Start
NAS answer EAP-Identity Request Client sends EAP-Identity response
NAS sends RADIUS with EAP identity response to RADIUS
RADIUS reply
NAS forward answer. Client continue exchange. How is the EAP-Start affecting this negotiation and when is
it used, and why? Is there more documentation on this packet? -- Yannick Koehler |