distinction between users on different AP (talking to the same radius server)

K. Hoercher wbhoer at gmail.com
Sun Nov 19 13:10:05 CET 2006

On 11/19/06, liran tal <liransgarage at gmail.com> wrote:
> I'll try to elaborate on this...
> There are two access points deployed in two different locations, they both
> speak to a central radius sever,
> it looks like this:
> AP1 - DHCP Address Pool
> AP2 - DHCP Address Pool

ah ok. (nitpick: so the subnet mask /24 is not different, the subnets are *g*)

> Now, say user foo got connected to AP1, in the logs I will see he received
> FramedIPAddress
> so I will know for a fact that the user is conneccting from AP1 rather than
> AP2.

Which log? Again, as the issueing of dhcp leases would happen after
the associating/authenticating of the user's machine I would not
expect Framed-IP-Address  to be tranmitted in an Access-Request from
an ap to be acted on by freeradius. Actually the other way round would
be more common, freeradius sending that attribute to the ap. Maybe it
could be part of an accounting message sent by the ap, but that would
also be to late to base authentication decisions on in any sane way.

If you happen to have such setup nevertheless, could you show the
freeradius debug output?

> So I'm asking if there's a better way to do this rather than by configuring
> different subnets on the dhcp server of the APs.
> A NASIPAddress is actually a good solution but I'm not going with that cause
> I can't be sure that it's a static one (some APs
> receive their "wan" interface address by DHCP which may vary all the time).

Not freeradius related: Does every AP use/have its own dhcpd for the
users? If so, they should ensure that no confliciting leases get out
by means of relaying to a central server, coordinating between
themselves, assigning different ranges of ips or just keeping the
leases on different subnets (the last beeing not the best approach, I
think, and would also not be needed for freeradius as I tried to
explain already and will do, hopefully more completely, below).

Ok, so the mentioned combinations would include NAS-IP-Address to be
not part of them. I was talking in general about possible already
existing choices you could watch out for.

To do that even more: As to your wish to "distinct", what are your
needs related to that distinction:
authentication/authorization/accounting? As long as your aps send
anything as part of the radius protocol, which is specific to them
(which is quite probable) and known a priori (which might rule out
NAS-IP-Address, (but why not dhcping fixed addresses, or at least
different ranges to them? etc. as completely dynamic ips for aps look
a bit awkward to me, not only for the problem at hand))  in the
different messages to freeradius, that entitiy can be used (where/how
depends on the purpose) to decide between different alternatives.

> So any other ideas...

Not really, I would still uphold my statement previously made. To
perhaps clarify it a bit: Yes, of course you can configure freeradius
to act differently on different inputs. Any more specific suggestions
could only arise from you telling what the aps do (other than putting
users on different subnets, which is possible too, but not desireable
I think) ; more to the point: what (which attributes) do they send in
which situations, and what reaction you want in those situations.

K. Hoercher

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