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Update blocks and simple conditions

Goal: Explore uses of update blocks in the policy language

Time: 10-25 minutes

File:

  • sites-available/default

man page: unlang

documentation page(s):

For this tutorial you should start with an empty authorization section (recv Access-Request { …​ } or in ≤ v3.2.x authorize { …​ }) in the virtual server you’re using to process requests.
Common control attributes

Attributes in the &control list can control the behaviour of the server. Commonly used control attributes are:

  • &control.Auth-Type specifies the authenticate <name> {} section to run

Unlang update blocks are used to update one or attributes in one of the server’s attribute lists.

In previous tutorials we’ve used the files modules, and the authorize methods of authentication modules such as pap and chap to alter how the server processes requests by setting a Auth-Type value. Here, we will emulate that behaviour using the policy language.

  • Create a condition (condition 1) to execute policy code if the &User-Name in the request is 'bob'.

  • Within that condition block, set the control attribute &Password.Cleartext to be 'hello', and instruct the server to run the the authenticate { …​ } subsection for pap.

  • Use the bob.sh script to verify that you see an Access-Accept returned despite the files module not being called.

Using additional conditions and update blocks, emulate the logic implemented using the files module in the Matching Users exercise.

To recap:

  • If an incoming request contains a &User-Name attribute with the value 'bob', and contains and attribute &Framed-Protocol with value PPP (condition 2), reply with a &Framed-IP-Address attribute with the value 192.168.10.12.

  • If an incoming request contains a &Service-Type attribute with a value of Framed-User (condition 3), reply with a &Framed-Route attribute assigning a default route of 192.168.10.1 (0.0.0.0/0 192.168.10.1 1) and a &Framed-IP-Netmask attribute with a value of 255.255.255.0.

Again test the server with username "bob" and password "hello". Use the debug output of the server to see which unlang conditions evaluated to true. You may use radclient or the bob.sh script to send the packets.

Perform other authentication tests, adding the appropriate attributes to the test requests to exercise the different conditions. If you already have test packets from the Matching Users exercises, you may use those, otherwise continue until you have packets that will match:

  • conditions 1 and 2, but not 3.

  • conditions 1 and 3, but not 2.

  • conditions 1, 2, and 3.

Questions

  1. What are the advantages of unlang over the files module when creating policies?

  2. What are the advantages of the files modules over unlang? Are there any situations where you think the files module might be better suited to a task than unlang?

  3. Can you think of any efficiencies the users module might have over multiple conditions, where policies are being assigned to many different users?