[Kea-users] Need help assigning subnets by class with host reservations

Thomas Markwalder tmark at isc.org
Thu Nov 10 14:12:26 UTC 2016

On 11/9/16 2:28 PM, mrobti at insiberia.net wrote:
> On 2016-11-09 07:56, Thomas Markwalder wrote:
>> On 11/9/16 4:20 AM, mrobti at insiberia.net wrote:
>>> On 2016-11-08 15:44, mrobti at insiberia.net wrote:
>>>> I want to assign a client-class using hwaddr, from MySQL backend, and
>>>> restrict a subnet for that client-class. In other words, only allow
>>>> clients with known MAC addresses to use the subnet they are trying to
>>>> connect to.
>>>> DB hosts table has an entry for the client:
>>>> dhcp4_subnet_id = 1
>>>> dhcp_identifier_type = 0
>>>> dhcp_identifier = UNHEX(REPLACE('aa:bb:cc:dd:ee:ff', ':', ''))
>>>> hostname = test.local
>>>> dhcp4_client_classes = test_class
>>>> Config file has:
>>>> "client-classes": [ {
>>>>   "name": "test_class"
>>>> } ],
>>>> "subnet4": [ {
>>>>   "id": 1,
>>>>   "subnet": "",
>>>>   "pools": [ { "pool": " -" } ],
>>>>   "client-class": "test_class"
>>>> } ],
>>>> But Kea says (debug level 50):
>>>> : client packet has been assigned to the following class(es):
>>>> : failed to select subnet for the client
>>>> : no suitable subnet configured for a direct client
>>>> It works if I remove "client-class" from the subnet definition, so
>>>> something is not synchronizing the class somewhere.
>>>> Could it be a problem that the DB hosts entry has no ipv4_address
>>>> listed? (that column is NULL)  I don't have any other ideas.
>>> I've found this in the logs:
>>> : HOSTS_CFG_GET_ALL_IDENTIFIER get all hosts with reservations using
>>> identifier: hwaddr=aa:bb:cc:dd:ee:ff
>>> hwaddr=aa:bb:cc:dd:ee:ff, found 0 host(s)
>>> Why would this happen? Yes, I double checked the MAC address. I
>>> enabled MySQL logging, and I can't match up timestamps exactly, but I
>>> do find a query:
>>> SELECT host_id, dhcp_identifier, dhcp_identifier_type,
>>> dhcp4_subnet_id, dhcp6_subnet_id, ipv4_address, hostname,
>>> dhcp4_client_classes, dhcp6_client_classes FROM hosts WHERE
>>> dhcp4_subnet_id = ? AND dhcp_identifier_type = ?    AND
>>> dhcp_identifier = ?
>>> I don't know if it's possible to see the executed version of this
>>> prepared query(?). Is it possible that the value Kea is placing in the
>>> query is not the correct binary string?
>>> _______________________________________________
>>> Kea-users mailing list
>>> Kea-users at lists.isc.org
>>> https://lists.isc.org/mailman/listinfo/kea-users
>> Hello:
>> We are looking into this for you.  As you probably know,  Kea will look
>> first for hosts defined its configuration file and then within the hosts
>> database (if it is specified).  Any log statements you see that contain
>> "HOSTS_CFG_" pertain to looking at hosts defined via the configuration
>> file.  In your case, since there are none, you see none found.  When Kea
>> accesses the host database the logs should contain
>> HOSTS_MGR_ALTERNATIVE_.   The following is a snippet from of the log in
>> a setup I am testing with:
>> 2016-11-09 10:18:45.018 DEBUG [kea-dhcp4.hosts/24940]
>> HOSTS_CFG_GET_ONE_SUBNET_ID_ADDRESS4 get one host with reservation for
>> subnet id 1 and IPv4 address
>> 2016-11-09 10:18:45.018 DEBUG [kea-dhcp4.hosts/24940]
>> HOSTS_CFG_GET_ALL_ADDRESS4 get all hosts with reservations for IPv4
>> address
>> 2016-11-09 10:18:45.018 DEBUG [kea-dhcp4.hosts/24940]
>> HOSTS_CFG_GET_ALL_ADDRESS4_COUNT using address, found 0
>> host(s)
>> 2016-11-09 10:18:45.018 DEBUG [kea-dhcp4.hosts/24940]
>> HOSTS_CFG_GET_ONE_SUBNET_ID_ADDRESS4_NULL host not found using subnet id
>> 1 and address
>> 2016-11-09 10:18:45.018 DEBUG [kea-dhcp4.hosts/24940]
>> HOSTS_MGR_ALTERNATE_GET4_SUBNET_ID_ADDRESS4 trying alternate source for
>> host using subnet id 1 and address
>> The last log statement indicates that Kea is looking in MySQL for hosts
>> that have the allocated address.  It just so happens that Kea actually
>> conducted a search in MySQL prior to the last one show above.  This
>> search is done by subnet id and dhcp identifier.   However the function
>> that performs this search happens to be missing a log entry.  This is
>> why you see  the two selects  you cited in the MySQL log but only one
>> log message against the alternate.   The original function we used
>> was deprecated without the new one getting a log message.  Sorry about
>> that.
>> On the surface, it looks like Kea should be matching your host, we're
>> still researching it.  You might try defining your host in the
>> configuration file, for testing purposes.   Do you have a packet capture
>> and what version of Kea are you running?
> Thank you for your response. I don't have a packet capture at the
> moment, but I do see the HOSTS_MGR_ALTERNATE_ line just like yours.
> I'm running the ubuntu package which shows version 1.0.0, the package
> name is version 1.0.0-1build1. I know that's behind the curve, but
> sometimes don't these packages include bugfixes from newer versions
> than they report?
> I can begrudgingly compile from source, but would not be happy taking
> it outside the system package manager.
> I just tried to test by putting the host in the config file, got this
> startup error:
> DHCP4_PARSER_FAIL failed to create or run parser for configuration
> element subnet4: unsupported configuration parameter 'client-classes'
I think you meant client-classes failed to parse as part of the host
element (not subnet4) ?  But yes, "client-classes" was added in 1.1.0.
1.1.0 added a good deal more functionality to the RDBMS Host
Reservations implementations, as well as a lot more with classification
expression matching.
> Looks like assigning client-classes to host reservations was a feature
> only added after version 1.0? Can you please confirm when it was added?
> _______________________________________________
> Kea-users mailing list
> Kea-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/kea-users

When an inbound packet is received things happen in this order:

1. The packet is classified by evaluating it against the test expression
for defined classes

2. Subnet matching is conducted based on packet content.  This includes
comparing the classes matched to the packet in step 1 against the
classes specified by the subnet's "client-class" list.

3. Look for host reservations

The problem you have is two fold.   First, your "test-class" does not
define a "test" expression and thus matching it against a packet always
fails.   This causes the subnet selection to fail and the server drops
the packet.  The second issue is that you are assigning a class to the
host reservation, but associating the client to a reservation occurs
after the subnet selection.  This is something of a chicken-and-the-egg

So while you can specify that a host belongs to one or more classes,
this currently only means the host inherits options from those classes. 

I think it would help to understand what problem you are trying to
solve.  Are you trying to ensure that only known clients get addresses? 
Are you trying to map specific hosts to specific subnets?   How any
hosts in how many subnets do you anticipate having?

If your network isn't large, you could define a class for each host
whose "test" expression matches the host's hardware address. Then add
these classes to the desired subnet4 client-class list.   Not ideal but
it would work.  This would be akin to ISC DHCP sub-classing,  though not
quite as neat.   Another alternative would be to write a hook but we
would need to understand your problem to offer a more detailed
suggestion.  Our example hook library, user-chk,  does something similar
to what you're after and is a good starting point for what is possible,
http://kea.isc.org/docs/kea-guide.html#idp54000992.   Hooks are
described in detail in our developer's guide:

Thomas Markwalder

ISC Software Engineering

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