[Kea-users] kea dhcp4 - configuration of local listening IP addr ?

[Marcin Siodelski]

FYI, I submitted a ticket: http://kea.isc.org/ticket/3539 for this request.

Marcin

On 04/09/14 13:19, Marcin Siodelski wrote:
> Nicolas,
> 
> Thanks again for spending your time on testing Kea. Please see my
> answers inline.
> 
> Marcin
> 
> On 04/09/14 11:45, Chaigneau, Nicolas wrote:
>>  
>>
>> Additionally, if an interface has 2 IP addresses:
>>
>>  
>>
>> When kea receives a message on the interface (whatever the IP address
>> used), it will handle it twice (one for each IP address).
> 
> Yes, this use case requires additional configuration parameter to
> specify what address on the interface the server should listen.
> Currently, Kea configuration doesn't provide this parameter and it
> creates sockets for all addresses regardless if this is the same or
> different interface. I will submit a ticket for this feature.
> 
>>
>> Hence, two leases will be offered at the same time.
>>
>>  
>>
>> This doesn’t seem right.
>>
>>
> 
> Agreed.
> 
>>
>>  
>>
>> *De :*kea-users-bounces at lists.isc.org
>> [mailto:kea-users-bounces at lists.isc.org] *De la part de* Chaigneau, Nicolas
>> *Envoyé :* jeudi 4 septembre 2014 11:36
>> *À :* kea-users at lists.isc.org
>> *Objet :* [Kea-users] kea dhcp4 - configuration of local listening IP addr ?
>>
>>  
>>
>> Hello,
>>
>>  
>>
>>  
>>
>> I have a question about kea-dhcp4 configuration related to server local
>> address.
>>
>>  
>>
>>  
>>
>> Kea administration guide explains that you can specify a list of
>> interfaces on which the server will listen, such as:
>>
>> "interfaces": [ "eth0", "eth1" ],
>>
>>  
>>
>> Is it possible to restrict this to a single IP address for a given
>> interface ?
>>
>>  
> 
> As I stated above: it is not possible. For DHCPv6 we use the following
> notation to bind sockets to global unicast addresses (in addition to the
> sockets bound to All_DHCP_Servers_and_Relay_Agents multicast address):
> 
> "interfaces": [ "eth0/2001:db8:1::1", "eth1/3001::1" ]
> 
> I think we could use similar notation to restrict the DHCPv4 server to
> listen on selected IPv4 addresses:
> 
> "interfaces": [ "eth0/10.1.2.3" ]
> 
>>
>>  
>>
>> With ISC’s dhcpd, this was achieved with the configuration item
>> “local-address”.
>>
>> This allowed to start multiple servers on the same host, using the same
>> interface, but each having its own local IP address.
>>
>>  
>>
>> I did not find a similar option with kea ; did I miss something ?
>>
>>  
>>
>>  
>>
>> I tested the following scenario:
>>
>> - Start a dhcpd, which listens on a given interface, and binds to a
>> specific local IP addr
>>
>> - Start kea-dhcp4, with the same interface as used by dhcpd
>>
>> Kea starts, but compains that it cannot bind to the IP addr used by dhcpd:
>>
>> 2014-09-04 11:15:23.386 WARN  [kea-dhcp4.dhcp4/7595]
>> DHCP4_OPEN_SOCKET_FAIL failed to open socket: failed to open socket on
>> interface eth0.102, reason: failed to bind fallback socket to address
>> 10.163.216.229, port 67, reason: Address already in use - is another
>> DHCP server running?
>>
> 
> Kea is not meant to bind to addresses in use. So, if there is another
> DHCP server running and listening on the particular interface (and
> address), Kea should complain and not open a socket. I think that was
> also an intent for dhcpd.
> 
>>  
>>
>> Then, if a DHCP message is sent by a relay to dhcpd local IP addr, two
>> responses are sent back: both dhcpd and kea manage to answer! (even
>> though kea couldn’t bind to this IP address, apparently the interface is
>> enough)
> 
> Hm, is there any other interface that Kea is listening on and can
> receive relayed messages?
> 
> Would it be possible to get the traffic capture that shows this behavior?
> 
>>
>> This is weird.
>>
>>  
>>
>>  
>>
>> On the opposite, if I start first kea, then dhcpd, dhcpd fails to start
>> because it cannot bind on the local address:
>>
>> Can't bind to dhcp address: Address already in use
>>
>>  
>>
>>  
>>
>>  
>>
>> Is this the intended behavior ?
>>
>>  
> 
> 
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