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

[Chaigneau, Nicolas]

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).
Hence, two leases will be offered at the same time.

This doesn't seem right.


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 ?


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?

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)
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 ?



Thanks for your time.

Regards,
Nicolas.


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