[Kea-users] Duplicate Addresses, address pool exhaustion with DHCPDECLINE flood

Mohammed Khallaf mohammed.khallaf at nagwa.com
Thu Apr 18 07:08:09 UTC 2019


Hello Kari,

I'm not sure about Kea, Kea hooks, or if someone is going to write a Kea
hook for that, but there is no DHCP server that I know about that
implements this outside-of-the-box. Actually, most or all effective
solutions in network-originating layer 2 attacks are basically built on
networking devices software and/or network monitoring software, or the
least: manual troubleshooting.

If your switching equipment has a feature to help, then use it. If not, you
can set a network monitoring software that analyzes DHCP DISCOVER messages
and alert you if the rate from a specific MAC is abnormal, or the general
rate on the network is abnormal. SolarWinds and PRTG come to mind.

--
MK


On Wed, Apr 17, 2019 at 2:56 PM Kari Karvonen <kari.karvonen at kasenet.fi>
wrote:

> Hello
>
> If there is faulty DHCP-client on a network that keeps requesting IP's
> and after receiveing IP-offer client sends DHCPDECLINE and DHCP-server
> marks IP-address as declined for 24 hours. If client keeps repeating
> this, address after address will be marked as declined and soon entire
> DHCP-pool is exhausted.
>
> I looked Kea 1.5.0 user guide and found that it is possible to shorted
> decline time
>
>   "decline-probation-period": 3600
>
> But is there something else on dhcp-server side to prevent this kind of
> behaviour?
>
> --
> Kari Karvonen
> Network specialist
> +358445557360
> www.kasenet.fi
> _______________________________________________
> Kea-users mailing list
> Kea-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/kea-users
>
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