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Story
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Resolution: Done
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Undefined
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None
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None
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None
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None
-
rhel-stacks-services-scripting
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ssg_core_services
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None
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False
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False
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-
None
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None
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None
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None
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None
UPDATE 04/09/25:
Since 2.7.7 the ping check hook has been open sourced, release notes:
210. [func] razvan The following hook libraries are now open source: for the kea-dhcp4 and the kea-dhcp6 servers 'libdhcp_class_cmds', 'libdhcp_ddns_tuning', 'libdhcp_flex_id', 'libdhcp_legal_log', 'libdhcp_host_cache', 'libdhcp_host_cmds', 'libdhcp_lease_query', 'libdhcp_limits', 'libdhcp_ping_check', 'libdhcp_radius', 'libdhcp_subnet_cmds' and for the kea-dhcp-ddns server 'libddns_gss_tsig'. (Gitlab #3333)
This is an actively used ISC DHCPD functionality by our customers to check whether IP address is already taken before offering it to the client.
DHCPD config snippet:
ping-check true;
ping-timeout 2;
It's not supported by Kea, it will be in 2.6 stable, but only as a commercial hook:
https://kb.isc.org/docs/why-doesnt-kea-support-ping-check
It is advised to use dhcp client that scans the network by itself and supports DECLINE msg to inform Kea not to offer this IP for `decline-probation-period` interval. DHCPCD supports this.
It would be good o create KB about this.
Update:
Ping check got recently implemented/supported in commercial version since 2.6.0, from Release Notes:
2. **Ping Check hook**: One of the few ISC DHCP features that was not
previously available in Kea is ping check; following customer requests,
it has now been added. The basic idea is that, before handing out an
IPv4 lease, the Kea DHCP server attempts to ping the address to be
offered. If it receives a response, it marks the lease as being declined
and discards the offer. Pings are not 100% reliable due to access
technologies, firewalls, broken clients, and other factors, but in some
deployments ping check may be very helpful [#3008, #3008, #3012, #3053,
#3054, #3055, #3083, #3187, #3110]. A new hook point `lease4-offer` was
implemented [#3063, #3038] and documented [#3067]. This hook was tested
on Linux and BSD systems [#3101, #3099]. The Ping Check hook library is
available only to ISC paid support subscribers. [#2781, #3084, #3165].