KEA not respecting reservation

[Christophe999s]

KEA hands out a different IP than the one configured in the reservations:



This happened after replacing the sdcard in my pi en restarting it.
Anyone experience something similar or know what the cause might be?

[MarkH]

The KEA error log explains the address you chose for hifiberryamp is not available, as it's already in use, so instead it's advertised (offered) 192.168.30.101.

Static lease changes from ISC DHCP to KEA:

DHCP reservations must fall within the Interface subnet and must be outside any DHCP scope defined in KEA DHCP server.

This is a more strict configuration requirement than the legacy ISC DHCP Server.

Having static leases defined that fall within a scope does not prevent a DHCP server from offering that IP as a lease, which may (mistakenly) be the expected behaviour.

In your question you don't specify what your DHCP scope(s) [also known as pool(s)] is/are, so I'll assume you've left these as default which matches the interface's subnet.

This is an example of a CORRECT config:

Code: [Select]

Interface subnet: 192.168.30.0/24
Interface Useable IPs: 192.168.30.1 - 192.168.30.254
Interface IP: 192.168.30.1/24
DHCP Scope: 192.168.30.1 - 192.168.30.180
DHCP static lease for mac address: d8:3a:dd:fc:44:82 192.168.30.182

And below is an example of a INCORRECT config:

Code: [Select]

Interface subnet: 192.168.30.0/24
Interface Useable IPs: 192.168.30.1 - 192.168.30.254
Interface IP: 192.168.30.1/24
DHCP Scope: 192.168.30.1 - 192.168.30.254
DHCP static lease for mac address: d8:3a:dd:fc:44:82 192.168.30.182

If this doesn't work, can you confirm the scope(s) set for KEA on this interface

[charles.adams]

I'd say that it is odd to me that what is a permanent lock between MAC address and IP in every other system I've used (Microsoft, Cisco, Ubiquity), that over rules the scope and locks the IP down to a particular device, is accomplished by having to manually carve out the IPs from the DHCP scope instead of just locking the IPs down to their assignment and keeping it simpler for the person doing the configuration.

[hansen97124]

just wanted to say thanks.  This post solved the problem I was having with ignored reservations.

All working now after following this thread.

[themadwizard]

And here I thought only Sophos firewalls were stupid enough to require you to break up pools to reserve addresses in the pool space.  Awful design.

The KEA error log explains the address you chose for hifiberryamp is not available, as it's already in use, so instead it's advertised (offered) 192.168.30.101.

Static lease changes from ISC DHCP to KEA:

DHCP reservations must fall within the Interface subnet and must be outside any DHCP scope defined in KEA DHCP server.

This is a more strict configuration requirement than the legacy ISC DHCP Server.

Having static leases defined that fall within a scope does not prevent a DHCP server from offering that IP as a lease, which may (mistakenly) be the expected behaviour.

In your question you don't specify what your DHCP scope(s) [also known as pool(s)] is/are, so I'll assume you've left these as default which matches the interface's subnet.

This is an example of a CORRECT config:

Code: [Select]

Interface subnet: 192.168.30.0/24
Interface Useable IPs: 192.168.30.1 - 192.168.30.254
Interface IP: 192.168.30.1/24
DHCP Scope: 192.168.30.1 - 192.168.30.180
DHCP static lease for mac address: d8:3a:dd:fc:44:82 192.168.30.182

And below is an example of a INCORRECT config:

Code: [Select]

Interface subnet: 192.168.30.0/24
Interface Useable IPs: 192.168.30.1 - 192.168.30.254
Interface IP: 192.168.30.1/24
DHCP Scope: 192.168.30.1 - 192.168.30.254
DHCP static lease for mac address: d8:3a:dd:fc:44:82 192.168.30.182

If this doesn't work, can you confirm the scope(s) set for KEA on this interface

[dseven]

Kea DHCP *does* support in-pool reservations: https://kea.readthedocs.io/en/kea-2.6.1/arm/dhcp4-srv.html#address-reservation-types

but there are caveats - mostly around cases where an address from the pool had already been given out as a dynamic lease to some other host before a reservation for it was created.

OPNsense recommends not using in-pool reservations https://docs.opnsense.org/manual/dhcp.html#reservations but does allow it. I'm not sure the statement made there ("the DHCP server is free to offer this IP address to a different client when the first client goes offline") is accurate - that's not how I read the Kea docs, but I haven't actually tested it...