Hello,
I found a use case in which KEA DHCP server behaves differently than I
expected and I would like to ask if it was meant to behave that way or
there is a problem in my configuration. Here is the description:
Imagine you have a known host client-X with a reserved IP address
10.0.0.9. client-X usually connects via the Shared-B network, but one
day it wants to connect via Shared-A. The IP address reserved for
client-X does not match any of the subnets in Shared-A. Therefore, I
would expect that it would be given an IP address from the pool in the
subnet 10.1.1.0/24 (that is how it works in ISC DHCP). However, it is
given it's reserved IP 10.0.0.9 along with the options from the subnet
10.1.1.0/24, which does not make sense to me. Is this how it was meant
to behave?
I found a solution how to make the client-X get an IP address from the
pool in the subnet 10.1.1.0/24 by moving the host reservation from the
global scope to the scope of the subnet 10.0.0.0/24. Anyway, I've been
wondering why it doesn't work the same way with the global reservations.
I tried the global mode first, as I am using host reservations in groups
(which are global) in ISC DHCP and it works as expected there.
Could you please give it a look? Thanks in advance. See the
corresponding configuration and the demonstration of the use case below.
Best regards,
Maria Hrabosova
---
kea-dhcp4.conf:
{
"Dhcp4": {
"interfaces-config": {
"interfaces": [
"server-eth0"
],
"dhcp-socket-type": "udp"
},
"control-socket": {
"socket-type": "unix",
"socket-name": "/tmp/kea-dhcp4-ctrl.sock"
},
"lease-database": {
"type": "memfile"
},
"shared-networks": [
{
"name": "Shared-A",
"relay": {
"ip-address": "192.0.2.1"
},
"subnet4": [
{
"subnet": "10.1.1.0/24",
"pools": [
{
"pool": "10.1.1.200 - 10.1.1.250"
}
],
"option-data": [
{
"name": "routers",
"data": "10.1.1.1"
},
{
"name": "domain-name-servers",
"data": "10.1.1.2, 10.1.1.3"
}
]
}
]
},
{
"name": "Shared-B",
"relay": {
"ip-address": "192.0.1.1"
},
"subnet4": [
{
"subnet": "10.0.0.0/24",
"pools": [
{
"pool": "10.0.0.200 - 10.0.0.250"
}
],
"option-data": [
{
"name": "routers",
"data": "10.0.0.1"
},
{
"name": "domain-name-servers",
"data": "10.0.0.2, 10.0.0.3"
}
]
}
]
}
],
"host-reservation-identifiers": [
"hw-address"
],
"reservation-mode": "global",
"reservations": [
{
"hw-address": "aa:a0:00:00:11:10",
"ip-address": "10.0.0.9",
"hostname": "client-X"
}
]
}
}
---
dhclient-debug.sh:
#!/bin/sh
env
---
ip add
...
link/ether aa:a0:00:00:11:10 brd ff:ff:ff:ff:ff:ff link-netnsid 1
...
dhclient client1-eth0 --timeout 2 -sf dhclient-debug.sh -H client-X
...
new_ip_address=10.0.0.9
new_routers=10.1.1.1
new_domain_name_servers=10.1.1.2 10.1.1.3
...
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