[Kea-users] KEA not send a NAK when request ip is out of scope

Thomas Andersen than at itu.dk
Thu Aug 29 12:29:59 UTC 2019

Hi again,

Sorry for bumping, but I’m sure there must be smart people out there who can guide me – you just missed my original email. :)

But to make it a lot more simple:
Shouldn’t KEA respond with NAK when client is requesting an IP out of configured scope?


From: Kea-users <kea-users-bounces at lists.isc.org> on behalf of Thomas Andersen <than at itu.dk>
Date: Thursday, 22 August 2019 at 10.19
To: "kea-users at lists.isc.org" <kea-users at lists.isc.org>
Subject: [Kea-users] KEA not send a NAK when request ip is out of scope


I got some problems with DHCP requests.

Expected scenario:
Computer logs on wifi with host login and is assigned to vlan 200 (
User logs into computer an reauthenticate on wifi and is assigned to vlan 201 (
Windows 10 sends a DHCP request for the ip address on vlan 200.
KEA sends a NAK, as the requested ip is not in scope.
Windows sends DHCP discover and so forth.

What we see is that KEA never sends the NAK, but sees the REQUEST packet as a bad packet, and then discards it.
How can I get KEA to send a NAK?
I’ve tried this with 1.3 and 1.5

2019-08-21 13:40:24.683 DEBUG [kea-dhcp4.packets/41217] DHCP4_PACKET_RECEIVED [hwtype=1 a0:51:0b:0c:24:93], cid=[01:a0:51:0b:0c:24:93], tid=0xef9810de: DHCPREQUEST (type 3) received from to on interface eth0
2019-08-21 13:40:24.683 DEBUG [kea-dhcp4.packets/41217] DHCP4_QUERY_DATA [hwtype=1 a0:51:0b:0c:24:93], cid=[01:a0:51:0b:0c:24:93], tid=0xef9810de, packet details: local_address=, remote_address=, msg_type=DHCPREQUEST (3), transid=0xef9810de,
  type=012, len=008: "PC622019" (string)
  type=050, len=004: (ipv4-address)
  type=053, len=001: 3 (uint8)
  type=055, len=014: 1(uint8) 3(uint8) 6(uint8) 15(uint8) 31(uint8) 33(uint8) 43(uint8) 44(uint8) 46(uint8) 47(uint8) 119(uint8) 121(uint8) 249(uint8) 252(uint8)
  type=060, len=008: "MSFT 5.0" (string)
  type=061, len=007: 01:a0:51:0b:0c:24:93
  type=81 (CLIENT_FQDN), flags: (N=0, E=0, O=0, S=0), domain-name='pc622019.itu.local' (partial)
2019-08-21 13:40:24.684 DEBUG [kea-dhcp4.bad-packets/41217] DHCP4_NO_LEASE_INIT_REBOOT [hwtype=1 a0:51:0b:0c:24:93], cid=[01:a0:51:0b:0c:24:93], tid=0xef9810de: no lease for address requested by INIT-REBOOT client

Med venlig hilsen / With best regards
Thomas Andersen

Network Architect

IT University of Copenhagen
Rued Langgaards Vej 7
2300 København S

Phone: +45 72185249



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