DHCPD not sending NACK to client

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Joined: 2019/05/10 18:48:35

DHCPD not sending NACK to client

Post by lcroce » 2019/09/23 14:46:52

First off, I apologize if this is the wrong forum to post this. I've been configuring DHCPD for IPv6 and I'm running into an issue where clients are not getting a NACK from the server if they previously had an address in a different subnet. So for example, I have a client on 2620:56:6000:406::/64 that was previously on 2620:56:6000:417::/64 and had a valid IP for that network. The server isn't sending a NACK saying that the addresss is an invalid IP for the current network and so the client assumes that it can use the address.

From my understanding the authoritative flag is what is supposed to perform this function but it doesn't appear to be doing that from wireshark captures I've taken. The client in question is running MacOS. Both Windows and Linux clients appear to ignore the missing NACK and request a new address anyway. I'm including the relevant portions of my DHCP config below. I've tried asking about this on the ISC DHCP-Users mailing list but got no response.

Code: Select all

default-lease-time 2592000;
preferred-lifetime 604800;
option dhcp-renewal-time 3600;
option dhcp-rebinding-time 7200;
allow leasequery;

option dhcp6.name-servers 2620:56:6000:516::16:1, 2620:56:6000:1516::16:1, 2620:56:6000:516::16:2, 2620:56:6000:1516::16:2;
option dhcp6.sntp-servers 2620:56:6000:516::16:1, 2620:56:6000:1516::16:1, 2620:56:6000:516::16:2, 2620:56:6000:1516::16:2;
option dhcp6.domain-search "bju.edu";

option dhcp6.preference 255;
option dhcp6.info-refresh-time 21600;

dhcpv6-lease-file-name "/var/lib/dhcpd/dhcpd6.leases";

subnet6 2620:56:6000:406::/64 {
        range6 2620:56:6000:406:8000:: 2620:56:6000:406:bfff:ffff:ffff:ffff;
        #range6 2620:56:6000:406:c000:: 2620:56:6000:406:ffff:ffff:ffff:ffff;

subnet6 2620:56:6000:417::/64 {
        range6 2620:56:6000:417:8000:: 2620:56:6000:417:bfff:ffff:ffff:ffff;
        #range6 2620:56:6000:417:c000:: 2620:56:6000:417:ffff:ffff:ffff:ffff;

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