Why does the DHCP client resend DHCPDISCOVER if it has already received an address up to a few seconds before?

Question

Domain Name System

Actually, I recently installed a new gateway on FreeBSD 10.3 with isc-dhcp43 and bind910. DDNS configured. Everything is OK, except that every morning in messages I see something like this:
Apr 15 08:10:10 mail dhcpd: Forward map from comp1.localdomain.ru to 192.168.1.245 FAILED: Has an address record but no DHCID, not mine.
And here is the dhcpd.log:
Apr 15 08:09:43 mail dhcpd: DHCPDISCOVER from 50:46:5d:8c:77:20 via rl0
Apr 15 08:09:44 mail dhcpd: DHCPOFFER on 192.168.1.187 to 50: 46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:09:55 mail dhcpd: DHCPDISCOVER from 50:46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:09:55 mail dhcpd: DHCPOFFER on 192.168.1.187 to 50:46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:09:55 mail dhcpd: DHCPREQUEST for 192.168.1.187 (192.168.10.5) from 50:46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:09:55 mail dhcpd: DHCPACK on 192.168 .1.187 to 50:46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:10:08 mail dhcpd: DHCPACK to 192.168.1.187 (50:46:5d:8c:77:20) via rl0
Apr 15 08:10:09 mail dhcpd: DHCPDISCOVER from 50:46:5d:8c:77:20 via rl0
Apr 15 08:10:10 mail dhcpd: DHCPOFFER on 192.168.1.245 to 50:46:5d:8c:77: 20 (comp1) via rl0
Apr 15 08:10:10 mail dhcpd: DHCPREQUEST for 192.168.1.245 (192.168.10.5) from 50:46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:10:10 mail dhcpd: DHCPACK on 192.168.1.245 to 50:46:5d:8c:77:20 (comp1) via rl0
And similar messages in the logs come from two more specific computers on the network. The rest don't complain. Why comp1 first sends 2 DHCPDISCOVER, and then, having already received the address after all, sends a request again. As a result, 3 DHCPDISCOVER's, while the latter is ignored by comp1 itself and it remains with the first received address, i.e. 192.168.1.187
It is logical that DHCP will swear "192.168.1.245 FAILED: Has an address record but no DHCID, not mine" because for comp1 there is already an entry for 192.168.1.187 in the dns
Can anyone come across this?

Answer 1

You need to look at the contents of the packets, otherwise it's hard to understand what's going on, try sniffing the traffic. DHCP Discover can be not only for obtaining an IP address, some services, such as WPAD, also use DHCP, with a separate request.
It seems more strange to me that you are
getting Apr 15 08:09:55 mail dhcpd: DHCPACK on 192.168.1.187 to 50:46:5d:8c:77:20 (comp1) via rl0
Apr 15 08:10:08 mail dhcpd: DHCPACK to 192.168.1.187 (50:46:5d:8c:77:20) via rl0
two ACKs per DHCPREQUEST. And do you happen to have a DHCP gateway raised somewhere? Maybe the server is waiting for a response from the gateway, because the gateway always responds with a delay, and the response to the address request when updating the release usually takes precedence over the broadcast.