Some ISPs temporarily block clients that send too many DHCP requests. Here is an example from this forum: http://forum.mikrotik.com/t/dhcp-client-retry-interval/66370/1
RFC 2131 contains:
DHCP clients are responsible for all message retransmission. The
client > MUST > adopt a retransmission strategy that incorporates a
randomized > exponential > backoff algorithm > to determine the delay
between retransmissions. The delay between retransmissions SHOULD be
chosen to allow sufficient time for replies from the server to be
delivered based on the characteristics of the internetwork between
the client and the server. For example, in a 10Mb/sec Ethernet
internetwork, the delay before the first retransmission SHOULD be 4
seconds randomized by the value of a uniform random number chosen
from the range -1 to +1.
However, dhcp-client on RouterOS 6.49.5 does not exponentially increase the delay (timeout) when it retransmits DHCP messages. Delay can be as small as 1 second.
Please, check the screenshot. Wireshark dump can be downloaded here: https://disk.yandex.ru/d/urZmF8Spz3Z_VA.
