Can somebdy give an advice how to pass over the following feature?
A routing switch with "ip snooping enabled" drops DHCP packets if their source IP is not equal 0.0.0.0 [see page 22-3 C3750 Switch Software Configuration Guide 12.2(25)SEE]. It means that a host using DHCP Relay (ip helper-address) can not confirm its IP address at DHCP server earlier than its IP address expires. Than in seconds obtain a new one but
it is enough to break network applications. That way it is unusable.