Some site USG5100 BSR（V1R3）failure, it need to replace, the spare part version is V1R5，add one item in original configuration：dhcp server detect ，but there is not this command on V1R5 version.
Open dhcp snooping enable for global
Open dhcp snooping enable on interface
The interface connecting dhcp server configured as dhcp snooping trust
dhcp snooping trusted
Dhcp server detect command in V1R3 is used for identify "false DHCP server", the function in V1R5 consolidate to dhcp snooping function.
（1）V1R5 version configuration command is different from the former version.
（2）DHCP Snooping is one kind of DHCP safe feature, by MAC address limit，DHCP Snooping safe bonding, IP + MAC bonding, Option82 feature function can fiitrate the DHCP information untrust，it solves the problem that DHCP Server false attack, arp middleman attack, IP/MAC Spoofing attack and DHCP DoS attack when the device apply, the function of DHCP Snooping is that establish one firewall between client and dhcp server.