DHCP relay agents listen for the DHCP messages that are broadcast on the local subnet and route them to a DHCP server on a different subnet. Because broadcast packets do not typically traverse routers, without a DHCP relay agent you would need to install a DHCP server on every network subnet on which DHCP clients reside. DHCP relay allows you to consolidate your DHCP servers into the much smaller number that you need for load balancing and fault tolerance.
For more information, see Configure the IPv4 DHCP Relay Agent.
Additional references
- IPv4
RRAS and DHCP (https://go.microsoft.com/fwlink/?linkid=140605)