In Administering Windows Server Hybrid Core Infrastructure, Microsoft states that high availability for DHCP on Windows Server is achieved by using DHCP failover rather than the legacy split-scope (80/20) model. The guidance explains that DHCP failover “synchronizes lease data between two DHCP servers and can be configured in Load Balance or Hot Standby mode on a per-scope basis,” and that you enable it on each DHCP scope to create a partner relationship that automatically replicates scope configuration and active leases. This meets the requirement to keep address assignment available if one DHCP server is down.
The same materials further note that DHCP broadcasts do not traverse routers; therefore, when the partner server is reachable across a routed boundary (another site/subnet), you must configure the router as a DHCP relay (IP helper) to forward DHCPDISCOVER messages to the remote DHCP server(s). The text emphasizes: “When clients and DHCP servers are on different subnets, configure a relay agent on the router to forward requests to the DHCP server IP addresses.”
Applying this to Fabrikam: create DHCP failover between DHCP1 (Scope1) and DHCP2 (Scope2) (E) and configure the routers in New York and Seattle as DHCP relays that forward to both DHCP servers (B). You do not use Failover Clustering for DHCP here, and you do not create extra 25% scopes; those are split-scope practices superseded by DHCP failover.
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