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I previously had a C3200 and replaced with a C4000. On both units, when I reserve multiple IPs outside of the DHCP pool range for my LAN, DHCP stops working. All DHCP clients can no longer get an IP from the pool. When I disable the address reservations, the DHCP Client List once again floods with clients that have been unable to get an IP. All the sudden, they work again. This is the strangest thing. Toggling the DHCP server and power cycling the router have no effect. The only way to restore DHCP server function is to disable the address reservations for all but 1 client.

IP Pool: 192.168.101 - 192.168.1.199
Gateway: 192.168.1.1

Address Reservations for 192.168.1.2, 192.168.1.3, 192.168.1.5 and 192.168.1.50.
Static IPs are assigned to an iMac, MacBook Pro, a home built FreeBSD server and an IP Camera.
All other clients (27 of them) are assigned via DHCP, ranging from Chromecasts, to echo devices, iPads, kindles, etc..

Knowledge background: I've worked over 10 years at a major telco provider on Layer 2 / Layer 3 access network management (DSLAM/VDSL/PON) and have extensive knowledge of IP.