The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) local area networks. A DHCP server must be present on the network. A device connected to the network requests an IP address from the DHCP server using the DHCP protocol; the server assigns a unique address to the device, A device configured to use dynamic (DHCP) addressing that is connected to a different network will be assigned an address on that network without needing to be reconfigured.
DHCP operates based on the client–server model. When a computer or other device connects to a network, the DHCP client software sends a DHCP broadcast query requesting the necessary information. Any DHCP server on the network may service the request. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as default gateway, domain name, the name servers, and time servers. On receiving a DHCP request, the DHCP server may respond with specific information for each client, as previously configured by an administrator, or with a specific address and any other information valid for the entire network and for the time period for which the allocation (lease) is valid. A DHCP client typically queries for this information immediately after booting, and periodically thereafter before the expiration of the information. When a DHCP client refreshes an assignment, it initially requests the same parameter values, but the DHCP server may assign a new address based on the assignment policies set by administrators.
On large networks that consist of multiple links, a single DHCP server may service the entire network when aided by DHCP relay agents located on the interconnecting routers. Such agents relay messages between DHCP clients and DHCP servers located on different subnets. [1]
The imRAD provides both the DHCPv4 and DHCPv6 service.
DHCPv4
DHCPv4 환경에서 클라이언트는 브로드캐스트(Broadcast) 방식으로 사용할 IPv4 주소를 요청합니다.
따라서 DHCP 서버가 클라이언트와 같은 VLAN에 포함되어 있지 않다면 이러한 요청이 서버에 전달 될 수 없으므로 L3 스위치 혹은 라우터의 bootprelay(또는 dhcp Helper)설정을 통해 DHCP 브로드캐스트를 DHCP 서버까지 전달해야 합니다.
서버는 이러한 Helper를 통해 클라이언트가 어느 VLAN에 속한지를 판단합니다.
DHCPv6
DHCPv6는 DHCPv4와 달리 모든 요청이 멀티캐스트(Multicast) 방식으로 이뤄집니다.
멀티캐스트 또한 VLAN을 벗어나 요청이 전달 될 수 없으므로 DHCP 서버와 다른 VLAN에 포함된 클라이언트에 IPv6 주소를 할당하려면 L3 스위치 혹은 라우터의 bootprelay(또는 dhcp Helper)설정이 필요합니다.
추가적으로 DHCPv6 환경에서는 Router solicitation과 router advertisement 기능이 반드시 설정되어야 할당된 IPv6 주소를 이용해 네트워크를 사용 할 수 있습니다.
자세한 통신 흐름은 DHCPv6 communication을 참고하세요.