A DHCP client broadcasts DHCP Discover messages and all devices on the network segment will receive these messages. When multiple DHCP servers or DHCP relay agents are deployed on a network segment, the client accepts only the first DHCP Offer message it receives and therefore may obtain an unexpected IP address. Planning DHCP servers helps you ensure that clients on your network obtain network parameters from an expected DHCP server.
When planning servers, note the following:
Plan VLANs to ensure that only one DHCP server (or a DHCP relay agent) can receive DHCP Discovery messages in a VLAN.
Configure DHCP snooping on client access devices to ensure that the clients apply to the correct DHCP servers for network parameters. For details about configuring DHCP snooping, see DHCP Snooping Configuration in the S2720, S5700, and S6700 V200R019C10 Configuration Guide - Security.
Plan the range of IP addresses that can be allocated and the mechanisms (such as dynamic or static) used to allocate the IP addresses.
Plan the IP addresses that cannot be allocated from an address pool. For example, in an enterprise, a DHCP server allocates IP addresses on the network segment 192.168.1.0/24 to employee PCs. On this network segment, 192.168.1.10 has been used by a DNS server and must be excluded from the address pool to prevent IP address conflicts.
Plan an IP address lease for a DHCP client based on the expected time that the client will be online. By default, the IP address lease is 1 day.
In scenarios where clients often move and stay online for a short period of time, for example, in cafes, airports, and hotels, plan a short-term lease to ensure that IP addresses are released quickly after the clients go offline.
In scenarios where clients seldom move and stay online for a long period of time, for example, in office areas of an enterprise, plan a long-term lease to prevent services from being affected by frequent lease or address renewals.
If a DHCP client needs to communicate with other network devices through a domain name and obtain DNS parameters using DHCP, plan the IP address of the DNS server and domain name of the client.