Configuring DHCP
DHCP configuration includes configuration of a DHCP server, configuration of DHCP clients, and optional configuration of DHCP relay agents and BOOTP clients. Server configuration enables the server to send network parameters to the client, client configuration determines how clients request network parameters, and relay agent configuration enables a relay agent to forward DHCP messages between clients and servers that are on different physical subnets.
- Planning Data
- Default Settings for DHCP
- Configuring a DHCP Server
- Enabling DHCP
- Enabling the DHCP Server Function
- (Optional) Configuring DHCP Data Restoration
- (Optional) Configuring IP Address Conflict Detection
- (Optional) Configuring a DHCP Server to Dynamically Allocate IP Addresses to BOOTP Clients
- (Optional) Forcing a DHCP Server to Reply with a DHCP NAK Message
- Creating an Address Pool
- (Optional) Configuring the Range of IP Addresses in an Address Pool
- (Optional) Excluding IP Addresses from an Address Pool
- (Optional) Configuring Fixed IP Addresses in an Address Pool
- (Optional) Configuring an Address Lease Time
- (Optional) Configuring Automatic Reclaim of Conflicting IP Addresses in an Address Pool
- (Optional) Configuring the Alarm Function for IP Address Exhaustion
- (Optional) Configuring the Logging Function for IP Address Allocation
- (Optional) Configuring a Gateway Address for Clients
- (Optional) Configuring a Configuration File for a DHCP Client
- (Optional) Configuring User-defined Options
- (Optional) Configuring DNS Configurations Allocated by a DHCP Server
- (Optional) Configuring NetBIOS Configurations Allocated by a DHCP Server
- (Optional) Configuring a SIP Server Address to Be Allocated by the DHCP Server
- Verifying the DHCP Server Configuration
- Enabling DHCP
- Enabling the DHCP Relay Function
- Specifying the DHCP Server IP Address
- (Optional) Configuring Strategies for Processing Option 82 Information on a DHCP Relay Agent
- (Optional) Configuring User Entry Detection on a DHCP Relay Agent
- (Optional) Configuring the Processing Methods of DHCP ACK and DHCP Request Messages
- Verifying the DHCP Relay Agent Configuration
- Enabling the DHCP Client Function
- (Optional) Configuring Attributes
- (Optional) Configuring an Expected Lease
- (Optional) Configuring Gateway Detection
- (Optional) Configuring Option Information Requested by a DHCP Client
- Verifying the DHCP Client Configuration
- Enabling the BOOTP Client Function
- (Optional) Configuring Attributes
- (Optional) Configuring Gateway Detection
- Verifying the DHCP Client Configuration
- Viewing Statistics About DHCP Messages
- Clearing Statistics About DHCP Messages
- Resetting a DHCP Address Pool
- Locking a DHCP Address Pool
- Forcing a DHCP Client to Release and Renew Its IP Address
- Withdrawing the Fixed IP Addresses Assigned to Clients
Planning Data
Planning DHCP Servers
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.
Planning IP Addresses
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.
Planning Leases
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.
Planning DNS Parameters
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.