Configuration considerations for DHCP servers
The following configuration considerations apply to DHCP servers, the DHCP binding database, and DHCP address pools.
- The DHCP server is supported in the Layer 2 and Layer 3 software images.
- DHCP server is not supported on non-default VRF.
- In the event of a controlled or forced switchover, a DHCP client requests from the DHCP server the same IP address and lease assignment that it had before the switchover. After the switchover, the DHCP server will be automatically re-initialized on the new Active Controller or management module.
- For DHCP client hitless support in a stack, the stack mac command must be used to configure the MAC address, so that the MAC address does not change in the event of a switchover or failover. If stack mac is not configured, the MAC address/IP address pair assigned to a DHCP client will not match after a switchover or failover. Furthermore, in the Layer 3 router image, if the stack mac configuration is changed or removed and the management port has a dynamic IP address, when a DHCP client tries to renew its lease from the DHCP server, the DHCP server will assign a different IP address.
- If any address from the configured DHCP pool is used, for example, by the DHCP server or TFTP server, you must exclude the address from the network pool.
- Ensure that DHCP clients do not send DHCP request packets with a Maximum Transmission Unit (MTU) larger than 1500 bytes. Brocade devices do not support DHCP packets with an MTU larger than 1500 bytes.
DHCP binding database
- The IP addresses that have been automatically mapped to the MAC addresses of hosts are found in the DHCP binding database in the DHCP server.
- An address conflict occurs when two hosts use the same IP address. During address assignment, the DHCP server checks for conflicts. If a conflict is detected, the address is removed from the pool. The address will not be assigned until the administrator resolves the conflict.
DHCP address pools
- A DHCP address pool can be configured with a name that is a symbolic string (such as "cabo") or an integer (such as 0).
- Configuring a DHCP address pool also puts the router into DHCP pool configuration mode, where the pool parameters can be configured.
- If the DHCP server address is part of a configured DHCP address pool, you must exclude the DHCP server address from the network pool.
- While in DHCP server pool configuration mode, the system will place the DHCP server pool in pending mode and the DHCP server will not use the address pool to distribute information to clients. To activate the pool, use the deploy command.
- DHCP options are supported on a per-pool basis as required by the DHCP clients to be serviced in the sub-network.
- DHCP defines a process by which the DHCP server knows the IP subnet in which the DHCP client resides, and the DHCP server can assign an IP address from a pool of valid IP addresses in that subnet.
If the client is directly connected (the giaddr field is zero), the DHCP server matches the DHCP DISCOVER message with DHCP pools that contain the subnets configured on the receiving interface. If the client is not directly connected (the giaddr field of the DHCP DISCOVER message is not zero), the DHCP server matches the DHCP DISCOVER message with a DHCP pool that has the subnet that contains the IP address in the giaddr field.