How does DHCP fail to find a reason?

First: Check the physical connection is unblocked.

Configure the IP address on the network adapter connected to the client and the server to ensure that the IP address gigabitethernet1/0/0 the server-side interface is on the same network segment. Ping gigabitethernet1/0/0 interface from the client IP address, if you can ping, then the connection is unblocked, then the physical line failure can be excluded. You can also turn on the DHCP debug switch on the server side to see if you can receive the client's DHCPDiscover message.

　　Second: The DHCP server is configured correctly.

1. Execute command DHCP enable.

2. Execute command display DHCP server tree all, see if the global address pool exists, and the IP address in the address pool gigabitethernet1/0/0 the IP address of the interface is in the same network segment. If it does not exist, execute the command DHCP server ip-pool pool-name and command network ip-address [mask {mask}] to create an address pool and configure the range of dynamically assigned IP addresses in the address pool. If the address pool exists, but the IP address in the address pool is not in the same network segment as the interface gigabitethernet1/0/0, modify the IP address in the address pool or modify the IP address of the interface gigabitethernet1/0/0 so that they are in one network segment.

3. Execute command DHCP Select global {all interface Interface-type Interface-number} in System view or EXECUTE command DHCP in gigabitethernet1/0/0 interface view Sele CT Global to ensure that customers under gigabitethernet1/0/0 get addresses from the global address pool.

　　Third: whether there are available IP addresses, expired IP addresses, or conflicting IP addresses within the address pool.

1. Execute command display DHCP server FREE-IP to check if there are any available IP addresses in the global address pool.

2. If no address is available, execute the command display DHCP server expired pool pool-name to see if there is an expired IP address.

3. If no expired IP address exists, execute command display DHCP server conflict all to see if there is a conflicting IP address. If so, see if the probe time (Discover times) has exceeded 1 hours. In the ne80e/40e implementation, if a conflicting IP address is found, we can reassign this IP address after 1 hours. When a conflicting IP address exists and the probe time does not exceed 1 hours, the Execute command reset DHCP server conflict all releases the conflicting IP address. If there is no conflicting IP address, the available IP address in the address pool, the expired IP address, and the conflicting IP do not exist, indicating that the IP address in the address pool has been exhausted and you can recreate a global address pool that overlaps the network of the address pool and the network of the previous address pool, And the network segment is greater than the network segment of the former address pool.