Specific process of DHCP relay Fault Handling

We have learned a lot about the content of the DHCP protocol. In this case, we have also explained some processes and methods for troubleshooting DHCP server faults. Here we will focus on the DHCP relay fault handling process. I hope this will help you.

DHCP relay troubleshooting ◆ typical Networking Environment

Shows the typical networking of DHCP relay. DHCP relay troubleshooting will be based on this network.

Figure DHCP relay typical networking applications

In this network diagram:

● The Client DHCP Client) and the DHCP Server are not in the same LAN. The Client uses DHCP to relay the routeport and connect to the DHCP Server.

● The routerinterface GigabitEtherneternet1/0/0 is connected to the client. The interface enables DHCP relay and configures the DHCP server address proxy for this interface.

● The routeinterface GigabitEthernet1/0/1 is connected to the DHCP server interface GigabitEthernet2/0/0. Assume that the IP address range of the client is 10.110.0.0 and the IP address range of the DHCP server is 255.110.0.0. the DHCP server must use DHCP relay to assign an IP address range of 10.110.0.0 to the client.

DHCP relay troubleshooting ◆ configuration considerations

DHCP relay troubleshooting ◆ fault diagnosis process

The client cannot obtain the IP address through DHCP relay for the network shown in. Use the following fault diagnosis process, as shown in.

Figure DHCP relay Fault Diagnosis Flowchart

DHCP relay troubleshooting ◆ troubleshooting steps

Procedure

1. check whether a route exists between the DHCP relay router interface and the DHCP Server.

After configuring IP addresses 10.110.1.1 and 255.110.1.1 on the interfaces of GigabitEthernet1/0/0 and interfaces of GigabitEthernet2/0/0, run the ping route 110.1.1 command on the routeside and ping 10.110.1.1 on the DHCP server, check whether the ping is successful.

If the ping fails, run the "display ip routing-table" command on the router interface and the DHCP server to check whether the route table entry at the peer end exists.

If not, run the ip route-static route 110.1.1 16 gigabitethernet 1/0/1 command and the ip route-static 10.110.1.1 16 gigabitethernet 2/0/0 command on the routerrouters and DHCP servers to add static routes.

If ping is still unavailable, check whether the physical line is normal.

2. Check the configuration of the relay agent.

Check whether the DHCP server ip address of the relay proxy is configured. That is, check whether the ip relay address has 110.1.1 configured on the GigabitEthernet1/0/0 interface. Use the display current-configuration command in the System View to check whether DHCP is enabled.

3. View DHCP server configurations

● Run the "display dhcp server tree all" command to check whether the global address pool is configured and the IP address range involved in the dynamic allocation.

● Check whether the CIDR Block of the IP address involved in the dynamic allocation and the IP address of interface GigabitEthernet1/0/42 are in the same CIDR block. In this example, check whether it is configured as network 10.110.0.0 mask 255.255.0.0.

4. check whether there are available IP addresses in the address pool.

● Run the display dhcp server free-ip command to check whether an available ip address exists in the address pool.

● If no available IP address exists, run the display dhcp server expired pool command to check whether there is an IP address that has expired the lease.

● If there is no IP address that has expired the lease, run the display dhcp server conflict all command to check whether there is a conflicting IP address. If yes, check whether the probe time is more than one hour. In the implementation of NE80E/40E, if a conflicting IP address is found, the IP address can be re-allocated after 1 hour.

After performing the preceding steps, if the available IP addresses, expired IP addresses, and conflicting IP addresses in the address pool do not exist, the addresses in the address pool are exhausted and you can create a global address pool, the CIDR blocks of the IP addresses involved in the dynamic allocation in this address pool must overlap with those of the IP addresses involved in the dynamic allocation in the previously configured address pool, and the CIDR block is larger than the IP address segment of the IP address pool used for dynamic allocation.

If an available IP address is found during the above steps, and the configuration and physical line are normal, but the client still cannot obtain the IP address, contact the Huawei Technical Support Engineer.

The above is all about the DHCP relay fault handling process.