The most vital DHCP service in a computer network, the skills to do DHCP troubleshooting are equally important for network administrators

At first glance

In a computer network infrastructure in an organization, among the important components of the support is the DHCP server. For that, it is very urgent for network administrators to be able to troubleshoot the DHCP server against any format of the problem related to the DHCP server, both the problems that arise due to configuration errors and DHCP installation, to the small problems that affect a computer that cannot receive an IP address from This DHCP server.

Verify the configuration of clients

One indication of failure of a DHCP is if a computer / client loses connection to the network resource-2 or if a client computer cannot get a connection to the network one time. Our choice is to make sure whether this comes from a DHCP server, from the client itself, or from another source.

Make sure the client accepts IP

One of the techniques for starting DHCP troubleshooting is from the client to ensure that the client receives an IP address from the DHCP server. You can do the “ipconfig / all” command line from the DOS prompt c: \> (if from Windows press the Windows key and R together, continue to type CMD and press Enter). Can be ignored the output of “ipconfig / all” indicates that there is a DHCP enabled = YES. This means that the TCP / IP configuration has been configured to receive an automatic IP address, and if the DHCP server is located then the client should be able to receive the IP address configuration from the DHCP server.

Or you can click on the computer image in the lower right corner and select the Support tab, you can note if a computer can accept the configuration from the DHCP server then the Connection status is “Address Type” = “Assigned by DHCP” (see picture)

Troubleshooting DHCP server

Use the “repair” button

In the picture shown that the computer still does not connect, it can be clicked on the “Repair” button. Or if you are one time watching a yellow triangle sign that does not accept the configuration from the DHCP server, then click on the “Repair” sign.

Do you know what the computer is doing with this “Repair” command?

There are 6 stages implemented by Windows when working on the “Repair” process, as follows:

1. Do DHCP request messages to work on updating IP address leases. This is similar to the command “ipconfig / renew”
2. Removing the ARP cache, this stage is the same as if we type the “arp -d” command
3. Removing NETBIOS cache, which is the same as if we are working on “nbtstat -R” in the command prompt
4. Delete DNS cache, which is the same as the command prompt “ipconfig / flushdns”
5. Re-register the NetBIOS name and IP address with the WINS server. this step is the same as the command prompt “nbtstat -RR”
6. Register the computer name and IP address of the client computer for the DNS server and the same as the command prompt “ipconfig / registerdns”

If the client is able to accept an IP address that matches the network and there is no message Warning there is an IP conflict, it can be considered that the client does not have a problem with the IP address.

Troubleshooting DHCP – IP Conflict

If the client is submitted an IP address that turns out to have been used by a different client on the same local network, a warning message will occur when the address conflict is present. we can also check the event viewer for this conflict address like the picture above.

If this IP address is from a DHCP server, then this business is a sign of a different DHCP on your network, or re-deployment from the DHCP scope suddenly-2.

Track other DHCP servers

To be sure, the dhcploc.exe command (found in Windows Support Tool) can be used to track the presence of foreign DHCP on the network (because there may be idle for DHCP servers). After you have assured the other DHCP server has been turned off, one time first raise the “conflict detection attempt” to update the client with the command “ipconfig / renew” or click “repair”. Or you can also use the command line “shutdown / i” to restart a number of remote computers at once.

Failure to find an IP from a DHCP server

If you find the output from “ipconfig / all” indicates the IP address of APIPA (169.254.0.1 to 169.254.255.254), or from alternate configuration, one time do “ipconfig / renew” or click “repair”. If the results are the same, this business indicates:

1. There is no DHCP server / DHCP relay agent in the broadcast range
2. Disconnect the DHCP server connection
3. DHCP server scope is problematic

How can you make sure there is a DHCP server in the broadcast range? Because IP clients are obtained from the APIPA IP address, you cannot ping the DHCP server because of another network. APIPA in the range 169.254.0.0 – 169.254.254.254 with subnet mask 255.255.0.0. then you must submit a static IP address to the client computer that has this problem with the IP in the same address range as the DHCP server.

Use “netsh dhcp show”

If a static IP address has been configured, then you can ping the DHCP server. If you do not understand the DHCP server IP address, then at the command prompt, type “netsh dhcp show”. if the ping results to the DHCP server are successful – it means that the connection to the DHCP server is not a problem. If it can be ascertained that both points 1 and 2 do not have a problem, then suspicion can be due to the configuration of the scope of the DHCP server’s IP address.

If all clients do not find an IP address, make sure that:

1. The DHCP server installation is perfect
2. The DHCP server configuration is perfect
3. Authorized was successful, must be from the Enterprise user admin or member Enterprise in your domain’s active directory.

To ensure the IP address scope is not problematic, then make sure that the active and non-ending scope is all used by clients. You can do the following:

• Re-authorized if necessary.
• Deactivate the scope then activekan again.
• If the scope quickly runs out, reduce the duration of the lease time. This will accelerate the release of IPs borrowed by clients (especially those who are not active).
• If the client fails, besides ensuring connection to DHCP is OK, make sure that UDP 67 and UDP 68 ports are not blocked

Sometimes a PC cannot also get an IP address configuration from a DHCP server even though the TCP / IP configuration has been set up to automatically receive an IP address. This often happens on computers that are used up on an internet connection configuration with ICS (Internet Connection Sharing). You must lure it first by submitting a static / manual IP address in the same range as the DHCP server. after that try pinging the DHCP server, if successful, return the configuration to “Obtain IP address automatically” and restart the PC, or rather do “ipconfig / renew” or click “repair”.