Failure to obtain IP addresses from DHCP server

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For S series switches (except S1700 switches), a client may fail to obtain an IP address from the DHCP server due to the following:
- Incorrect configuration
- No available IP address in the address pool
- STP enabled on the upper-layer access device of diskless workstations
For the fault locating and troubleshooting procedure, see the section "A Client Fails to Obtain an IP Address from a DHCP Server" in Configuration Guide �?IP Service.

Other related questions:
DHCP clients fail to obtain IP addresses from the DHCP server on the AR
The causes that DHCP clients fail to obtain IP addresses from the DHCP server are as follows: - The configuration is incorrect. - There is no allocable IP address in the DHCP address pool. - STP is enabled on upper-level access devices of some diskless workstations. For details on troubleshooting and solutions, see AR150&AR160&AR200&AR510&AR1200&AR2200&AR3200 FAQ.
About the AR ClientExceptions occurs when the IP address is obtained. For details, see the Revelations of Troublesolving on the right page.

DHCP client cannot obtain a correct IP address
The request packets (DHCP discover) are broadcast by the DHCP clients. If multiple DHCP servers are located on the same subnet (for example, bogus DHCP server), the clients may obtain IP addresses from a bogus DHCP server. To address this problem, configure DHCP snooping. Then clients can receive DHCP packets from only the trusted DHCP server. Perform the following configuration: [Huawei] dhcp enable [Huawei] dhcp snooping enable [Huawei] interface gigabitethernet 1/0/1 //Enter the view of the interface connected to the DHCP client. [Huawei-GigabitEthernet1/0/1] dhcp snooping enable [Huawei-GigabitEthernet1/0/1] quit [Huawei] interface gigabitethernet 1/0/2 [Huawei-GigabitEthernet1/0/2] dhcp snooping trusted //Configure the interface of the DHCP server as the trusted interface. [Huawei-GigabitEthernet1/0/2] quit Note: - When you configure DHCP snooping on a Layer 2 access device, steps 1, 2, and 3 are mandatory and must be performed in the following sequence. - When you configure DHCP snooping on a DHCP relay agent, only steps 1 and 2 are required.

Can the terminal with dual network adapters obtain IP addresses from the active and standby DHCP servers
When S series switches excluding the S1700 function as DHCP servers, the terminal with dual network adapters cannot obtain IP addresses from the active and standby DHCP servers.

Reasons why the PC that has obtained an IP address from the DHCP server cannot access the Internet on S series switch
For S series switches (exclude S1700 switches), in normal situations, a PC can access the Internet after obtaining an IP address through DHCP. However, if the IP address is assigned by a bogus DHCP server, the PC cannot access the Internet with the incorrect IP address. If this problem occurs, you are advised to configure DHCP snooping on the Layer 2 access device or first DHCP relay agent from the device, to ensure that PCs can obtain correct IP addresses. - When you configure DHCP snooping on a Layer 2 access device, steps 1, 2, and 3 are mandatory and must be performed in sequence. - When you configure DHCP snooping on a DHCP relay agent, only steps 1 and 2 are required. 1. Enable DHCP snooping globally. [HUAWEI] dhcp enable [HUAWEI] dhcp snooping enable 2. Configure the interfaces connected to DHCP clients. Perform the configuration on all interfaces connected to DHCP clients. GE0/0/1 is used as an example. [HUAWEI] interface gigabitethernet 0/0/1 [HUAWEI-GigabitEthernet0/0/1] dhcp snooping enable [HUAWEI-GigabitEthernet0/0/1] quit 3. Perform the configuration on interfaces connected to the DHCP server. GE0/0/2 is used as an example. [HUAWEI] interface gigabitethernet 0/0/2 [HUAWEI-GigabitEthernet0/0/2] dhcp snooping trusted [HUAWEI-GigabitEthernet0/0/2] quit

Method used to configure DHCP relay on the AR
When the DHCP server and DHCP clients are on different network segments, the DHCP relay agent can be configured so that the DHCP server can assign IP addresses to the DHCP clients. Procedure: 1. Configure the router # sysname Router # dhcp enable //Enable the DHCP function. # ip pool ip-pool1 gateway-list 10.10.1.1 //Set the gateway IP address. network 10.10.1.0 mask 255.255.255.128 //Specify the range of IP addresses that can be dynamically allocated in the global address pool. excluded-ip-address 10.10.1.2 //Set the IP address 10.10.1.2 that is not assigned automatically in the address pool. excluded-ip-address 10.10.1.4 //Set the IP address 10.10.1.4 that is not assigned automatically in the address pool. dns-list 10.10.1.2 //Configure the IP address of the DNS server for the DHCP client. nbns-list 10.10.1.4 //Configure the IP address of the NetBIOS server for the DHCP client. lease day 10 hour 12 minute 0 //Set the IP address lease to 10 days and 12 hours. domain-name huawei.com //Set the domain name to huawei.com. static-bind ip-address 10.10.1.5 mac-address fc12-2567-ce34 //Assign a fixed IP address to the PC_AD. # ip pool ip-pool2 gateway-list 10.10.1.129 //Set the gateway IP address. network 10.10.1.128 mask 255.255.255.128 //Specify the range of IP addresses that can be dynamically allocated in the global address pool. dns-list 10.10.1.2 //Configure the IP address of the DNS server for the DHCP client. lease day 5 hour 0 minute 0 //Set the IP address lease to 5 days. domain-name huawei.com //Set the domain name to huawei.com. # interface GigabitEthernet0/0/0 ip address 10.10.1.1 255.255.255.128 dhcp select global //Configure the global address pool mode. # interface GigabitEthernet0/0/1 ip address 10.10.1.129 255.255.255.128 dhcp select global //Configure the global address pool mode. 2. Verify the configuration. Run the display ip pool command on the router to check the IP address pool configuration.

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