A directly connected device cannot be pinged or a client obtains an IP address slowly using DHCP. How is this problem solved

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STP prevents loops on Layer 2 networks. By default, STP is enabled on the AR router. When the AR router functions as the user access device (the WAN-side uplink connects to the Internet and the LAN-side downlink connects to the internal network), loops do no occur. If STP is enabled, network flapping may occur due to port blocking or slow STP convergence. As a result, device functions are affected. It is recommended that the stp disable command be used in the system view to disable STP.

Other related questions:
The reason why a device directly connected to an AR router cannot be pinged or the IP address of the device that is obtained over DHCP is returned slowly
In Layer 2 networks, STP can solve network loop problems. By default, this function is enabled on an AR router. If the AR router is used as a user access device (the WAN interface of the router is connected to the Internet, and the LAN interface is connected to an intranet), there is no risk of loop generally. In this case, you are advised to run the stp disable command to disable STP and avoid interface blockage due to the enabled STP function or network flapping due to STP convergence. For example, a device directly connected to an AR router cannot be pinged or the IP address of the device that is obtained over DHCP is returned slowly.

DHCP clients cannot obtain IP addresses. How do I solve this problem
Ensure that the DHCP configuration is correct, and reduce the IP address lease. If a long IP address lease is set, after all addresses in the address pool are allocated, addresses that are not required cannot be released immediately. As a result, other DHCP clients cannot obtain IP addresses.

Why does a user on an AR slowly obtain an IP address
The cause is that the interface is enabled with STP. By default, all interfaces of an AR are configured with STP. When the interface changes from Down to Up, STP convergence is performed (the process takes about 30s). During STP convergence, an interface on an AR directly discards received packets. That is, DHCP Request messages are all discarded during the STP convergence period. IP addresses are obtained slowly in this case. Use either of the following methods to solve this problem: - Run the stp edged-port enable command on the AR interface connected to a user terminal to configure the interface as an edge interface. If the AR is configured with the stp bpdu-protection command, the edge interface of the AR becomes Down when there are malicious attacks of BPDUs. To enable the edge interface to automatically go Up, run the error-down auto-recovery cause bpdu-protection interval interval-value command. - If there is no physical loop, run the stp disable command on the AR in the system view or the AR interface connected to a user terminal.

An AR used as a DHCP client cannot obtain an IP address
When the configuration is correct, you can shorten the IP address lease. If the IP address lease is long, after addresses in the address pool are allocated, the address that has been allocated to a client is no longer used and cannot be released. As a result, other DHCP clients cannot obtain the IP address.

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.

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