IP addresses are obtained slowly on the AR

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The cause is that the interface is enabled with STP. By default, all interfaces on 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 view of the AR interface connected to a user terminal to disable the STP function.


For details about client's failure to obtain and IP address, see the Revelations of Troublesolving on the right page.

Other related questions:
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.

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.

IP address obtained by a client on the AR conflict with the IP address of another client
The troubleshooting roadmap and solution are as follows: -Possible causes: The IP address is configured manually for the host, and is not excluded from the address pool when the DHCP server is deployed. -Troubleshooting: Disable the network adapter of the client or disconnect network cables and perform the ping operation on another host to check whether the host assigned with the IP address exists. After receiving a response, the IP address is configured manually. -Solution: a. Modify the manually configured IP address of the host. b. Exclude the conflicting IP address from the address pool on the DHCP server.

How do I check IP addresses that are dynamically obtained by an AR
On the AR, you can run the following command to check the IP address that is dynamically obtained. - If IP addresses are assigned based on the interface address pool, run the display ip pool interface interface-pool-name used command. If the IP addresses are assigned based on the global address pool, run the display ip pool name ip-pool-name used command. You can know the IP address assigned to each client based on the mapping between IP addresses and MAC addresses.

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.

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