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

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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.

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

IP addresses are obtained slowly on the AR
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.

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.

Why cannot a device learn the ARP entries of directly connected PCs
By default, strict ARP learning is enabled on fixed switches. A fixed switch sends an ARP request to a client and learns ARP entries only after receiving an ARP reply from the client. PCs that have wireless network interface cards (NICs) installed do not reply to the ARP requests received from the switch. As a result, the switch cannot learn ARP entries of these PCs. These PCs reply to the ARP requests only after their wireless NICs are restarted. To solve the problem, run the undo arp learning strict command in the system view to disable strict ARP learning.

An S series switch fails to ping the remote device using ping packets carrying the source IP address. Why the ping succeeds after the source IP address is changed
For S series switches (except the S1700), the possible reason why the ping succeeds after the source IP address is changed is that the remote device does not have a return route to send response packets. If the ping succeeds after you change the source IP address or do not specify any source IP address in the ping command, you need to check whether the remote device has a return route.

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