The PPPoE physical interface is Up but the state of the protocol is Down

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After a PPPoE dialup, all services are born on the Dialer interface, with corresponding physical interface being Up and protocol being Down, which is normal and does not affect the services and use. Ignore it.
A virtual interface is needed for PPPoE dialup to bear all services. Pay attention to the Dialer interface, and the protocol status does not need to be concerned with.

Other related questions:
The physical state of a serial interface is Up but the protocol state of the interface is Down
For the problem that the physical state of a serial interface is Up but the protocol state of the interface is Down, see the troubleshooting guide. For details, access the URL in the right column.

The state of the E1 interface of an AR router is not Up
If the state of the E1 interface of an AR router is not Up, perform the following steps: 1. If the physical state of the interface is not Up, check the physical cables. - If coaxial cables are used for the communication between devices, exchange the sending cable and receiving cable. - If balanced cables are used for the communication between devices, check whether line order of the cables is correct. The line order of the DB9 connector on the card: Line 1 and line 2 are the receiving lines. Line 6 and line 7 are the transmitting lines. The line order of the RJ45 connector used by balanced cables: Line 1 and line 2 are the transmitting lines. Line 4 and line 5 are the receiving lines. 2. Check whether the configuration of the E1 interface is consistent with that of the interconnected physical interface. - Enter the Controller interface view and run the display this command to check the configuration of the Controller interface. - Check whether the physical attributes of the Controller interfaces on both ends are consistent, such as the frame format, coding format, data inversion, cable impedance, and timeslot number. - The clocks at both ends must work in master/slave mode. - If the configurations of the interfaces are not consistent, or the state of the interface alternates between Up and Down, configure the interfaces on both ends again. - If the configurations of the interfaces on both ends are consistent and meet the requirements above, and if the physical state of the interface keeps Up stably, perform step 3. 3. Check whether the configurations of the serial interfaces on both ends are consistent. - Enter the serial interface view and run the display this command to check the configuration of the serial interface. - Check whether the attributes of the serial interfaces on both ends are consistent, such as the encapsulation and CRC methods. If the PPP authentication method is used, check whether the authentication methods used by both ends are consistent, whether the user names and passwords are correct, and whether the FR-DLCI configurations are consistent. In addition, check whether the serial interfaces are shut down. - If the configurations of the serial interfaces on both ends are not consistent, configure the serial interfaces again. - If the interface cannot send and receive data properly even if the configurations of the serial interfaces on both ends are consistent, perform step 4. 4. Check whether the serial interfaces transmit and receive data. - Enter the views of the serial interfaces and run the display this interface command to check whether the serial interfaces on both interconnected ends transmit data. - If the serial interfaces do not transmit data, the negotiation packet in the upper layer is not sent properly. In this case, try to run the shutdown command or undo shutdown command to trigger the sending of the negotiation packet in the upper layer. - If the serial interfaces transmit and receive data, perform step 5. 5. Check whether the data transmitted or received by the serial ports includes error packets. - Enter the views of the serial interfaces and run the display this interface command to check whether the data received by the serial interfaces on both interconnected ends includes a large number of CRC error packets and whether the number of error packets increases. - If the data received by the serial interfaces includes a large number of CRC error packets, check whether the cables are connected firmly. For the problem that the state of an E1 interface of an AR router is not Up, see the troubleshooting guide. For details, access the URL in the right column.

The state of an E1 interface is not Up when the interface interconnects with the peer device
For the problem that the state of an E1 interface of an AR router is not Up when the interface interconnects with other devices, see the troubleshooting guide. For details, access the URL in the right column.

What can I do if an interface on a PPPoE client frequently alternates between Up and Down states

The possible causes are as follows:

    -The IP address assigned to the interface by the PPPoE server is the same as that of another interface on the PPPoE client.

    Solution: Change the conflicting IP address on the PPPoE client or run the remote address command on the PPPoE server to change the IP address assigned to the interface.

  • -All IP addresses in the address pool on the PPPoE server have been allocated to PPPoE clients and no IP address is available for this interface.

    Solution: Run the network (IP address pool view) command in the IP address pool view on the PPPoE server to expand the IP address range of the IP address pool.


What does it means if the physical interface state of a 3G Cellular interface is Down
If the physical state of a 3G Cellular interface is Down, the 3G link is not established at the time and the data service does not run yet, which means that the dial-up is not performed or fails on the 3G link. In this case, the physical interface state of the 3G Cellular interface is down even a 3G data card (3G modem) is inserted into the device.

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