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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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Protocol Status of a PPP Interface Is Down

Protocol Status of a PPP Interface Is Down

Common Causes

After an interface is configured with PPP, LCP negotiation fails, which causes the protocol status of the interface to be Down.

This fault is commonly caused by one of the following:

  • PPP configurations on the two ends of the link are incorrect.

  • The physical status of the interface is Down.

  • PPP packets are discarded.

  • A loop occurs on the link.

  • The link delay is too long.

Troubleshooting Flowchart

The troubleshooting roadmap is as follows:

  • Check that PPP configurations on the two ends of the link are correct.

  • Check that the physical status of the interface is Up.

  • Check that the interface can sent and receive protocol packets.

  • Check that the link is loop-free.

  • Check that the link delay is tolerant.

Figure 17-10 shows the troubleshooting flowchart.

Figure 17-10  Troubleshooting flowchart for an LCP negotiation failure

Troubleshooting Procedure

NOTE:

Saving the results of each troubleshooting step is recommended. If your troubleshooting fails to correct the fault, you will have a record of your actions to provide Huawei technical support personnel.

Procedure

  1. Check that PPP configurations on the two ends of the link are correct.

    Run the display this command in the view of the interface whose protocol status is Down to check PPP configurations.

    [Huawei-Serial2/0/0] display this
    #
    interface Serial2/0/0
     link-protocol ppp
     undo shutdown
     ip address 10.10.1.1 255.255.255.0
    #
    return 
    

    • Check whether the following configurations on the two ends match each other. If not, modify the configuration referring to the chapter "PPP and MP Configuration" in the AR100&AR120&AR150&AR160&AR200&AR1200&AR2200&AR3200&AR3600 Configuration Guide - WAN Access.

      • Check whether the authenticator and authenticatee are configured with the same authentication mode. The ppp authentication-mode authentication-mode command indicates the authentication mode adopted by the local end that functions as the authenticator. You need to check the authentication mode adopted by the peer. For example, if the ppp pap local-user user-name password simple password command has been configured, it means that the peer adopts PAP authentication.

      • Check whether both ends are bundled into an MP-group or neither of the two ends is bundled into an MP-group. If one end has been bundled into an MP-group, the other end must be bundled into the same MP-group. If the ppp mp interface-type interface-number command is configured, it means that the interface has been bundled into an MP-group.

      • Check whether the authenticator and authenticatee are configured with the same password for PPP authentication.

        • If PAP authentication is adopted, do as follows to check the configured user name and password:

          Check the user name and password of the authenticatee in the interface view.

          [Huawei-Serial2/0/0] display this
          #
          interface Serial2/0/0
           link-protocol ppp
          ppp pap local-user huawei password simple huawei
           undo shutdown
          #
          return
          

          Check the user name and password of the authenticator in the AAA view.

          [Huawei] aaa
          [Huawei-aaa] display this
          #
          aaa
           local-user huawei password cipher %$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
          #
          return
          
        • If the authenticator adopts CHAP authentication and is configured with a user name, do as follows to check the user name and password:

          Check the user name of the authenticatee in the interface view, and then check the password in the AAA view based on the user name.

          [Huawei-Serial2/0/0] display this
          #
          interface Serial2/0/0
           link-protocol ppp
          ppp chap user huawei
           undo shutdown
          #
          return
          [Huawei-Pos1/0/0] aaa
          [Huawei-aaa] display this
          #
          aaa
           local-user huawei password cipher %$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
          #
          return
          

          Check the user name and password of the authenticator in the AAA view.

          [Huawei] aaa
          [Huawei-aaa] display this
          #
          aaa
           local-user huawei password cipher %$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
          #
          return
          
        • If the authenticator adopts CHAP authentication but is not configured with a user name, do as follows to check the user name and password:

          Check the user name and password of the authenticatee in the interface view.

          [Huawei-Serial2/0/0] display this
          #
          interface Serial2/0/0
           link-protocol ppp
           ppp chap user huawei
           ppp chap password simple huawei
           undo shutdown
          #
          return
          

          Check the user name and password of the authenticator in the AAA view.

          [Huawei] aaa
          [Huawei-aaa] display this
          #
          aaa
           local-user huawei password cipher %$%$t"}TJ~\;SKu%wY$mKGdY%*!u%$%$
          #
          return
          
    • If the preceding configurations are correct but the fault persists, go to Step 2.

  2. Check that the physical status of the interface is Up.

    Run the display interface interface-type interface-number command to check the physical status of the interface.

    • If the physical status of the interface is Down, you need to rectify the physical fault of the interface. For detailed troubleshooting procedures, see "Physical Interconnection Troubleshooting".

    • If the physical status of the interface is Up but the fault persists, go to Step 3.

  3. Check that the interface can sent and receive protocol packets.

    Run the display interface interface-type interface-number command to check the number of sent packets and received packets to determine whether the interface sends and receives protocol packets.

    [Huawei] display interface Serial 2/0/0
    Serial2/0/0 current state : UP
    Line protocol current state : UP
    Last line protocol up time : 2010-02-05 06:35:43
    Description:HUAWEI, AR Series, Serial2/0/0 Interface
    Route Port,The Maximum Transmit Unit is 4470, Hold timer is 10(sec)
    Internet Address is 1.1.1.2/24
    Link layer protocol is PPP
    LCP opened, IPCP opened
    The Vendor PN is HFBR-57E0P
    The Vendor Name is AVAGO
    Port BW: 155M, Transceiver max BW: 155M, Transceiver Mode: MultiMode
    WaveLength: 1310nm, Transmission Distance: 2000m
    Physical layer is Packet Over SDH
    Scramble enabled, clock master, CRC-32, loopback: none
    Flag J0 "NetEngine       "
    Flag J1 "NetEngine       "
    Flag C2 22(0x16)
        SDH alarm:
            section layer:  none
            line    layer:  none
            path    layer:  none
        SDH error:
            section layer:  B1 0
            line    layer:  B2 0  REI 44
            path    layer:  B3 0  REI 23
    Statistics last cleared:never
        Last 300 seconds input rate 24 bits/sec, 0 packets/sec
        Last 300 seconds output rate 24 bits/sec, 0 packets/sec
        Input: 70945 packets, 1135144 bytes
        Input error: 0 shortpacket, 0 longpacket, 0 CRC, 0 lostpacket
        Output: 70945 packets, 1135140 bytes
        Output error: 0 lostpackets
        Output error: 0 overrunpackets, 0 underrunpackets     
    

    • If the number of received or sent packets is 0, or the number does not increase, it indicates that packets are discarded during transmission. Check whether the physical connection is correct. For detailed information, see "Physical Interface Cannot Go Up".

    • If the physical connection is correct, you need to locate the cause of packet loss. For detailed troubleshooting procedures, see "Packet Loss Troubleshooting".

    • If packets can be received and sent but the fault persists, go to Step 4.

    Debugging affects the system performance. Therefore, after debugging, run the undo debugging all command to disable it immediately.

    In addition, you can run the debugging ppp all interface interface-type interface-number command to check the number of sent and received protocol packets and the status changes of the PPP state machine.

    Jun  2 2010 17:19:41.310.1 Huawei PPP/7/debug2:Slot=1;
      PPP Event:
          Serial2/0/0 LCP TO+(Timeout with counter > 0)  Event
          state acksent , Retransmit = 4
    Jun  2 2010 17:19:41.310.2 Huawei PPP/7/debug2:Slot=1;
      PPP Packet:
          Serial2/0/0 Output LCP(c021) Pkt, Len 18
          State acksent, code ConfReq(01), id 3, len 14
          MRU(1), len 4, val 1176
          MagicNumber(5), len 6, val 00abb891
    Jun  2 2010 17:19:41.310.1 Huawei PPP/7/debug2:Slot=1;
      PPP Packet:
          Serial2/0/0 Input  LCP(c021) Pkt, Len 18
          State acksent, code ConfAck(02), id 3, len 14
          MRU(1), len 4, val 1176
          MagicNumber(5), len 6, val 00abb891
    Jun  2 2010 17:19:41.310.2 Huawei PPP/7/debug2:Slot=1;
      PPP Event:
          Serial2/0/0 LCP RCA(Receive Config Ack)  Event
          state acksent                 
    

  4. Check that the link is loop-free.

    Run the display interface interface-type interface-number command to check the physical status of the interface.

    [Huawei] display interface Serial 2/0/0
    Serial2/0/0 current state : UP
    Line protocol current state : DOWN
    Description:HUAWEI, AR Series, Serial 2/0/0 Interface
    Route Port,The Maximum Transmit Unit is 4470, Hold timer is 10(sec)
    Internet protocol processing : disabled
    Link layer protocol is PPP, loopback is detected
    LCP closed
    The Vendor PN is HFBR-57E0P
    The Vendor Name is AVAGO
    Port BW: 155M, Transceiver max BW: 155M, Transceiver Mode: MultiMode
    WaveLength: 1310nm, Transmission Distance: 2000m
    Physical layer is Packet Over SDH
    Scramble enabled, clock master, CRC-32, loopback: local
    Flag J0 "NetEngine       "
    Flag J1 "NetEngine       "
    Flag C2 22(0x16)
        SDH alarm:
            section layer:  none
            line    layer:  none
            path    layer:  none
        SDH error:
            section layer:  B1 22
            line    layer:  B2 94  REI 145
            path    layer:  B3 44  REI 86
    Statistics last cleared:never
        Last 300 seconds input rate 56 bits/sec, 0 packets/sec
        Last 300 seconds output rate 56 bits/sec, 0 packets/sec
        Input: 40530 packets, 890400 bytes
        Input error: 0 shortpacket, 0 longpacket, 2 CRC, 0 lostpacket
        Output: 36512 packets, 946612 bytes
        Output error: 0 lostpackets
        Output error: 0 overrunpackets, 0 underrunpackets
    

    • If loopback is detected is displayed, it indicates that a loop occurs on the link. You need to locate the cause of the loop and eliminate the loop.

    • If no loop occurs but the fault persists, go to Step 5.

  5. Check that the link delay is tolerant.

    Use a tester to test the link delay. On a Huawei router, the transmission of a PPP packet times out in 3 seconds, and the timeout period is configurable. The link delay must be smaller than the timeout period.

    • If the link delay is too long, replace or maintain the relevant device.

    • If the link delay is tolerant but the fault persists, go to Step 6.

  6. Collect the following information and contact technical support personnel.

    • Results of the preceding troubleshooting procedure

    • Configuration files, log files, and alarm files of the devices

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Updated: 2019-05-10

Document ID: EDOC1000079719

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