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The ATM PWE3 have misorder packets in public network lead to ATM packet loss problem

Publication Date:  2014-12-29 Views:  37 Downloads:  0
Issue Description

Version information :

NE40E & 80E CX600 V6R3C00SPCa00 , NE40E & 80E CX600 V6R5C00SPC900 , NE40E & 80E CX600 V6R6C00SPC300 , NE40E & 80E CX600 V6R7C00SPC300

Network topology:

The typical ATM PWE3 Scene topology as shown in the following figure.

Problem Description:

After configure the ATM PWE3 service, customer find the ATM service of CE have packet loss. They try ping test and find ping lost. The service is interrupted. 

Handling Process

1.      There are lots of ATM service packets loss on both CE1 and CE2 side. The A4CF card have four ATM ports, and the ATM1/0/0 and ATM1/0/1 were not used. In order to simplify the problem, we put the two ports fiber loopback. We configure IP in ATM1/0/0.1000, and configure ATM PWE3 in ATM1/0/1.1000. The network topology as below:


2.      In the network topology, we ping 10 packets from the ATM1/0/0.1000 of NE80E. The ping loss happen, only 1 ping packet is OK.

[_NE80E-diagnose]ping -c 10

  PING 56  data bytes, press CTRL_C to break

    Request time out

    Request time out

    Request time out

    Request time out

    Request time out

    Request time out

    Request time out

    Request time out

    Reply from bytes=56 Sequence=9 ttl=255 time=139 ms

    Request time out


  --- ping statistics ---

    10 packet(s) transmitted

    1 packet(s) received

    90.00% packet loss

    round-trip min/avg/max = 139/139/139 ms


3.      Then we check the ATM interface statistic to find where the packets are lost. The ATM3/0/0.1000 of NE80E sent 10 ping packets.

[NE80E-diagnose]display interface atm3/0/0.1000

    1 packets input, 92 bytes, 0 drops

    10 packets output, 1590 bytes, 0 drops


4.      The ATM3/0/1.1000 of NE80E received the 10 ping packets (1 ping packets conciseness 3 Cell ) from ATM3/0/0.1000 of NE80E.

[NE80E-diagnose]display interface atm 3/0/1.1000

   30 cells input, 1590 bytes, 0 drops

   9 cells output, 477 bytes, 0 drops


5.      The ATM3/0/ 1.1000 of NE40E received the ATM PWE3 packets, and send the packets to the ATM3/0/ 0.1000 of NE40E.

[NE40E-4-diagnose]display interface atm3/0/1.1000

    9 cells input, 477 bytes, 0 drops

    30 cells output, 1590 bytes, 0 drops


6.      The ATM3/0/ 0.1000 of NE40E only received 3 correct ping packets (about 9 Cells ). The other packets were lost. We check card statistic, and find 7 CRC error.

 [NE40E-4-diagnose]display interface atm3/0/0.1000

    3 packets input, 276 bytes, 0 drops

3 packets output, 477 bytes, 0 drops


Find the card statistic, there are CRC errors.

[NE40E-4-diagnose]display atm sar sys interface atm3/0/0.1000


        OutPort Statistic:

          CRC ERR Cnt : 7 


7.      The ATM3/0/0.1000 of NE40E responds 3 ping packets. After the ATM PWE3, the ATM3 1/0 0.1000 of NE80E also find 2 CRC error. In the end, only ping packet is OK.


8.      We can make sure that when the ping packets have problem over ATM PWE3. We check the configuration and find load-balance was configured. This will results the ATM PWE3 packets into disorder. After remove the load-balance, the ATM service is OK.


Root Cause

The ATM packets from CE1 are packed into ATM PWE3 packets on NE40E. The load-balance was configured on NE40E and will result the ATM PWE3 packets into disorder. The ATM card do not have buffer in the egress direction, so the NE80E can not reorder the disorder packets. When the CE2 receive the disorder packets, the CRC check will fail, and the packets are lost.




The load-balance was configured and will result the ATM PWE3 packets into disorder. After remove the load-balance, the ATM service is OK.


The A4CF card is good at IPOA and IPOEOA, but not good at the ATM PWE3. Even so, we can still use the ping test to find the packets lost, and solve the problem.