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Knowledge Base

When upgrade the ACU2 from V200R005C10SPC300 to V200R006C10SPC200, some AP will be failed to upgrade.

Publication Date:  2016-11-01  |   Views:  528  |   Downloads:  0  |   Author:  z00288884  |   Document ID:  EKB1000347590


Issue Description

All the network topology as below, The ACU2 install at DC, there are a lot of site which install AP all around county. The forward mode is directly. The capwap tunnel built at Carrier MPLS network.


When upgrade ACU2 version from V200R005C10SPC300 to V200R006C10SPC200 and AP5030DN version from V200R005C10SPC900 to V200R006C10SPC900, the AP on the site1 will online normally, but the AP on the site2 always at cfg, fault, cmt, and cmtfa states on the ACU2.

Handling Process

1: Click the upgrade file and upgrade software. All the software is complete. On the other hand, almost AP can online with R6 version, just some AP failed, so the software is well.

2: Check the network, make the normal ping test from AP which is wrong to ACU2, ping test is OK.

3: Analysis the logs, For some sites which can’t upgrade successfully, it caused by that the AP couldn’t receive the configuration package from the network, We can see the failure to deliver configurations is caused by timeout in the log.

4: Make the rollback, let the ACU2 to return the version to V200R005C10SPC300, and all the AP register at ACU2 with V200R005C10SPC900 version. The result is all AP online successfully.

5: Upgrade the ACU2 again, and capture the packets at the access switch which connect the wrong AP, at the same time, we capture the packets at s12700 connect the ACU2.

6: Analysis for package from the ACU2 side: as we can see there is a package with the size around 9500Bytes and got almost 7 fragments from the package need to transfer to the AP while the AP online.

7: But the package from the AP side we just receive 3 or 4 fragments from the network even we have tried 3 times(As we know we couldn’t lost even one fragment for the package transmission, otherwise we must retry it). So we got the config-failed or commit-failed.

8: Make the rollback, let the ACU2 to return the version to V200R005C10SPC300, and all the AP register at ACU2 with V200R005C10SPC900 version. The result is all AP online successfully.

9: we capture the packets at AP side and ACU2 side, and compare the different between R5 and R6 version. then we find that there aren’t so much size packets at V200R005C10SPC300 version.

10: At last we have made the ping test between AP and ACU2 with big size packes.

Size : 4800Bytes

Size: 9600Bytes

It shows that the network will lost the packets when the packets size is too big.

11: Check the carrier network MTU, the customers clarify that the MPLS network just support the 1500 MTU when fragment. But for HUAWEI ACU2, the default MTU is 1500, when send out the packet it will add some head byte, so it will exceed the 1500.

12: change the MTU at ACU2

<AC6605> system-view

[AC6605] wlan

[AC6605-wlan-view] ap-system-profile name ap-system1

[AC6605-wlan-ap-system-prof-ap-system1] mtu 1470

13: upgrade all the ACU2 and AP, all the AP online successfully.

Root Cause

1: The default MTU of HUAWEI device is different with others vendor.

2: There are some different between V2R5 version and V2R6 version for ACU2, because the entirely different configuration model, so  V2R6 will appear some big packets when send configuration.


Change the MTU, in order to make the network stably between HUAWEI device and other vendors.


1: Because the different from the V2R5 version and V2R6 version for AC, we must familiar with all different feature.

2: If all the network include some vendors devices, we must set the MTU, make sure that big packets will not lost.