Prewarning for ARP Entry Aging Failures on MxU

Keywords: MA5616, Access network product line

Summary

The MxU products use the IPOS protocol stack. After the MxU devices run for a long time

(for example, longer than 497 days), the Address Resolution Protocol (ARP) entry learned

by some MxU devices from the upper-layer device, such as a gateway, cannot automatically

age. In this case, if the upper-layer device is replaced or cut over, and the upper-layer device

does not actively send ARP request packets to the MxU devices, the ARP entry corresponding

to the IP address of the upper-layer device cannot automatically update within a MAC address

aging period. The ARP entry recorded on the MxU devices is the MAC address of the upper-layer

device before the replacement or cutover. As a result, the MxU cannot communicate with the

upper-layer device and accordingly, the management and voice services fail.

Problem Description

Trigger Conditions

This issue occurs if the following conditions are met:

1. The MxU model and version are within the prewarning scope.

2. The system running time is longer than 497 days.

3. The device learns or updates the ARP entry of the upper-layer device when the device has

been running for 496 days.

4. The MAC address of the upper-layer device is changed.

5. The upper-layer device does not actively send ARP request packets to the MxU device to

notify the MxU device of ARP entry updating.

Symptom

The device management or voice service fails.

After the upper-layer device is replaced or cut over, the MAC address of the upper-layer device

in the ARP entry recorded on the MxU is still the original one. In addition, the ARP entry

cannot automatically update within a MAC address aging period.

Identification Method

Perform the following operations to check whether a fault complies with the prewarning:

1. Check whether the MAC address corresponding to the gateway IP address in the ARP

entry on the MxU is the actual MAC address of the gateway. The gateway IP address is

assumed to be 10.144.82.1.

MxU(config)#display arp all

{ <cr>||<K> }:

Command:

display arp all

IP Address      MAC Address    VLAN ID Port    ONT Type

10.144.82.1     00e0-fc64-756d 200     0/0 /0  –   Dynamic

10.144.82.91    001b-2191-b586 200     0/0 /0  –   Dynamic

10.144.83.224   4c1f-cc7d-6393 200     0/0 /0  –   Dynamic

—   3 entries found   —

If the MAC address recorded in the ARP entry is different from the actual MAC address

of the gateway, this fault complies with the prewarning.

2. Check whether the MxU model and version are within the prewarning scope.

3. Check whether the MxU has been running for over 497 days and whether time

reversal occurs on the MxU.

Perform the following operations to determine time reversal:

a) Check and record the system running time (Uptime).

MxU(config)#display version

{ <cr>|backplane<K>|frameid/slotid<S><Length 1-15> }:

Command:

display version

VERSION : MA5616V800R308C02

PRODUCT : MA5616

PATCH:SPC200 SPH518 HP2118

Copyright (c) Huawei Technologies Co., Ltd. 1998-2011 All rights reserved

Uptime is 2 day(s), 5 hour(s), 42 minute(s), 2 second(s)

 

b) Check and record the current system time T1.

MxU(config)#display time

{ <cr>|date-format<K>|dst<K>|time-stamp<K> }:

 

Command:

display time

2014-01-22 02:22:56+08:00

 

c) Check and record the system start time T2.

MA5616(config)#diagnose

 

MA5616(diagnose)%%su

Challenge:ZCZUBOWB

Please input password:

 

MA5616(su)%%display lastwords all

 

+++++++++++++++ Display current lastwords Info: +++++++++++++

 

**********************************************************************

System Start Time            : 2013-01-14 02:07:13.250 , Week: Fri

System Start CpuTick         : 0x00000000 908c5ce3

System Last CpuTick          : 0x000029f3 c89fd402

System Total Running CpuTick : 0x000029f3 3813771f

MilliSecs Per CpuTick        : 0x00010441

System Total Running Time    : 692301.607 (s.ms)

In normal cases, (T1 – T2) = Uptime value. The system time resets and starts timing

again after the device has been running for 497 days. If (T1 – T2) > Uptime value,

time reversal occurs.

If the fault complies with the preceding three conditions, the fault is within the

prewarning scope.

Root Cause

The ARP entry updating failure is caused by a bug of the device software in obtaining

system running time. The system time reverses after the device has been running for

497 days. If the device learns or updates an ARP entry before the time reversal, the

ARP entry becomes abnormal and fails to automatically update within a MAC address

aging period. If the upper-layer device does not actively send an ARP request message

for the ARP entry, the ARP entry does not update.

The following section provides an example to describe the fault cause: The system

running time is assumed to be Tsystem and ARP aging period is AagTime.

l When the device has been running for 497 days (Tsystem = 497), the device learns or

updates an ARP entry. Then, the ARP entry learning time is T1 = Tsystem = 497 and

the next aging time of the ARP entry is Tage = T1 + (AagTime/2) = 497 + (AagTime/2).

l In normal cases, if the system running time Tsystem reaches or exceeds Tage, the ARP

entry ages.

l However, the system time Tsystem reverses if the system running time is longer than

497 days. Therefore, after the device continues running for T’ days, the system running

time Tsystem is T’ (0 + T’). When the next ARP entry aging period starts, the system

running time Tsystem is much less than the ARP entry aging time

Tage [Tage = 497 + (AagTime/2)]. As a result, the ARP entry cannot update or age.

Impact and Risk

The management and voice services on the MxU are affected. The broadband service is

not affected.

Measures and Solutions

Recovery Measures

Run the #reset arp dynamic command on the affected MxU to rectify the fault.

MxU(config)#reset arp dynamic

This operation may take several minutes, please wait…success

Workarounds

The workarounds are the same as recovery measures.

Preventive Measures

l For the MA5612 (H832CCFE), MA5616, MA5621/MA5621A, MA5623A, and

MA5662, upgrade the device to V800R312C00 SPH208.

l For the MA5620/MA5626 (H822EPUB), Huawei will release V800R312C00 SPH209

on February 28, 2014 to resolve this issue.

l For other MxU devices, Huawei will release patches to resolve this issue. For details,

contact the prewarning contact persons.

Prewarning Retraction Conditions

This prewarning can be retracted if issue triggering conditions are not met.

Attachment

None

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