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Ping Packet Loss Occurs After an NE40E Is Upgraded Because the CPU-defend CAR Configuration Is Changed on the LPU

Publication Date:  2013-01-07 Views:  51 Downloads:  0
Issue Description

An NE40E was upgraded from V600R001C00SPCc00 to V600R001C00SPCf00 at the LTE Backhaul site in K country in November 2011. Based on the customer feedback, a non-Huawei router accessed a ring device and pinged the Huawei router MCOT after the upgrade. As a result, the packet loss occurred. Before the upgrade, no packets loss occurred in the ping process. Additionally, no packet loss occurred when the non-Huawei device was pinged before and after the upgrade. Therefore, the customer doubted that the problem lied in the new version running on the Huawei router MCOT and required that the fault be rectified as soon as possible.

Version: V600R001C00SPCf00

Handling Process

1.         The packets sent in the ping operation are 1900 bytes. Eight ping packets are sent every second. The packet loss occurs when multiple access-ring devices ping the Huawei router MCOT. The physical links vary in different scenarios. After a check of the physical interfaces, no error packets are transmitted and the CRC rate is not increased. Therefore, the problem does not lie in the physical link failure. A check of the MCOT configuration shows that no traffic rate limit is configured. However, the number of lost ICMP packets in the cpu-defend CAR statistics increasing continuously. The command output is shown as follows.

< KJKJ_X8_MCOT11>display cpu-defend application-apperceive statistics slot 2

Slot Attack-Type Total-Packets Passed-Packets Dropped-Packets

2 Application-Apperceive 837917 834765 3152

--------------------------------------------------------------------------------

FTP SERVER 0 0 0

SSH SERVER 0 0 0

SNMP 0 0 0

TELNET SERVER 25 25 0

OSPF 811666 811666 0

……………………………..

ISIS 0 0 0

ICMP 25014 21862 3152 ---grow continuously

802.1AG 0 0 0

FTP CLIENT 0 0 0

TELNET CLIENT 1212 1212 0

The display cpu-defend statistics command displays detailed information about the discarded packets to be sent to the CPU. application-apperceive specifies the rate for discarding packets through application layer association.

2.         The count of destination unreachable packets is displayed in the statistics about the ICMP packets. The command output is shown as follows.

< KJKJ_X8_MCOT11>display icmp statistics

Input: bad formats 0 bad checksum 0

echo 292101 destination unreachable 234900 ---grow continuously

source quench 0 redirects 0

echo reply 240 parameter problem 0

timestamp 0 information request 0

mask requests 0 mask replies 0

time exceeded 26

Mping request 0 Mping reply 0

Output:echo 611 destination unreachable 0

source quench 0 redirects 0

echo reply 292101 parameter problem 0

timestamp 0 information reply 0

mask requests 0 mask replies 0

time exceeded 718

Mping request 0 Mping reply 0

3.         It is doubted that the configuration of the cpu-defend car command on the NE40E causes the packet loss. Check the ICMP cpu-defend car configuration on the LPU and the command output is as follows.

< KJKJ_X8_MCOT11>disp cpu-defend car protocol icmp statistics slot 2

Slot : 2

Application switch : Open

Default Action : Min-to-cp

--------------------------------------------

ICMP packet

Protocol switch: Open

Packet information:

Passed packet(s) : 311923

Dropped packet(s) : 1086

Configuration information:

Configged CIR : 1000 kbps Actual CIR in NP : 1000 kbps

Configged CBS : 1000000 bytes Actual CBS in NP : 1000000 bytes

Priority : high

Min-packet-length : NA

Calculate the rate at which the packets are sent in the ping operation: 1900 bytes × 8 × 80 = 1216 kbytes > 1000 kbytes Therefore, the problem is caused by the cpu-defend car configuration on the LPU. The cpu-defend car is 4000 kbytes on the LPU in V600R001C00SPCc00. Therefore, no packet loss occurs before the upgrade but occurs after the upgrade.

Root Cause

The packet loss occurred because the default bandwidth at which the ICMP packets are sent to the CPU is reduced after the upgrade.

Solution

Increase the value of CP-CAR to enable the ping operation to function normally. The configuration is as follows:

cpu-defend policy 2

car icmp cir 4000

slot 2

cpu-defend-policy 2

END