1. Check that the MTU of the interface connecting the Maipu device to the NE40E
is 1500, and jumbo packets are processed as fragments.
The default MTU of the NE40E is 1500 bytes, and the value ranges from 46
current state : UP
protocol current state : UP
line protocol up time : 2018-08-27
quality grade : GOOD
Maximum Transmit Unit is 1500
Address is 126.96.36.199/30
Sending Frames' Format is PKTFMT_ETHNT_2,
Hardware address is f86e-ee98-cb79
Vendor PN is SP7041-E
The packet header obtaining result shows that the 1000-byte ping packets
sent by the Maipu device contain seven fragments. Each of the first six
fragments contain 1500 bytes, and the last fragment contains 1120 bytes. Therefore,
the MTU of the packets sent by the Maipu device is also 1500 bytes.
The payload and a 20-byte IP packet header constitute the IP packet length.
2. Obtain packet headers on the NE40E. It is
found that the packets are discarded on the NE40E.
Obtain packet headers on GigabitEthernet 2/0/1 of the NE40E
in both the inbound and outbound directions.
The Maipu device sends packets to the NE40E: seq 0~999 no packet loss
The NE40E times out in receiving some fragments and fails in
reassembly. The NE40E does not respond to the Maipu device.
The analysis shows that the problem occurs on the NE40E. GigabitEthernet 2/0/1
receives all the packets from the Maipu device in the inbound direction.
However, some fragments of the packets sent to the CPU are discarded, leading
to a CPU reassembly failure. The NE40E does not send a reply packet to the
Maipu device. This is why jumbo ping packets are discarded.
3. Check that the packet loss on the NE40E is caused by the
threshold-crossing CPU configuration.
To optimize delay processing, the NE40E is enabled with ICMP
fast reply by default when the Maipu device pings the NE40E. Specifically, data
packets are not forwarded to the CPU.
However, if the received data packets are ping packets, reassembly is required,
and the packets need to be sent to the CPU. To prevent the CPU from being attacked,
the NE40E implements CPU for such packets. The data packets with a
threshold-crossing CAR value are discarded.
It is suspected that the Maipu device sends packets at a threshold-crossing
rate, and the packets are discarded if the CAR value exceeds the threshold. The
test result shows that among the 1000 10000-byte ping packets sent by the Maipu
device to the NE40E, two packets are lost. Before the test, reset packet
<HUAWEI>reset cpu-defend car fragment statistics slot 2
<HUAWEI>display cpu-defend car fragment statistics slot 2
Application switch : Open
Default Action : Min-to-cp
Protocol switch: N/A
Passed packet(s) : 6993
Dropped packet(s) : 7
Configured CIR : 512
kbps Actual CIR in NP :
Configured CBS : 9000000 bytes
Actual CBS in NP : 9000000 bytes
Priority : af3
Min-packet-length : 128 bytes
Start time: 2018-08-27 17:22:00
End time : 2018-08-27 17:24:00
Last drop rate(pps): 0
Total dropped packet(s): 6
Time: 2018-08-27 15:05:00
Peak rate(pps): 392
When the Maipu device sends a 10000-byte ping packet,
the packet is divided into seven fragments. Therefore, a total of 7000 packets
are sent. The NE40E receives 6993 packets, and seven packets are discarded. The
NE40E discards packets at random if the CAR value exceeds the threshold. If the
discarded seven packets contain fragments of two 100000-byte packets, the two
10000-byte packets are discarded due to a reassembly failure. Consequently, two
ping packets are discarded.
4. Check that packet loss occurs due to threshold-crossing
CAR on the packets received by the NE40E.
Check the rate at which GI 2/0/1 of the NE40E receives packets.
<HUAWEI>display traffic policy statistics interface gi 2/0/1 inbound
Traffic policy inbound: 3334
Traffic policy applied at 2018-08-27 17:03:12
Statistics enabled at 2018-08-27 17:03:12
Statistics last cleared: 2018-08-27 17:08:55
Rule number: 4 IPv4, 0 IPv6
Current status: OK!
Classifier: 3334 operator or
if-match acl 3334
rule 5 permit ip source 188.8.131.52 0 destination 184.108.40.206 0
10,218,000 bytes, 7,000 packets
Last 30 seconds rate 219 pps, 2,547,688 bps
The packet receiving rate is about 2547 kbps, which is
greater than the rate specified in the cpu
car 512kbps configuration. Therefore, packet loss occurs due to threshold-crossing