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CPU Usage on NE5000Es Is High Due to PSNP Suppression by Vendor E's BAS Equipment

Publication Date:  2013-09-29 Views:  109 Downloads:  0
Issue Description

The CPU usage of two NE5000Es increased to 90%, and the CPU usage for routing processes was 45%.

The networking is as follows:

            NE5000E--------NE5000E

                     \                           /

                      \                         /

                       \                      /

                        \                   /

                          \               /

                             SE800
Handling Process

Huawei performed the following operations to diagnose the fault:

Traced and collected statistics on routing protocol packets at some interfaces and found that some interfaces sent a great number of IS-IS packets within a short period of time, as shown in the following:

10 minutes ago:

display isis statistics packet interface 

                       PDUs information for GE11/0/38.20

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

          Sent packets:

          PDU type                     Total(packets)

          L1 IIH                           0

          L1 LSP                           0

          L1 CSNP                          0

          L1 PSNP                          0

          L1 Unknown                       0

          L2 IIH                     2073650

          L2 LSP                  2392428329      ------IS-IS LSPs sent by NE5000Es

          L2 CSNP                        179

          L2 PSNP                    7640067

          L2 Unknown                       0

 

          Received packets:

          PDU type                     Total(packets)

          L1 IIH                           0

          L1 LSP                           0

          L1 CSNP                          0

          L1 PSNP                          0

          L1 IIH(error)                    8

          L1 LSP(error)                    0

          L1 CSNP(error)                   0

          L1 PSNP(error)                   0

          L1 Unknown                       0

          L2 IIH                     1812758

          L2 LSP                   512124051

          L2 CSNP                          1

          L2 PSNP                     848668              ------------IS-IS PSNPs received by NE5000E

          L2 IIH(error)                    0

          L2 LSP(error)                  421

          L2 CSNP(error)                   6

          L2 PSNP(error)                   0

          L2 Unknown                       0

 

10 minutes later

display isis statistics packet interface 

                      PDUs information for GE11/0/38.20

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

          Sent packets:

          PDU type                     Total(packets)

          L1 IIH                           0

          L1 LSP                           0

          L1 CSNP                          0

          L1 PSNP                          0

          L1 Unknown                       0

          L2 IIH                     2073724

          L2 LSP                  2392513367

          L2 CSNP                        179

          L2 PSNP                    7640434

          L2 Unknown                       0

 

          Received packets:

          PDU type                     Total(packets)

          L1 IIH                           0

          L1 LSP                           0

          L1 CSNP                          0

          L1 PSNP                          0

          L1 IIH(error)                    8

          L1 LSP(error)                    0

          L1 CSNP(error)                   0

          L1 PSNP(error)                   0

          L1 Unknown                       0

          L2 IIH                     1812823

          L2 LSP                   512154314

          L2 CSNP                          1

          L2 PSNP                     848685

          L2 IIH(error)                    0

          L2 LSP(error)                  421

          L2 CSNP(error)                   6

          L2 PSNP(error)                   0

          L2 Unknown                       0

The interface GE11/0/38.20 was used as an example. This interface sent 85038 IS-IS LSPs within 10 minutes but received only 17 PSNPs.

It was determined that the NE5000Es sent a great number of protocol packets and routing processes occupied many CPU resources. As a result, the CPU usage became high. 

Viewed the faulty interfaces, found that the interfaces were connected to SE800s, and suspected that NE5000E redelivered a lot of LSPs because the SE800s suppressed or discarded LSPs.

Contacted vendor E. Vendor E confirmed that the SE800s falsely suppressed PSNPs. Therefore, no PSNPs were sent in reply to many LSPs sent by the NE5000Es, and the NE5000Es redelivered many LSPs (at an interval of 5s by default). As a result, the CPU usage became high.
Root Cause
The SE800s from vendor E falsely suppressed PSNPs. Therefore, no PSNPs were sent in reply to many LSPs sent by the NE5000Es, and the NE5000Es redelivered many LSPs. As a result, the CPU usage became high.
Solution
Vendor E modified configurations to speed up PSNP transmission so that NE5000E could receive PSNPs in a timely manner and did not redeliver LSPs.
Suggestions
None

END