Monitoring with a CA Virtual Systems Monitor › Add a CA Virtual Systems Monitor › Configure the Virtual Switch › How to Configure the Cisco Nexus 1000V › Eliminate Duplicate Packets on VLANs

Eliminate Duplicate Packets on VLANs

When the CA Virtual Systems Monitor receive two copies of a packet, for example, when you SPAN a VLAN to a CA Virtual Systems Monitor, the Packet Loss Percentage report on the Engineering page incorrectly reports an extremely high percentage of lost packets.

This section discusses how to enable the CA Virtual Systems Monitor to de-duplicate TCP packets.

Follow these steps:

1. Locate the RetransPacketDefs.ini.sav file in the C:\CA\bin directory.
2. Remove the .sav extension from the file name.
3. Edit the RetransPacketDefs.ini file. By default, the file contains the following entries:

   <no logging>
   50 1000
   10 20 30 40 50 60
   

   The first line tells the CA Virtual Systems Monitor where to log information about duplicate packets. If you replace the phrase <no logging> with a path to a logging file, such as C:\CA\bin\duppkts.txt, the CA Virtual Systems Monitor logs the information. Enabling the log file is a good practice and helps you determine whether the buffer size is adequate.

   On the second line, the first number, 50, specifies that the CA Virtual Systems Monitor maintains a buffer of 50 packets to look for duplicates. If you reduce this parameter, the CA Virtual Systems Monitor consumes fewer CPU cycles looking for duplicates. This improves CA Virtual Systems Monitor performance, but possibly finds fewer duplicates. Note that the second number, 1000, is not used.

   The last line in the file describes the bins of the histogram of duplicates, which appears in the log file specified on the first line. The histogram indicates how far each duplicate was found from its original. This information helps you tune the buffer size parameter. Ideally, lost duplicates occur in the first few bins and that the bin counts decline or disappear for the remote bins. If the counts for the high-numbered bins remain high, the buffer size is probably too small.

4. To apply your changes, restart the CA ADA Monitor service, wait 10 minutes for the management console to report de-duplicated data, and then check the Packet Loss Percentage report to verify that the packet loss percentage has decreased.

   If necessary, increase the buffer size to enable the CA Virtual Systems Monitor to search for duplicates across a larger number of packets.