Data Capture Files
rvtrace can write packets into a capture file, and read a stream of packets from a file (as if from the network).
Motivation
Packet capture files are an important tool for problem diagnosis. Several techniques are useful:
| • | Capture packet data for later analysis. |
| • | Capture packet data for further analysis at a remote location. |
| • | Capture packets at high speed, then replay later when I/O delays are acceptable. |
In general, rvtrace can capture packets to a file faster than it can display statistics. Large amounts of display data can create I/O delays, which could cause rvtrace to miss packets. For example, in a heavily loaded network, displaying subject statistics for many subjects could have this undesirable result.
You can use data capture files to side-step this difficulty. For example, capture a five-minute snapshot of packets (capturing suppresses display); then replay packets from the file, displaying statistics when the consequences of I/O delays are no longer problematic.
Output File Rotation
The rotation regimen for data capture output is almost identical to the rotation regiment for log files; see Log Rotation.
The only difference between them, is that rvtrace always deletes an older existing file before opening a file for writing packet data. (That is, it never appends to the end of an existing data capture file.)
Output Rotation Backward Compatibility
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The command line option In the meantime, we preserve backward compatibility by converting the value of this deprecated parameter to corresponding values of the new parameters:
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