Nortel Networks NN46110-602 - Manual (Page 109)

Chapter 5 Packet capture 109
Nortel VPN Router Troubleshooting
• A start trigger causes the system to wait for a specific packet before it starts
saving packets to the capture buffer.
• A stop trigger causes the system to stop saving traffic in the capture buffer
after a specific packet matching the stop trigger is encountered. The packet
capture object, however, is not fully stopped. Start trigger can still restart the
capture.
A trigger works only for the direction for which the capture is configured. For
example, if you enable packet capture for outgoing traffic only, and the type of
packet that triggers the capture to start or stop arrives only in incoming packets,
the trigger does not work.
You can use triggers with filters. Like filters, triggers never match non-IP frames.
The packets that triggered the capture object to start or stop are also captured if
they match capture filters.
You can use a start trigger with a stop trigger to capture specific transaction-
oriented traffic. If you set both a start and a stop trigger, the start trigger can
reenable saving traffic to a capture buffer. You can activate both a start trigger and
a stop trigger on the same packet. In this case, only one packet is captured.
Saving captured data
By default, packet capture stops copying data to the capture buffer when the buffer
becomes full. To configure a capture object to overwrite the data in the buffer with
new data, run the
wrapping
command.
Use the command
capture save
to save captured network traffic from the
capture buffer in memory to a file on the VPN Router disk. You must stop packet
capture before you can save the buffer to a file. (See
“Starting, stopping, and
saving capture objects” on page 119 .)
Memory considerations
The number of packet capture objects that are allocated on a VPN Router depends
on the available contiguous memory. When you create a capture object, you can
specify the capture buffer size (the default buffer size is 1 Mbyte).