Nortel Networks NN46110-602 - Manual (Page 110)

110 Chapter 5 Packet capture
NN46110-602
You can create new capture objects until the maximum block size reaches 25
Mbyte. (The VPN Router does not allow you to reduce the maximum block size to
less than 25 Mbyte.) If you allocate too much memory to packet capture buffers,
you receive an error message suggesting a smaller buffer size.
To check the maximum block size, select Status > Statistics and click Memory
in the Resources section. Scroll to the bottom of the window to find the maximum
block size. The output looks similar to this:
Shared Heap Statistics:
status bytes blocks ave block max block
------ --------- -------- ---------- ----------
current
free 40542960 18 2252386 39532912
alloc 64815872 135 480117 -
You can display the same information by entering the command
show status
statistics resources memory
.
Performance considerations
Running packet capture can affect VPN Router performance. You can run only
one capture object at one time for a specific source (interface or tunnel). Multiple
capture objects can exist for the same source, but only one object is allowed to
start. You can run capture objects for different sources at the same time with no
limitations.
To reduce the effect on VPN Router performance, use packet capture for
troubleshooting only and observe the following guidelines:
• Configure the capture object to capture the least amount of data needed for
troubleshooting: for example, only inbound or outbound traffic, only the first
n bytes of the packet.
• Configure a capture object for promiscuous mode only when necessary.
(Promiscuous mode affects VPN Router performance.)
• Configure filters and triggers to capture only relevant traffic, in particular if
you need to run the global IP object.