Endace DAG 4.3GE, Руководство пользователя

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Endace Measurement Systems Ltd EDM01.05-01r1 DAG 4.3GE Card User Manual
www.endace.com
5.1 Starting Capture Session
, continued
Process (continued)
Process Description
Setting capture session
parameters
Parameters are set with
dagfour
.
The card can operate in two modes, variable
length capture (
varlen
), and fixed length
capture (
novarlen
).
In variable length capture mode, a maximum
capture size is set with
slen=N
bytes. This
figure should be in the range 32 to 10240 and is
rounded down to the nearest multiple of 4.
Packets longer than slen are truncated. Packets
shorter than slen will produce shorter records,
saving bandwidth and storage space. Full packet
capture for example:
tools/dagfour –d dag0 varlen
slen=1536
Capturing non-
standard ethernet
frames. For frames larger than 1500 Bytes in size,
known as Jumbo frames, the value of ‘long’ is
increased. For example, for full payload Jumbo
frame capture:
tools/dagfour –d dag0 varlen
slen=9600 long=9600
Setting fixed length
mode. In fixed length mode, packets longer than the
selected slen are truncated to slen.
Packets shorter than slen produce records
padded out to slen length.
Large slen values in fixed length mode should
be used because short packets arriving produce
large padded records, wasting bandwidth and
storage space.
An example, for fixed length 64-byte records,
choose slen=44 (64 – ERF header size of 16 –
alignment padding 4) is:
tools/dagfour –d dag0 novarlen
slen=44
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Revision 6. 22 September 2005.