Net Optics iTap 10 GigaBit Port Aggregator User Manual
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iTap 10 GigaBit Port Aggregator
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CRC Sanitizing
The iTap Port Aggregator can be set to drop packets from the monitoring data stream
if they are received with CRC errors. This function can clean up the data being
sent to monitoring tools, or it can be left off so the monitoring tool can see the
packets that have CRC errors. In either case, packets received with CRC errors are
counted and reported in the Port Statistics. All packets are always passed between
Network Ports A and B regardless of CRC errors; this option only affects the traffic
sent out the Monitor Ports. CRC Sanitizing is activated by setting Drop Bad Packet
to ON.
CRC Regeneration
The iTap Port Aggregator can regenerate good CRC check bytes for packets as it
copies them to the Monitor Ports. The four bytes of regenerated CRC are appended
to the packet. For example, if packet slicing is set to 64 bytes, the resulting packet
with CRC Regeneration is 68 bytes at the Monitor Port.
Timestamping and packet slicing inherently create packets with bad CRCs, so use
CRC Regeneration if you don't want the monitoring tool to receive timestamped or
sliced packets with CRC errors.
However, note that CRC Regeneration also converts packets with CRC errors to
good packets before copying them to the monitoring tool. This situation should be
avoided because the monitoring tool won't know the packets were received with
CRC errors. Therefore, whenever CRC Regeneration is ON, it is advisable to turn
on CRC Sanitizing as well, to prevent packets received with CRC errors from go-
ing to the Monitor Ports at all.
SNMP Traps
The iTap Port Aggregator transmits SNMP traps for the following events:
• Utilization exceeds the threshold on any port
• Any port link status changes
• Either power supply state changes