Black Box TS255A Specifikace stáhnout pdf (Strana 12)

Choosing between a SPAN, Aggregator, or full-duplex TAP

Chapter 1 TAPs Overview

rev. 1

channel. For more details, see “When to use a SPAN/mirror

port” on page 12.

 Attaching a monitoring or analysis device to an Aggregator

TAP inserted into a full-duplex link.

As with a SPAN, the Aggregator TAP copies both sides of a

full-duplex link to the analyzer’s single receive channel. It uses

buffering which makes it somewhat better able to keep up

with higher traffic levels than a SPAN. For more details, see

“When to use an Aggregator TAP” on page 15 and “Choosing

an Aggregator TAP buffer size” on page 43.

 Attaching a dual-receive monitoring or analysis device to a

full-duplex TAP inserted into a full-duplex link.

Dual-receive means that the network card on the analysis

device has two receive channels rather than the transmit and

receive channels associated with a standard full-duplex link.

For more details, see “When to use a full-duplex TAP” on

page 17.

When to use a SPAN/mirror port

The advantage to using a SPAN/mirror port is its cost, as a SPAN/

mirror port is included for free with virtually every managed switch. A

SPAN/mirror port is also remotely configurable, allowing you to

change which ports are mirrored from the switch management

console.

Limitations of a SPAN/mirror port stem from the aggregation

necessary to merge full-duplex network traffic into a single receive

channel. For examples, when traffic levels on the network exceed the

output capability of the SPAN/mirror port, the switch is forced to

drop packets. Another reason that a SPAN/mirror port may not be the

right choice is because Layer 1 and 2 errors are not mirrored and

therefore never reach the analyzer. When performing network

troubleshooting, seeing these errors can be important.

When monitoring with a SPAN/mirror port on a switch, the switch

does three things:

 Copies both the send and receive data channels

 Reconstructs an integrated data stream from the two channels

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Black Box TS255A Specifikace Strana 12