Black Box TS255A Spécifications télécharger pdf (Page 10)

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

Chapter 1 TAPs Overview

rev. 1

Choosing between a SPAN, Aggregator, or full-duplex

TAP

There are numerous ways to access full-duplex traffic on a network

for analysis: SPAN/mirror ports, Aggregator TAPs, or full-duplex TAPs

are the three most common. Which you use depends on the saturation

level of the link (up to 200% of link speed when both sides are

combined) you want to monitor and the level of visibility you require.

Each approach has advantages and disadvantages. SPANs and

Aggregator TAPs are designed to work with a standard (and usually

less expensive) network card on the analysis device, but their

limitations make them less than ideal for situations where it is

necessary to guarantee the visibility of every packet on the wire.

A full-duplex TAP is the ideal solution for monitoring full-duplex

networks utilized at more than 50 percent (100% when both sides are

Table 1 Pros and Cons of TAPs and SPANs

TAP SPAN/mirror port

Pros Eliminates the risk of dropped packets Low cost

Monitoring device receives all packets,

including physical errors

Remotely configurable from any system

connected to the switch

Provides full visibility into full-duplex networks Able to copy intra-switch traffic

Cons Analysis device may need dual-receive capture

interface if you are using a full-duplex TAP

(does not apply to Aggregator TAPs)

Cannot handle heavily utilized full-duplex links

without dropping packets

Additional cost with purchase of TAP hardware Filters out physical layer errors, hampering

some types of analysis

Cannot monitor intra-switch traffic Burden placed on a switch’s CPU to copy all

data passing through ports

Switch puts lower priority on SPAN port data

than regular port-to-port data

Can change the timing of frame interaction

altering response times

Bottom

line

A TAP is ideal when analysis requires seeing all

the traffic, including physical-layer errors. A

TAP is required if network utilization is

moderate to heavy. An Aggregator TAP can be

used as an effective compromise between a

TAP and SPAN port, delivering some of the

advantages of a TAP and none of the

disadvantages of a SPAN port.

A SPAN port performs well on low-utilized

networks or when analysis is not affected by

dropped packets.

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Black Box TS255A Spécifications Page 10

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