How to Better Access and Monitor Converged Network Traffic - SPAN Ports and TAPs (
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SPAN ports and TAPs
In the past, network operators have addressed the challenge of how
to access network core traffic for monitoring purposes through the use
of switch port analyzer (SPAN) ports and/or optical TAPs. Both of these
data access methods have their advantages and disadvantages, but the
underlying common issue for both approaches is that there remains too
little access to satisfy the needs of the growing number of monitoring
tools.
Figure 1 shows a typical data access configuration employing a mix
of SPAN ports and optical TAPs. In this scenario, several different
flavors of monitoring equipment are receiving data from either the
router or a TAP. Each tool receives most, if not all, of the traffic
from the converged pipe, requiring it to process a massive amount of
data in order to get to the data it is trying to monitor.
Figure 1: Configuration employing a mix of SPAN ports and optical TAPs
SPAN ports provide a fairly straightforward approach to providing
access and can even offer some level of aggregation, assuming the
router platform is lightly utilized. The problem with this method of
data access is that the primary function of a router is not to provide
monitoring access, so burning SPAN ports on these platforms for this
purpose can quickly become cost-prohibitive. Moreover, higher level
processing functions are contingent upon the amount of resources not
being utilized for other router tasks.
Optical TAPs eliminate the cost issues related to SPAN ports but
have their own restrictions. TAPs are dedicated to a particular
test or monitoring device which, by definition, eliminates the
possibility of sharing or switching data between multiple tools.
Although they provide access at a better price point, they do so while
draining optical power. This, in turn, limits the distance between
network devices. Further, without their own processing resources, TAPs
do not alleviate the monitoring equipment's burden of too much data.
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