Black Box TS255A Spécifications télécharger pdf (Page 56)

Not seeing traffic at the analyzer from the TAP

Chapter 5 FAQ and Troubleshooting

rev. 1

Not seeing traffic at the analyzer from the TAP

If your TAP is not transmitting to the analyzer as you expect, check

the following:

 The TAP is receiving power using a Black Box power adapter.

The Link A and Link B lights flash when there is traffic

traversing through the TAP, which indicates the TAP has

power.

 The Link is definitely up and running.

 The Ethernet/SPAN or Fiber channel are not diverted

elsewhere.

 The cable to connect to the analyzer works. Use a different

cable to confirm this.

 Try swapping the cables between the ports.

 If you are using a TAP with a GigaStor, ensure the driver

configuration speed is set correctly. Sometimes allowing it to

auto-negotiate will enable the connection. This may work for

a copper connection to the analyzer. It is not recommended

for optical connections.

 The correct SFPs are used if you are connecting to an optical

analyzer.

 Use a light meter to verify there is enough light power with

an optical TAP.

If you have checked all of the above, then a couple of common issues

may have occurred:

 If you are using an optical connection from the TAP to your

analyzer, ensure that the receive NIC on the analyzer has

auto-negotiation disabled. If auto-negotiation on the NIC is

enabled, you will not be able to see traffic from the TAP.

 If the system you are monitoring is Linux or UNIX based, you

may have an issue with the Maximum Transmission Unit size.

The TCP stack in the UNIX system uses algorithms to

produce a MTU based on response time from SYN ACK. The

TAP adds about 200 nanoseconds of delay to every packet

that comes through. Typically, this small delay is not an issue

because most responses are in the millisecond range and not

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Black Box TS255A Spécifications Page 56