Understanding why Link B is active when Link A is offline
Chapter 8: Troubleshooting 27
redundant link if Link B goes down, and it keeps the router or switch active if the
server goes offline. Should Link A come back up, negotiations to get the link back
online are enhanced because Link B already has an active link.
As already stated, Link B is an active port. It is used to negotiate speeds for both
Link A and Link B. When you plug in Link A by itself, no negotiation occurs. If you
plug in Link B, it negotiates a link speed with whatever device is connected to
Link B. Then it negotiates with Link A at that speed. If Link A cannot use that
speed, it then negotiates with the end device on Link B at a different rate until a
compatible rate between the Link A device and Link B can be established.
One of the great advantages to having this capability is to use the nTAP to
replicate traffic to multiple devices and not use it strictly for pass through. For
example, when you use an aggregation nTAP and if you connect Link B to a SPAN,
you can then pass the SPAN traffic out the two analyzer ports and have two
copies of the SPAN traffic going to two different devices. You can have another
device receiving the SPAN data on Link A, and if you disconnect Link A, the SPAN
traffic for Link B still goes to the analyzer ports for monitoring.
An nTAP is not just for only passing bidirectional communication between Link
A and Link B and copying traffic to the two analyzer ports. Take advantage of
the active Link B port to
daisy chain
multiple TAPs together to receive multiple
sets of SPAN data streams and combine the multiple SPAN sessions into a single
stream. Without the ability for Link B to stay up if Link A were to go offline, you
lose this capability.
