How to prevent capture on one port from capturing post transactions done by another port on the s (4278151)

port 2103 replicate demo table from server A to server B
port 2102 replicate the same demo table from server B to server A

How to prevent capture on port 2102 on server B from capturing transactions posted by poster on port 2103 on server B?

When you use the same shareplex user for port 2102 and port 2103,  Post transaction for port 2103 done on B is not captured by port 2102 capture on B.

If want the post from 2103 to be captured by capture on 2102, you can use different shareplex user for port 2102 and port 2103 in this case. 

If you have replication set up from A to B for port 2102 and port 2103 in the same direction, then you can not use the shareplex user for both ports.