Zero Windows errors are seen in captures between the VNA server end environment

Products

• Virtual Network Assurance

Issue/Introduction

Seeing a large number of zero windows errors between the VNA server the end environment. Receiving performance issue complaints from customers when in the end environment's web interface.

Environment

Component : Virtual Network Assurance For CA Performance Management

Cause

[TCP ZeroWindow] will be transmitted when the data receiver side informs the sender that "Since I cannot process any more packets, hold off sending more".  Specifically, it is displayed when a packet with TCP "Window field" set to 0 is observed along with Ack with the other party.

On the other hand, the transmission of [TCP Window Update] tells the sender that "I can continue processing, please resume transmission".  Specifically, it is displayed when packets with the same ACK number as ZeroWindow and the numerical value of its own receive buffer is set in TCP "Window field".

Finally, [TCP Window Full], this is the situation when the sending side acknowledges that the tcp window specified by the receiver is now completely full.

The most likely cause of these messages happening frequently is that the processing on the receiving side (VNA) is slow compared to the transmission speed.  

 

 

Resolution

Investegate the system specifications for the receiving system and raise them if necessary.  Memory, CPU, and even Disk I/O may be insufficient.