Fluctuation in windows size

Hi guys.

Windows size is fluctuating a lot.

What could be the reason?

Packet size is chopped at 1400 bytes mostly.

Can that cause lower throughput in TCP?

Hi, usually TCP window size is reduced because of different reasons, for example: physical errors on the interface, full-duplex misconfiguration, or because of too many retransmission of TCP segments. This will affect other types of traffic. Also, you may have UDP traffic claiming the bandwidth released because of TCP window reduction.

My recommendation is to force auto-negotiation on interfaces, review MTU size in all the path to avoid loses of TCP segments and look for errors or discards in network interfaces. Keep in mind that problems can be even in upper layers, but these are the most common problems.