It's as if the FortiSwitch is acting as a HUB rather than a switch. Now here is the strange thing, if I start a wireshark capture and have someone on the same VLAN as me start a file copy to the file server (different VLAN), my Wireshark picks up hundreds of packets all TCP Dup ACK, TCP Retransmission, TCP Spurious Retransmission between the other computer and the file server. Occasionally I will see TCP Spurious Retransmission, TCP ACKed unseen segment, TCP Out-Of-Order, TCP Dup ACK (even when I'm not really actively doing anything on the network). I noticed a couple things when I started a wireshark capture:
So then we try it again a minute later, and the performance is horrible. The second file copy we tried, it would copy around 100 MB/s all the way across (2 GB file copy). When copying files it would burst up to 108 MB/s, then drop down to 10 MB/s or below (sometimes pause for a couple seconds), then increase up to 50 - 80 MB/s, and would form this wave. It is very sporadic, which is hard to pinpoint the issue, as network performance works great and the next minute it fluctuates.įirst we started seeing that a file copy to our file server (1 GB connection) was occasionally fluctuating fast and slow. Look at adding a second card on your server.Having a new Fortinet network, we are seeing some very strange issues on the network.Look at driver updates on hardware (remember, if you update drivers, your network card advanced properties will reset).Disable everything on the server network card with the exception of flow control – under the Advanced tab.This may indicate wireless or cabling issues.Look for ethernet errors, discards, possible high utilization.Look at the path between devices and your server.If these are common, they may start to impact application and/or performance across your network.
TCP will show some packet loss, so these are normal events. These packets may indicate that the sender sent a retransmission for data that was already acknowledged. You’ll see the Wireshark main screen change to the point in time you are clicking.Īnalyze the content and look for Spurious Retransmission. Click on Statistics, IO Graphs and click throughout the graph on the color that indicates TCP errors. How do you see them? Capture some data with Wireshark on your workstation or server. TCP Spurious Retransmissions may be seen from time to time when using Wireshark.
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