And because it's so sporadic, we'll think we have it solved, and then it starts doing the same again. Whatever is happening is completely deteriorating our network performance. It's as if the FortiSwitch is acting as a HUB rather than a switch. Spurious Retransmission (added in the latest versions of Wireshark), also referred to as fake Retransmission, are not real retransmissions. 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. of the Wireshark package, was used to gather the packet count statistics. 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. tcpanaly, which helps to prevent spurious triggers of retransmission methods. Having a new Fortinet network, we are seeing some very strange issues on the network. Why machine A is retransmitting the packet if B already sent an ACK with sequence number higher This retransmissions decrease the TCP congestion window to the half as part of the congestion avoidance algorithm, and if they happen close one after each other, the overall throughput is affected.
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