Is some packet loss on a campus network natural or should a network see no packet loss at all if properly configured? I'm asking because I performed a file transfer (900 Mb) from one host to another on the same switch (3750X), same VLAN with nothing else attached to the switch. QoS was not enabled on the switchports either. When I performed a Wireshark, I noticed a few packet drops that prompted a retransmit. Is this OK? Thanks
It can be. The receiving host could be telling the sending host to slow down its transfer rate. The sending host could start backing off for a time before it starts to ramp up transfers again. Now, if you're pinging the receiving host from the sending host at the same time of sending the file, and you notice that you're losing 1 in 5 packets then you may have a problem. From your description though, retransmits are normal at times.
Aside from that, you'll also want to check your speed and duplex settings on the ports for both hosts and make sure they're both at full duplex and at the appropriate speed for your NIC
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In theory, if there's no oversubscription and there's only one flow, there shouldn't be packet loss on a network transit device that can support the transfer rate. If there's any oversubscription or more than one flow across more than one ingress port, drops are possible.
The packet drops detected by Wireshark might be caused by either the sending or receiving hosts, independent of the network switch. Do you have access to the switch's interfaces stats? Do they show any drops?
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