F5 Throughput

Looks like there is a lower MTU somewhere in the path. When I once had a similar issue (a while back now) I found around 8 packets were being dropped (with a doubling time between each) before the F5 started sending responses with the DF (Don't Fragment) flag NOT set.

In the end I reduced the VLAN MTU (which by definition reduced the MSS the F5 would send on connection establishment) to overcome the issue. I never had any issues but I've had some quite in-depth discussions around that change and the consensus seems to be that I shouldn't have as this isn't 'standards compliant'.

PMTUD Should help with this but as firewalls tend to block ICMP traffic it can be an issue. Are you able to modify the MSS on the host sending/receiving the file(s)? That's the ideal solution.

Alternatively, you can speed things up a bit by adjusting the Maximum Segment Retransmissions value in the TCP profile assigned to the VS.

Also, the the same TCP profile, you could bump the Initial Receive Window Size to a value around 10 if the network between the F5 and end host is reliable. (Especially if the end host runs with a Linux kernal v2.6.38 or higher.