Vyatta : Slow Network Performance x-Subnet

I’ve just moved the Vyatta device I deployed previously on Hyper-V to an ESXi environment. Initially all appeared well however yesterday I started to get some strange issues when accessing resources that were on a different subnet and thus passing through the Vyatta router.I did some simple copy paste tests and locally, in the same subnet, I was getting ~100 MB/sec, cross-subnet I was getting…wait for it… 15 KB/sec!

On further investigation the Vyatta device had ‘Flexible’ NIC’s instead of ‘vmxnet3’ NIC’s. On changing these NIC’s and reconfiguring the Vyatta device, including NAT rules, followed by a reboot I’m now getting 100MB/sec+.