We have several servers on our rack. All of them running Windows 2016 or Windows 2019. We always do nic teaming. For example, by combining 4 NICs we get speeds at 4Gbit (400mb/sec or so) between servers via SMB.
However, we have one Dell R420 server, running Windows 2016, which has 6 x Broadcom NetXtreme Gigabit Ethernet NIC adapters.
We have tried several configurations for that server, combining via Windows NIC teaming all 6 NICS, or 2 of them. We cannot ever get higher than 1gbit transfers out of that server.
We cannot figure out why this happens. The Link of Microsoft Network Adapter Multiplexor interface does show 6Gbit:
PS C:\Users\Administrator> Get-SmbServerNetworkInterface
Scope Name Interface Index RSS Capable RDMA Capable Speed IpAddress
10 True False 6 Gbps 10.1.1.100
10 True False 6 Gbps fe80::801a:3dc4:912f:b5c5
But speeds from/to that server are always at 1Gbit. Also multichannel looks it's working:
SMB server: >> Get-SmbServerNetworkInterface
EnableMultichannel ------------------ True
It happens only for this server. All servers are connected to the same switch.