Ports 1 and 2 on the WS-X4418 are dedicated uplink ports and each have a dedicated 1Gbps - full duplex to the backplane. The other 16 oversubscribed ports are grouped in sets of four ports each. Each set of four ports shares 1Gbps - full duplex to the backplane.
My guess is that you can't group the dedicated ports with the oversubscribed ports.
From Cisco Docs:
The oversubscribed Gigabit ports are designed for end-station connections. Cisco does not recommend connecting these ports to switches or routers.
Each group of four oversubscribed ports has a buffer for incoming frames to allow connected devices to transmit traffic simultaneously. Because the inbound buffer is small, the default (and recommended) flow-control configuration for the oversubscribed ports is receive desired and transmit on.
You can bundle multiple oversubscribed ports into a Gigabit EtherChannel link to connect to channel-capable servers. By bundling multiple oversubscribed ports in the same port group, you might increase the total available bandwidth as compared to using a single link. However, it does provide redundancy with quick failover for links to servers and hosts that support the Port Aggregation Protocol (PAgP).
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...