First, like the others have mentioned you have no bridging loop here due to running a Portchannel. That said, running STP is still fine. Let me clear some confusions on how these commands work on Cisco switches.
spanning-tree portfast trunk
This command is supposed to be run on trunk ports towards non bridging devices, such as a server with multiple VLANs or a router. This command should not be run on trunks towards switches because the port will bypass the listening and learning phase which could potentially create a bridging loop.
If you have an interface configured like this:
interface x/x
spanning-tree portfast
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
BPDU guard will never kick in because BPDU filter is filtering both the outgoing and incoming BPDUs. This also means that the port can never lose its Portfast status which it would normally do if BPDUs were received inbound. If you remove the filter then BPDU guard will kick in and shutdown the port if a BPDU is received. This is done before the port can lose its Portfast operatational state so basically the port will always operate in Porfast operational mode.
If you apply the commands globally instead:
spanning-tree portfast default
spanning-tree portfast bpdufilter default
spanning-tree portfast bpduguard default
The first command enables Portfast on all access ports.
When BPDU filter is applied globally, the difference is that it sends out 11 BPDUs before going silent. Because normally one BPDU is sent out every 2 seconds and the default MaxAge is 20 seconds that means that if there is a device at the other end that can process BPDUs, at least one BPDU would be received when the old BPDU (if there was one) has expired.
If a BPDU is received inbound when BPDU filter is applied globally then the port stops filtering and it will lose its Portfast status.
The BPDU guard default command will only apply to ports that are in a Portfast operational state.
If you combine these three commands together then what will happen is that when a BPDU is received the port loses its BPDU filter, BPDU guard can then kick in. The port will never lose its Portfast operational state because the port is shutdown before.
So you see when applied to the interface BPDU guard can never kick in but if you apply it globally it can.
If you run just Portfast globally and BPDU filter globally then if a BPDU comes in, the port loses the filter and loses the Portfast operational state and will operate as a normal port.
Judging by your switch, I'd say you don't have the budget for a real ethernet tester like those from Fluke Networks.
Your switch is Layer 2 (L2) only and doesn't support routing, so you'd need an external router (L3) to move packets between the VLANs. I would conjecture that your random network issues were caused by either bad cabling or mismatch on speed/duplex between the switch and your systems.
You can look at using iperf configured on a server, and then have each of your client computers run a test from their respective ports to the server (one at a time), then look for interface error counters being incremented to help isolate any issues or misconfiguration.
Best Answer
WIC (WAN Interface Card) slots are small slots that accept interfaces that are primarily used for WAN connections, e.g. T1. As I recall, there were some ethernet WICs that could be used in the 37xx routers, but the actual throughput is limited in the WIC slots compared to the NM slots.
NM (Network Module) slots are larger than WIC slots, and have a higher throughput. The NM cards generally have more processing power than WICs, and can offer more LAN-type interfaces.
The 37xx series of routers went EoL (End of Life) six years ago, so Cisco no longer supports them. You will need to use a newer, larger router if the 3725 doesn't meet your needs. That is why Cisco has different models; you can choose the model that best fits your needs.
You could always use logical subinterfaces on a physical routed interface to get more interfaces for experimenting in GNS3.