more than one cable between the router and switch

I have a small home office network.
I have one Ethernet cable running from my cable modem to my router, then one Ethernet cable from the router to my 16 port unmanaged switch.
I tried running a second cable from the router to the switch and everything went straight to hell.
I thought the speed would increase or be more stable, but it went way down to like 1/10th of what it should be. I unplugged the second cable so I only have one again and my speeds are back up to where they belong.
What am I missing?
I thought that was a good thing to do.
TAI...

4 LAN ports

FINE!
back to one cable and back up to speed.
too much time on my hands this morning haha

I should have started a new thread for this but I decided to hijack my old thread
I don't know why. I'm traveling right now so I'm not in my right mind. lol
I want to create a second network at home. I have a lot of IOT devices and I want to create a network just for them. Wifi cameras and a lot of Sonoff devices. They are all on the 2.4 network.
Can I get a 5 port mega switch and plug that into my cable modem, then plug multiple routers into that?
It's the cable modem that gets the IP address from my ISP, not my router, right?
I feel like dweeb for even asking that but I found out that I don't really know the answer to this question so here I am!
TIA as usual!
.

sdtag said:

I should have started a new thread for this but I decided to hijack my old thread
I don't know why. I'm traveling right now so I'm not in my right mind. lol
I want to create a second network at home. I have a lot of IOT devices and I want to create a network just for them. Wifi cameras and a lot of Sonoff devices. They are all on the 2.4 network.
Can I get a 5 port mega switch and plug that into my cable modem, then plug multiple routers into that?
It's the cable modem that gets the IP address from my ISP, not my router, right?
I feel like dweeb for even asking that but I found out that I don't really know the answer to this question so here I am!
TIA as usual!
.

Probably not. Each router must have its own WAN IP address. Unless your cable modem is also a router, it will only supply one IP address on its LAN side. If your cable modem is also a router, then you can do what you suggest. If you cable modem is a modem only, then you will need to attach a master router to it (I would recommend an Ethernet only router with no WiFi). Then you can connect multiple sub-routers to your main router. Also, a good router will enable you to create VLAN's (Virtual LANs). This would allow you to have multiple networks spawning from a single router.

What is a VLAN (Virtual LAN)?