Yes, a slow modem can limit LAN-to-LAN links when routed through an access point or switch.
Yes, a slow modem can limit LAN-to-LAN links when routed through an access point or switch.
I possess a non-wireless modem-router (Ovislink OV604V) with several devices connected to its LAN ports. From one of those ports, an Ethernet cable stretches across your home to the router in another room. This router serves as both a wireless access point and a network switch for your PC and consoles. It handles routing and DHCP functions. You're considering replacing it with a newer model because it's outdated and struggles with 5GHz Wi-Fi, sometimes dropping connections. You're eyeing a gigabit router. You know this won't improve your internet speed directly, but since the router isn't managing routing and is merely an access point for your modem, can two devices connected to the gigabit router actually reach full gigabit speeds? For example, if your PC connects to the gigabit router and a NAS does the same, would file transfers between them perform at maximum capacity, or would they be limited by the older modem?
Examplen 2: Would linking your phone to the 5GHz network on the router enable it to download from Steam on your PC without being slowed down by the modem? The router you're considering is a D-Link DIR-867. You plan not to replace the modem soon, as your building is installing fiber and you'll wait for that before making any changes.
It will just go over the router the two are connected to, it won't go to the modem/router. Local traffic mostly goes over Layer 2 communication, which uses MAC/Physical addresses, not IP addresses. As the router (or really, the switch part of the router) knows where the devices are located by their MAC address, there's no reason to forward anything to the gateway (your modem/router).
The ideal setup is to let the device handle DHCP distribution as a modem or fiber router. Connect any switch or access point that can act as a switch to the LAN ports on this unit, and disable DHCP support on those other devices. If that isn't possible, assign different subnets—for example, 192.168.0.1 with a 255.255.255.0 mask for the modem and 192.168.1.1 with the same mask. This way, devices on separate subnets won’t communicate. My approach avoids NAT-behind-NAT setups. To restrict certain activities, group less secure devices like SmartTVs into one subnet, while keeping game consoles and PCs on the modem’s subnet. This limits exposure to malware running on the PC side. However, you’ll lose some features (like Chromecast functionality). If you’re focused on security, completely turn off DHCP and manually assign IP addresses to known devices. This is more effortful but gives better control. Assigning fixed IPs via MAC in the DHCP pool lets you forward ports as needed, while letting wireless devices join the dynamic pool.
I’m familiar with all this already. I’ve set up a single-NAT configuration for gaming, and I mentioned in my initial post that the modem handles DHCP. Both my pihole and gaming PC have static IP addresses. My concern wasn’t about configuring two separate modems and routers; it was simply whether a slower modem would slow down LAN speeds between devices connected directly to the router. The short answer is no—it doesn’t create a bottleneck. I can stream from my PC to my phone using higher speeds, because both are linked to the router, not the modem. Regarding security, my approach is avoiding smart devices altogether—they’re unreliable, and even my “Smart TV” isn’t online. I just need a basic TV since my PC is already connected directly to it.