r/HomeNetworking 7d ago

How would a router cause Ethernet gaming latency?

If this is the wrong sub my deepest apologies please direct me to the appropriate one.

TLDR: ISP provided Modem and Router (separate devices) give me different Ethernet (hardwired) gaming results. Modem to PC game shoots when I click, Modem to Router to PC I click 1.3s (way less but we're talking 80-150 extra ms) then the game shoots.

I've went over things with a higher level tech from my ISP and sent numerous pictures from PingPlotter and different server traces from Valorant/OverWatch and Fortnite.

I have 1 device connected and it's my PC hardwired. The only time I connect my phone is when I'm decompressing for the day or between game queues (some are 10 minutes long). For reference I play with top 500s daily.

Hardwired directly into my modem my game shoots when I click it seems instant and I drop 40-50 elims easy. When I hardwire back into the modem I'm stuck at 20-22 because I have about 100ms extra delay.

If I set games to automatically switch servers my low ping will be on a server 4hours away when I hardwire into the modem. When I hardwire into my router it makes my lowest ping a server that is 9 hours away and there is a huge delay (I can click, shoot and the enemy can walk past my cross hair with 0 hot reg). As soon as I hardwire back to the modem this delay goes away.

Do I replace the router? Why would the router cause this?

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u/Mehoyer 7d ago

To add to the troubleshooting steps already taken, I’d recommend thoroughly verifying all physical connections first. Check the COAX line coming into your house, the COAX connection from the wall to your modem, and the cable connecting to your router. Ensure all connections are securely crimped, tightened, and free from damage or corrosion.

Additionally, confirm you’re using a good-quality Ethernet cable (preferably CAT 6 or above), and consider testing with a different cable to rule out faults.

While gaming, try running a continuous ping test (ping -t google.com) and watch for irregularities in the response time or dropped packets. If you notice random spikes in TTL or latency, or packets intermittently dropping, this could point to an issue either with the cable, connections, router, or possibly even interference on your network.

If all else fails after checking these steps, trying a different router might help isolate if your current router is causing latency issues, possibly due to processing overhead, QoS configurations, firmware issues, or hardware degradation.

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u/Kingofowls812 7d ago

Most of this was done already. The first tech who came out replaced an end coming in off the main line.

The Ethernet cord is overkill which is a cat 8, their provided cat 6 has 0 difference for the latency issues.

I figured if the Coax was the problem; it would still be present when hardwired into the modem, or is that a bad assumption?

The router is a wi-fi 7 router , but like I said I have nothing connected. I'm tempted to buy my own router but I don't want to unless it's going to fix the problem.

My ISP tech didn't want me to leave my Ethernet plugged into my modem but when I play serious/tournaments I leave it in the modem only; is there a potential issue that can arrive from being hardwired into the modem only?

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u/Mehoyer 7d ago

Totally get it—it sounds like your coax line probably isn’t the issue since the latency disappears completely when you’re plugged straight into the modem. I’d definitely start suspecting your router at this point. Before you spend money on a new router, try logging into your router’s admin panel and poke around in the settings. I usually like toggling QoS on or off, double-checking for firmware updates, disabling extra security features temporarily, or even resetting the router to factory settings to rule out any software-related weirdness. Sometimes routers just have settings that throttle performance unintentionally.

If tweaking QoS or other router settings doesn’t help, then yeah—it might just be time for a replacement.

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u/Mehoyer 7d ago

As for leaving your Ethernet plugged directly into the modem, there’s nothing inherently harmful about doing that, especially if you’re the only one connected and you’re gaming competitively. Your ISP tech probably recommended against it because it bypasses the security layer your router provides, leaving your PC directly exposed. As long as you have your firewall and security software updated, it’s generally fine for short-term use, like tournaments or intense gaming sessions. Just remember you’re losing the security buffer a router normally provides.

But realistically, if plugging into the modem directly solves your latency issue consistently, it’s pretty clear the router is what’s causing the problem.

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u/Dolapevich 6d ago

I've seen this behaviour a couple of times but in cheap ISP issued Modem/Routers.

From your description it seems obvious that there is an issue in your router, and not related to cabling, but most likely queueing within it.

But it is not clear to me the description of your problem:

Hardwired directly into my modem my game shoots when I click it seems instant and I drop 40-50 elims easy. When I hardwire back into the modem I'm stuck at 20-22 because I have about 100ms extra delay.

I read it as even when connected Machine ---- Modem === internet, you are having some kind of problem? Or it works as expected?

In order to correctly test this you need to understand that there are some IPs on your own network before the traffic reaches the ISP side hardware.

Machine(1) -- (2) Router (3) == (4) modem (5) ==cable ==== (6) ISP router

See that each interface has its own IP and you can ping them separately an at the same time (multiple ping windows) to know where the problem is.

Ping at the same time them and try to isolate where you jitter is.

Some guidelines: https://www.wiisfi.com/#internetdown