Archer C7 WAN capped at 100Mbps but logs show 1000Mbps

My Archer C7 v4 had a 1000Mbps WAN connection before I installed OpenWRT and I was able to get full 200Mbps of my internet connection.

After installing OpenWRT, when I go to "Switch" in LuCi, I see the WAN port showing "100baseT full-duplex" (while local devices connected to the switch show 1000baseT Full-Duplex), allowing me to get about 90Mbps of my 200Mbps internet connection and I can't for the life of me figure out why.

I've checked system logs and I can see the following entry: kernel: [204220.811294] eth0: link up (1000Mbps/Full duplex)

Which makes me even more confused. I am almost certain the issue isn't with the cable because I had 1000Mbps/Full duplex with the original firmware and I even disconnected the cable from the WAN port and plugged it directly into my computer which also immediately picked it up and gave me 1000Mbps/Full-Duplex with 2000Mbps download speeds.

It's been almost 10 days and I still can't figure out the reason why this is happening.
I'd be forever grateful for some help.

What is the output of the following commands?

dev=$(ifstatus wan | grep \"device | awk '{print $2}' | sed 's/"//g;s/,//g'); echo "Interface: $dev, Speed: $(cat /sys/class/net/$dev/speed)"

This is the output:
Interface: eth0.2, Speed: 1000

Well, it shows 1000mbps. Try enabling software flow offloading.


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I switched that on and reconnected the cable (for the 200th time) and it switched to 1000Mbps!
BUT, got super confusing after some time:

  1. I turned off software offloading and it still remained at 1000Mbps
  2. Then I disconnected and reconnected the cable and it was still 1000Mbps (?)
  3. After like 15 disconnects and reconnects and some playing around, sometimes it would pop up as 100Mbps and sometimes as 1000Mbps
  4. I figured the pins on the cable are either dirty or not coming in contact with the router side WAN port properly, so I added an extension LAN cable to the existing (bad) one and put the original (bad) LAN cable under pressure to the ethernet coupler the using electrical tape and it started going to 1000Mbps more often.
  5. After half an hour or so, I checked again and it returned back to 100Mbps.

My conclusion: I'm pretty sure the cable is bad and it's picking interference somewhere causing the switch to fall back to 100Mbps. I will do further testing and report back in this thread, but it's not easy at all for me to replace the cable soon because it's pretty long (~30m) and goes through walls.

Thank you so much for your help and for causing me to triple check everything.

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Does your Lan cable deliver poE? Mine had 100 because of a poe switch connected to it. used another non poe switch and got GBe.

It doesn’t :confused: but thanks for the suggestion

If you can make it consistently break and restore by moving the RJ45 plug in the router socket, you may just need to put a new plug on that end of the cable.

I thought so too, but it turns out a part of the cable (out of my control/premises) shielding was broken and basically was stepped on numerous times. Replaced the whole cable and I'm consistently getting 1000Mbit now.

Conclusion: I'm an idiot - IT'S ALWAYS THE CABLE

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