This router started shipping in 2003. They can go bad. Troubleshooting costs so much that I carry a cheap router to show where the problem is and how a 20 buck router can be the answer.
As a test I pull the router back to 802.11g only connections. Sure that's only 54 megabit but that's 5 times the speed you have now.
Now here's another thing. The Linux angle tells me it's hardware IF other machines are same or fine. I happen to have a dv6 and they do tend to need new WiFi cards after a few years.
All this is inconclusive but you will get clients that can't accept a card or router has failed. Which is great news for your billing!
My laptop (HP dv6-1330ca) will only ethernet connect (sometimes I need to) at 10 Mbps while wireless is a full 104 Mbps; I'm not super sharp with networks and I've pretty much exhausted my troubleshooting abilities so hoping someone here can point me right.
- my laptop insists on ethernet connecting to my dLink DIR-655 router at 10 Mbps; (this computer is max 100 Mbps) .
- for the purposes of troubleshooting, I reset DIR-655 to factory settings.
- the cable is known good. Everything has been rebooted (several times actually).
- other devices can connect to the dLink at the appropriate speed (1000 or 100).
- likewise this computer can connect to 2 other routers (Bell, Linksys) at the proper 100 Mbps.
- this behavior is recent - it was fine before today on the dLink; couldn't find anything in Windows Events to explain it.
- eventually I upgraded the Windows driver (even though I never really thought that was the issue).
- also has the exact same behavior in Linux.
Backgound: Normally I use the DIR-655 as a switch/ alternate wireless access (mainly because the ISPs router is really bad at in-home streaming).

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