My new DOCSIS 3.0 modem supports a Gigabit link. I use all CAT6 cables. For testing, I plugged the modem directly into my computer via the CAT6 Ethernet, and both recognized the Gigabit connection. When plugged into one of the DIR-655's LAN ports, I also get a Gigabit link. However, when plugged in to the WAN port (where I want it permanently), I only get a 100Mb link. Why is this? Is says on the DIR-655 product page that the WAN port exclusively supports Gigabit. I have tried multiple cables and manually setting the WAN port speed to Gigabit, but that setting causes the router not to properly connect with the modem (it doesn't work). This router is probably far out of warranty, as I've had it for years and years. I hope that my always reliable router (the best I've owned yet) is dying or was shipped defective (and I never knew).
Router: DIR-655 revision A4
Firmware: 1.21, 2008/10/09