Ethernet connectivity issues

[dsa]

For the past three months, I've had my Macbook connected to my modem via ethernet. I got a new modem about two weeks ago and had no problems connecting via ethernet cable until a few days ago. Now, when I look at the network connections list in the System Preferences, the built-in ethernet will stay on for about thirty seconds and then go red, go green, then red repeatedly. All I know is that it's not a faulty ethernet cable. Is there any way to tell if it's a problem with my modem or with my ethernet port? I don't have any other computers to connect via ethernet. Does anyone have any ideas as to what's causing the sudden issues?

 

[spinnerlys]

Try switching off IPv6 under the Advanced settings of your Ethernet connection.

Does that help?

 

[dsa]

Try switching off IPv6 under the Advanced settings of your Ethernet connection.

Does that help?

Unfortunately it's still going red/green/red/green.