Can't use ps3 online at same time as xbox online.

Do you get network access on any other network devices when this is happening or is it just the Xbox 360?

Yes I have access with my computers also.

Are they using the same port to access the router? That might be your problem.

I don;‘t believe so. I have my Xbox set up using a separate port so I can port forward.

Have you tried setting up MAC filtering making it so they will always be allowed to access the router?

I’ll attempt it.

Now I’m getting a DNS error, trying to use OpenDNS.

Nothing’s wrong with the MAC filtering though.

are they using the same IP address? I’d follow each systems address and port system and make sure there’s no clashing. Even Dynamic address fetching might pose as a problem.

Their static IPs aren’t the same, and as far as I can tell there isn’t any clashing.